Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session JP11: Poster Session IV:
Poster
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Room: Hall A |
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JP11.00001: ASTROPHYSICAL PLASMA PHENOMENA
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JP11.00002: STUDY OF THE ZEEMAN SPLIT IN HYDROGEN IN MG MAGNETIC FIELDS Vladimir V Ivanov, Roberto C Mancini, Kyle J Swanson, Noah A Huerta, Igor E Golovkin, Don E Winget, Michael H Montgomery A Zeeman effect is used for investigation of magnetic fields in astrophysical and laboratory plasmas. Magnetic fields in the atmosphere of magnetic white dwarf stars are in the range of 1 - 100 MG. A quadratic Zeeman effect may contribute to the line split in this range of magnetic fields. |
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JP11.00003: Positron-acoustic solitons in an electron-positron plasma with beam electrons and kappa-distributed electrons Ashkbiz Danehkar Electrostatic solitary waves are typically observed in space plasmas containing distinct electron populations with different temperatures. However, electron-positron pairs are also produced in dense high-energy astrophysical plasmas such pulsars and microquasars, leading to the formation of positron-acoustic solitary waves in high-energy environments, where the population of background suprathermal hot electrons does not follow a Maxwellian distribution. Moreover, the presence of magnetic fields in such a plasma leads to the injection of field-aligned beam electrons. In this work, the existence of positron-acoustic solitons is investigated in an electron-positron plasma penetrated by an electron beam, containing inertial positrons, inertial electrons, and background suprathermal hot electrons modeled by a κ-distribution function. A nonlinear pseudopotential method is employed to determine the existence of positron-acoustic solitary waves and their dependence on electron beam, positrons, and electron suprathermality. The results will improve our understanding of electrostatic solitary waves formed in high-energy astrophysical plasmas characterized by electron-positron pairs, magnetic field-aligned beam electrons, and κ-distributed electrons. |
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JP11.00004: Reinstating gauge invariance for gravitational-wave coupling to plasma Deepen Garg, Ilya Y Dodin The recent observations of gravitational-wave (GW) bursts accompanied by electromagnetic (EM) radiation has revitalized the interest in the coupling between GWs and EM fields. However, a rigorous theory of this coupling is yet to be developed. In particular, reduced models of GWs in matter are typically contaminated with gauge artifacts. To fix this, we show how to find the gauge-invariant part of the metric perturbation in an arbitrary background metric (arXiv:2105.04680). We also propose a gauge-invariant adiabatic quasilinear theory and geometrical optics of dispersive GWs in matter (arXiv:2106.05062). We also show how gauge invariance can be maintained within a given accuracy if nonlinearities are included up to an arbitrary order in the GW amplitude. |
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JP11.00005: A heating mechanism for high-β plasmas in galaxy clusters Francisco Ley, Ellen G Zweibel, Mario Riquelme, Lorenzo Sironi Turbulence driven by supermassive black hole activity, gravitational infall, and galaxy motions is an attractive energy source for heating the intracluster plasma (ICM) in galaxy clusters. However, how this energy dissipates into heat is unclear, since the ICM is collisionless1. In this work, we perform particle-in-cell (PIC) simulations of a plasma subject to a periodic variation of the mean magnetic field, B(t), to show that particles can be heated by gyroviscosity via magnetic pumping. When B(t) grows (dwindles), a pressure anisotropy P⊥>P∥ (P∥>P⊥) builds up due to the adiabatic invariance of the particle's magnetic moment. When initially β=20, the plasma self-regulates its anisotropy by exciting the Mirror (P⊥>P∥) and Firehose (P∥>P⊥) instabilities. In this process, both instabilities pitch-angle scatter particles, breaking their adiabatic invariance and providing a channel to efficiently retain some energy in the plasma after one pump cycle, therefore effectively heating the system. The efficiency at which this mechanism acts depends on the level of macroscopic turbulence and how fast the instabilities can be excited and saturate. Our results show that this process can be relevant in dissipating and distributing turbulent energy at kinetic scales in the ICM. |
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JP11.00006: On trapped particle motion in a strong magnetic field Mikhail V Medvedev Neutron stars and magnetars possess extremely strong magnetic fields, so that radiative cooling of particles in their magnetospheres can be short compared to a plasma dynamical time. The magnetospheres are observed to produce strong flares, possibly due to reconnection, which is a source of high-energy particles. How does the particle distribution change as these particles propagate in the magnetospheric `magnetic bottle'? Here we derive the equations that describe the motion of a relativistic `larmor particle' in a straight magnetic bottle subject to synchrotron energy loss. This result can be important for studies of a plasma around neutron stars and magnetars. |
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JP11.00007: Particle-In-Cell Simulations of Mildly Relativistic Outflows In Kilonova Emissions Mohira N Rassel, Patrick F Kilian, Chris Fryer, Nicole M Lloyd-Ronning, Federico Fraschetti Collisionless shocks are ubiquitous in astrophysical plasmas, and are observed to be the production sites of very high energy particles (which then radiate over a wide range of the EM spectrum). A long-standing, unsolved problem in high energy astrophysics is how magnetic fields are generated in these shocks, and how these fields relate to the particle acceleration process. Particle-in-cell codes are ideally suited to address this question. Previous work has looked at cases of magnetic field generation and particle acceleration in both highly relativistic and non-relativistic shocks. Our aim is to examine shock development, magnetic field generation and particle acceleration in the case of mildly relativistic shocks, which are expected when the tidal ejecta of neutron star mergers drive a shock into the external medium. Using LANL's VPIC (vector particle-in-cell) code we have run simulations of such mildly-relativistic, collisionless, weakly magnetized plasmas and compute the resultant magnetic fields and particle energy spectra. We show the effects of varying plasma conditions, and explore the validity of using various proton to electron mass ratios in VPIC. Our results have implications for observing late-time EM counterparts to gravitational wave detections of neutron star mergers. |
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JP11.00008: General relativistic particle-in-cell simulations of compact neutron star magnetospheres Rui P Torres, Fabio Cruz, Thomas Grismayer, Ricardo A Fonseca, Luis O Silva Magnetospheres of compact objects such as neutron stars and black holes are complex systems where quantum electrodynamic (QED) processes, kinetic-scale pair plasma physics and general relativity (GR) play all an important role. To study such intricate and exotic systems, advanced simulation techniques are required. In this work, we present a GR module recently developed for the particle-in-cell (PIC) code OSIRIS. PIC simulations treat the plasma as particles and capture the self-consistent coupling between particles and fields down to the plasma kinetic scales. All algorithms in this GR-PIC module of OSIRIS (field solver, particle pusher and current deposit) support Minkowski, Schwarzschild or the slow-rotation limit of the Kerr metric. We present two-dimensional simulations of isolated neutron star magnetospheres, where QED processes are mimicked by injecting plasma at the stellar surface. We discuss the differences in the plasma current distribution in the vicinity of the star for different ratios between the Schwarzschild and the stellar radii, identifying possible locations of unscreened electric field and potential emission of coherent radiation. Finally, we compare analytical estimates of the polar cap geometry with simulations in the force-free regime. |
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JP11.00009: Magnetic topology in coupled binaries Maxim Y Lyutikov, Sergey Cherkis We consider topological configurations of the magnetically coupled spinning stellar binaries. We discuss conditions when the stellar spins and the orbital motion `compensate' each other, leading to periodic untwisting of the magnetosphere; such untwisting can be global and/or local. We describe the topology of the relevant space as $SO(3)=\mathbb{R}P^3$ or $\mathbb{F}=STS^2$ and find conditions for `unwinding' configurations in terms of magnetic moments, spins and orbital momentum. These conditions become ambiguous near topological bifurcation points as they depend on the details of the magnetic field dynamics. |
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JP11.00010: Why astrophysical ice dust grains should be elongated Paul M Bellan Models of interstellar dust alignment assume that dust grains are elongated but none of these models explain why dust grains should be elongated. On the other hand, models of interstellar dust grain growth assume that dust grains are spherical and not elongated. We show that when dusty plasma effects and the dipole moment of water molecules are together taken into account, it is concluded that astrophysical ice grains should be prolate ellipsoids and not spheres [1]. Dusty plasma analysis shows that an ice grain is charged to a negative potential that has magnitude nearly equal to the electron temperature. Several different mechanisms causing deviation from sphericity are identified; these mechanisms involve the interaction of the dipole moment of water molecules with electric fields associated with ice grain charging. These mechanisms include focusing of water molecule trajectories, migration of water molecules in a quasi-liquid layer on the grain surface towards regions where the electric field is strongest, enhancement of this migration by bombardment of energetic protons that gain energy upon falling into the ice grain negative potential, and mutual repulsion by electric charges having the same sign. The aspect ratio is established shortly after the ice grain is formed and then is maintained as the grain grows. |
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JP11.00011: Astrophysical Evidence of Wakefield Acceleration in Galactic and Extragalactic Jets via Gamma Rays and UHECRs Greg Huxtable, Noor Eltawil, Wei-Xiang Feng, Wenhao Wang, Gabriel Player, Toshiki Tajima, Toshikazu Ebisuzaki We show data not only supports but suggests that wakefields are the driving force inside AGN jets exhibiting gamma ray bursts and localized ultra-high energy cosmic ray (UHECR) emissions. Data from a virtually comprehensive list of astrophysical objects ordered by central mass (in the range of 1 – 109 M⊙) that host jets was compared with theoretical predictions. For example, blazars temporal structure, which includes correlations in neutrino and gamma-ray bursts, and anti-correlation in flux and index, can be explained within the framework of accretion disk evolution along with a coherent collective acceleration process such as wakefield acceleration (WFA). Blazars (∼ 109 M⊙), radio galaxies (∼ 108 M⊙), Seyfert galaxies (∼ 106 M⊙), starburst galaxies (∼ 103 M⊙), down to microquasars (1 – 10 M⊙) all interestingly exhibit the same physics since the accretion and acceleration processes are independent of mass, aside from maximum values. Theory also suggests this mechanism is likely accompanied by related emissions, such as high-energy pin-pointed neutrinos, time varying radio, optical, and X-ray emissions — opening up an opportunity to characterize these astrophysical objects via multi-messenger approaches. |
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JP11.00012: Wakefield Acceleration in a Jet from a Neutrino Driven Accretion Flow around a Black Hole Yoshiaki Kato, Toshikazu Ebisuzaki, Toshiki Tajima We have investigated electromagnetic pulses in a jet from a neutrino driven accretion flow (NDAF) around a black hole. NDAFs are massive accretion disks of accretion rates M ̇ ≈ 0.01−10M⊙/s for black holes of several solar masses M ≤ 10M⊙, such extreme accretions are investigated as a model of gamma-ray bursts (GRBs) as well as supernovae and hypernovae. Recently, Ebisuzaki & Tajima 2019 (ET19) have proposed a model of acceleration mechanism of charged particles to very high energies ∼ 1020 eV by electromagnetic wave-particle interaction. If episodic eruptive accretions generate Alfv ́enic pulses along large-scale structured magnetic field in the jet, such Alfv ́enic pulses act as a driver of the collective accelerating pondermotive forces which drive the wakes whose direction is parallel to the motion of particles. Because the wakes propagate at the same speed with the particles, the so-called wakefield acceleration has a robust built-in coherence by the acceleration system itself. |
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JP11.00013: Scaling of Small-scale Dynamo Properties in the Rayleigh Taylor Instability and Stably Stratified Turbulence Valentin Skoutnev, Amitava Bhattacharjee, Elias R Most, Alexander A Philippov, Jonathan Squire Fluid instabilities in astrophysical plasmas are ubiquitous and understanding their efficacy for triggering the dynamo process is essential for understanding the origin of magnetic fields in space and astrophysical plasmas. The first part of this poster proposes simple, theoretical scalings of small-scale dynamo properties for the Rayleigh-Taylor instability and tests the predictions with direct numerical simulations. The scaling relations allow a quantitative prediction of the net magnetic amplification and time dependence of the dynamo growth rate. The second half of the poster focuses on small-scale dynamo in stably-stratified turbulence. Stratified turbulence in stellar radiative zones driven by shear instabilities or breaking internal waves should conceivably drive small-scale dynamo action due to the high conductivity of stellar plasma. This mechanism could provide a source of magnetization in more massive stars with extended radiative zones. We present investigations into three principle properties of the small-scale dynamo in stably stratified turbulence–the onset criterion, the growth rate, and the nature of the magnetic field anisotropy. Using our Sun as a representative star, we find that the stratification is strong enough to make the small-scale dynamo active in the solar tachocline for thermal Prandtl number Pr=1. |
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JP11.00014: Continuum-kinetic studies of the Rayleigh-Taylor instability John Rodman, Petr Cagas, Bhuvana Srinivasan Rayleigh-Taylor (RT) instabilities are ubiquitous in plasma physics from astrophysical to laboratory regimes but are traditionally studied using fluid models. In this work, the continuum-kinetic capabilities of the plasma simulation framework Gkeyll are used to simulate the RT instability in 2X3V (2 spatial and 3 velocity space dimensions) for neutral species and 2X2V for plasma. In the neutral case, the effect of collisions on energy transport and RT growth is studied by varying collision mean-free-path. Plasma RT simulations are performed in a kinetic regime, where finite Larmor radius effects become relevant. |
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JP11.00015: Buoyancy of Cosmic Ray Loaded Magnetic Flux Tubes in the Galactic Disk Roark S Habegger, Ellen G Zweibel Interstellar gas in disk galaxies is vertically supported against gravity by the pressure of thermal gas, magnetic fields, and cosmic rays. When nonthermal pressure support exceeds a threshold, the Parker instability can appear. Like the Rayleigh-Taylor instability, over-dense regions sink, and under-dense regions rise. This produces peaks and valleys in the magnetic field. Gravitational energy provides the free energy necessary to compress the interstellar gas into the valleys. |
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JP11.00016: On the origin of observed cosmic ray spectrum below 100 TV Igor V Moskalenko, Mikhail A Malkov Significant progress in cosmic ray (CR) studies was achieved over the past decade. Particularly important are precise measurements of primary and secondary species in the TV rigidity domain that show a bump in the spectra of CR species from 0.5--50 TV. In this presentation, we argue that it is likely caused by a stellar bow- or wind-termination shock that reaccelerates preexisting CRs, which further propagate to the Sun along the magnetic field lines. This single universal process is responsible for the observed spectra of all CR species in the rigidity range below 100 TV. A viable candidate is the Epsilon Eridani star at 3.2 pc from the Sun, which is well-aligned with the direction of the local magnetic field. We provide a simple formula that reproduces the spectra of all CR species with only two nonadjustable shock parameters, uniquely derived from the proton data. We show how our formalism predicts helium and carbon spectra and the B/C ratio. |
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JP11.00017: MFE :EXHAUST & PMI; DISRUPTIONS AND RUNAWAY ELECTRONS; ENERGETIC PARTICLES
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JP11.00018: A Molten Lithium Divertor Concept for Heat Flux Handling Beyond 10 MW/m2 Employing Advanced Cooling Geometries James Bramble, Cody Moynihan, Steven Stemmley, David Underwood, Geoff Campbell, David N Ruzic This work investigates the milli-LiMIT divertor concept, that utilizes liquid lithium flow through a patterned substrate to remove fusion-relevant heat fluxes. Previously, lithium has been shown to promote lower recycling operation in the edge plasmas leading to longer confinement times and higher power density in the plasma. UIUC previously developed the LiMIT (Lithium Metal Infused Trenches) concept which harnesses the heat and magnetic fields already present in fusion devices to drive lithium flow via thermoelectric magnetohydrodynamics (TEMHD). This concept has shown its ability to facilitate molten lithium flow while handling large heat fluxes, above has previously demonstrated their micro-cooling channels can remove from semiconductor systems. Using this advanced cooling geometry the milli-LiMIT divertor concept was developed by in conjunction with UIUC, based on the LiMIT design. Prior to testing of the milli-LiMIT part, lithium's ability to wet the small features and its corrosive nature to the fabrication method used by M is investigated. Once completed the part will be tested under a high heat flux produced via electron beam. The high heat flux tests will work to verify the computational models developed by which show milli-Limit has the capabilities to remove heat fluxes beyond . |
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JP11.00019: Potential Evidence of Helium Pumping by Lithium During HIDRA Steady-State Plasmas Andrew J Shone, Zachariah Koyn, Jean Paul Allain, Daniel Andruczyk The Hybrid Illinois Device for Research and Applications (HIDRA) at the University of Illinois Urbana-Champaign is a tokamak-stellarator hybrid dedicated to the study of plasma material interactions with an emphasis on liquid metal plasma facing component (PFC) research. HIDRA is capable of creating a steady-state plasma of which a 1000 s helium plasma has been demonstrated. The HIDRA Material Analysis Test-stand (HIDRA-MAT) enables in-vacuo liquid metal PFC characterization after exposure to HIDRA plasmas. LIBS and TDS results have shown no change in helium retention of the tungsten substrate with the introduction of liquid lithium to the surface after exposure to a 900 s helium plasma. However, some exposures resulted in the lithium completely evaporating from the sample surface, resulting in a significant change in plasma behavior. The introduction of lithium into the plasma in-situ resulted in a reduction of plasma impurities. Once the evaporated lithium was ionized, spectroscopy and pressure measurements indicated a drop in helium content in HIDRA even though there was a constant helium flow rate into the chamber. The scope of this work will cover an in-depth discussion on helium-lithium interactions, the resulting plasma behavior, and the potential mechanisms behind this perceived helium pumping. |
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JP11.00020: Zapdos-CRANE implementation of a lithium vapor shielding model Rabel Rizkallah, Aveek S Kapat, Shane Keniley, Davide Curreli, university E illinois
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JP11.00021: Liquid Lithium Target for High Energy Neutron Generation Steven Stemmley, Cody Moynihan, David N Ruzic Liquid lithium has gained increasing interest as a plasma facing component because of observed enhancement in plasma performance. Most notably, increases in temperature and core density. The Liquid Metal Infused Trench (LiMIT) concept, developed at the University of Illinois, has demonstrated successful performance under fusion relevant conditions in the EAST tokamak and in Magnum PSI with heat fluxes up to 8 MW/m2 and 3 MW/m2, respectively. Recently, this concept has been extended to create compact, self-flowing liquid lithium targets for beam-target fusion neutron generators, which can produce heat fluxes on the order of 10’s to 100’s of MW/m2 due to their small spot size. The liquid lithium surface acts as a self-healing plasma facing material and allows for the production of fusion relevant neutron spectra without tritium for materials testing by utilizing the Li-7(d,n) and D(d,n) reactions. Initial experiments, where a temperature gradient was imposed only via cooling, peak velocities of 16 ± 4 cm/s were observed. Expected yields of this system are 107 n/s for 13.5 MeV neutrons and 108 n/s for 2.45 MeV neutrons. Neutron measurements have been made via a deuterated stilbene scintillator. Results involving the lithium flow and the neutron measurements will be presented. |
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JP11.00022: Lithium Compatibility with Metallic and Coated Substrates for Nuclear Fusion Applications Cody Moynihan, Steven Stemmley, Nick R Schwartz, Brady Moore, Oren Yang, Kristin Skrecky, Joerg Zimmermann, David N Ruzic Lithium has the ability to improve plasma performance, but its application is often limited by material compatibility issues. Corrosion of useful materials along with wettability concerns pose challenges for the widespread use of lithium. The University of Illinois (UIUC) and General Fusion have been working to study and overcome these issues. A dynamic corrosion testbed has been constructed to allow for rotation of samples submerged in lithium for extended periods. Material properties are observed before and after lithium exposure via 3D confocal microscopy and tensile testing. Up to now, many common materials have been tested at UIUC, including titaniums, steels, and stainless steels. Testing of advanced materials, such as Inconels, coated substrates, and 3D printed alloys is ongoing. With our experience in plasma coatings, we look to develop coatings which can protect important incompatible materials, such as copper, from lithium attack. The ability to use lithium with previously unusable materials and in 3D printed geometries will open up many pathways for lithium use in fusion devices. Along with material corrosion, wetting behavior is being investigated by measuring lithium droplet contact angles on substrates. Preliminary results indicate the ability to use yttria coatings to prevent wetting of insulators, however, coating reactions seem to occur. Work is ongoing to determine the wetting behavior of coated and surface modified stainless steels. |
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JP11.00023: Upgrade of SLiC spherical tokamak with dynamic liquid lithium free surface: Li purity control and measurement Stephen J Howard, Don Froese, Wade Zawalski, Kelly Epp, Kristin Skrecky, Alex Mossman The SLiC spherical tokamak experiment has been upgraded to handle a larger total Li inventory (from 3 L to now 15 L) with a recirculating 2-chamber loop that adds the ability to drain and fill the plasma vessel from two separate points. In previous experiments with a single drain/fill port and smaller capacity storage tanks we observed a thin slag layer develop on the surface of the Li puddle due to interaction with plasma hydrogen and other impurity gases. This slag layer persisted even during vigorous Li nonlinear wave motion and its presence may degrade plasma performance. The upgrade provides a way to maintain a pure Li surface through incremental recirculation, as well as collect Li samples for composition analysis. A first round of XPS and IGF analysis showed that the slag was mostly LiOH with lesser amounts of LiH, various carbon compounds, and some NH3. Trace elements were characterized by ICP mass spectroscopy. The slag layer may also be partially responsible for some Li droplet ejection mechanisms, which are being studied within SLiC. The upgrade is also enabling SLiC to operate as a diagnostic testbed for the upcoming FDP device (Fusion Demonstration Plant) where we will need AXUV, Thomson Scattering, optical Zeff measurements to operate in the presence of a dynamic free surface of liquid Li. Lastly, the increased Li inventory will allow deeper Li in the plasma vessel; observing the wave motion with high speed video will benchmark corresponding MHD-CFD simulations over a wider range of parameters. |
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JP11.00024: Understanding of Liquid Lithium Wettability in Porous Tungsten Fusion Plasma Facing Components Sara Kolecki, JP Allain, Camilo Jaramilo, Martin Nieto, Matthew S Parsons, Camila López Pérez, Carli S Smith Exposure of solid plasma-facing components (PFCs) to high irradiation conditions in fusion reactors leads to significant erosion and re-deposition under high-duty cycle conditions. High heat and particle flux can also undermine structural properties of PFCs such as fracture strength and creep rate. Liquid metal (LM) PFCs may be a practical alternative due to their ability to continually replenish material. Their finite residence time helps them tolerate both steady-state and transient heat fluxes within fusion reactors. However, the generation of thin liquid films of low-Z materials has been difficult due to poor adhesion and high surface tension. The work presented here explores the use of nano- and meso-porous substrates as an alternative to improve wetting using capillarity-driven effects such as: imbibition, percolation and wicking. Liquid lithium will be applied to tungsten substrates fabricated by atmospheric plasma spray and field-assisted/spark plasma sintering with an in-vacuo lithium dropper in the IGNIS-2 facility at Penn State's Radiation Surface Science and Engineering Lab. Wettability of liquid Li and porous tungsten samples will be imaged and video recorded in-situ at surface temperatures up to 400 C. Wetting angles will be measured to determine which tungsten substrates and surface microstructures are the most wettable by Liquid Li coatings. |
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JP11.00025: Angular distribution of sputtered and reflected species of the solid and liquid lithium surfaces by deuterium impact 1 Predrag Krstic Molecular dynamics simulations of sputtering and reflection of the liquid (500K), and of the solid (300K) crystalline and amorphous lithium surfaces by deuterium in range of impact angles of 0-87o and energies 1-100eV were performed using REAX force field in combination with electronegativity equalization method. The reflection and sputtering probabilities have a pronounced minimum at perpendicular impact, and then increase toward the larger angles with the gradient which is a function of impact energy. Comparison with available experiments and calculation is shown. |
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JP11.00026: Progress on the liquid metal 'divertorlets' concept: experiments and simulations Francisco J Saenz, Zhen Sun, Egemen Kolemen The liquid metal (LM) plasma-facing component (PFC) is one of the most promising ways to realize a PFC capable of operating for long periods. Concept designs called ‘Divertorlets’ have been presented as a non-evaporative liquid metal solution for heat removal and low-recycling regime operation[1]. Toroidal divertorlets utilize adjacent narrow channels, separated by slats, along the magnetic direction with alternating vertical velocity. Interconnecting rods (significantly more conductive than the LM) within every other channel partially remove current from the liquid metal in the channels they pass through. Differences in current density between channels lead to J × B pumping. |
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JP11.00027: Magnetohydrodynamic Effects of a Gradient Magnetic Field on Liquid Metal Flows Brian R Wynne, Egemen Kolemen The liquid metal divertor approach shows promise for being able to withstand high heat and particle fluxes using a self healing surface, and is an alternative to the traditional solid divertor. Liquid metals have beneficial properties such as high thermal and electrical conductivities, which are necessary for efficient heat removal. We aim to improve the understanding of the effect of magnetic gradient field on liquid metal channel flow and explain magnetohydrodynamic (MHD) phenomena. Current considerations include the MHD drag opposing liquid motion, induced electrical currents, Lorentz force, and understanding the velocity distribution. The change in magnetic field with time has shown a liquid jump, but in a tokamak where the toroidal magnetic field is steady state, the change in magnetic field with position needs to be addressed. Experimental and numerical results are presented on the magnetic field gradient, with experiments performed at the LMX-U facility at PPPL. |
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JP11.00028: Dynamic response of liquid metal free surfaces to localized pulsed current Daniel P Weber, Colin S Adams We present results from an experimental campaign to examine the MHD response of a liquid metal free surface to localized pulsed currents (10—100 kA) and the resulting magnetic fields parallel to the free surface (2—20 T). An LC pulse forming network (PFN) delivers a current pulse through a suspended wire (3.175 mm diameter) into a pool of liquid tin-bismuth (42/58% composition by mass). An estimation of the skin depth suggests that the current is conducted radially along the liquid surface to the walls of the vacuum chamber and returned to ground. The PFN current and liquid metal surface behavior are recorded and compared to MHD simulations, theoretical approximations, and circuit models. The current pulse is shown to produce an annular jet of liquid metal near the suspended wire followed by radially-propagating waves in the pool thereafter. Experiments have characterized the sensitivity of jet velocity and current pulse amplitude to the liquid metal depth and charge transfer from the PFN. |
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JP11.00029: Design of the MPEX Plasma Production and Ion Cyclotron Heating Systems Richard H Goulding, Michael C Kaufman, Jeff D Bryan, J S Dixon, Rob T Haas, Cornwall H Lau, Kirby G Logan, Arnold Lumsdaine, Juergen Rapp, Justin R Weinmeister Steady-state plasma production and ion heating in the MPEX (Material Plasma Exposure eXperiment) are both achieved using RF based systems. High density plasmas are created by a Helicon plasma source coupling power of up to 175 kW at 13.56 MHz through a water-cooled cylindrical vacuum window via an external quarter-turn helical antenna. Ions are heated using fundamental ion cyclotron heating (ICH) in a “magnetic beach” configuration, coupling up to 310 kW at 4-9 MHz through a similar window, with waves coupled by a pair of phased half-turn helical antennas. The designs of the launchers, feed and matching networks, and vacuum windows will be described. The plasma coupling and predicted input impedances for both launchers has been investigated using 3-D COMSOL models that include accurate magnetic field and RF-relevant antenna geometries. For the ICH case, finite electron temperature effects previously seen to be important at MPEX-relevant plasma densities1 are included. These results have been used together with other data and modeling to investigate power handling of the various components. |
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JP11.00030: Overview of the final design of the diagnostic suite for MPEX Theodore M Biewer, T Bjorholm, Juan F Caneses, Drew B Elliott, Travis K Gray, W Sides The Material Plasma Exposure eXperiment (MPEX) is a planned steady-state device at ORNL that will be used to study plasma-material interactions to advance the progress of engineered materials for the plasma facing components of fusion reactors. The final design of MPEX will soon be reviewed, including the diagnostic suite of instrumentation. Similar to other fusion-relevant devices, MPEX diagnostics will serve a variety of roles: machine protection, basic operation, advanced plasma control, and scientific utilization. The diagnostic suite at the preliminary design stage includes: Thomson scattering, optical emission spectroscopy, interferometers, visible and infra-red camera imaging, pyrometers, microwave diodes, bolometry, pressure gauges, residual gas analysis, and in vacuo surface analysis techniques. MPEX diagnostics will be implemented in a staged approach; Phase I diagnostics are those necessary to meet key performance parameters, while Phase II diagnostics are those necessary for the initial scientific utilization of MPEX. It is envisioned that Phase II diagnostics will be implemented in collaboration with institutions outside of ORNL. This presentation will give an overview of the planned diagnostic layout for MPEX. |
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JP11.00031: Modeling of Impurity Sourcing and Transport from High-Temperature Silicon Carbide Walls for Next-Step Tokamaks Tyler Abrams, Gregory Sinclair Simulations of a DIII-D size tokamak with high-temperature silicon carbide (SiC) walls demonstrate reduced plasma-facing component (PFC) erosion rates and upstream impurity accumulation relative to all-graphite PFCs. The total erosion of SiC is reduced by 10× relative to graphite at a divertor surface temperature 800 K. The upstream impurity content also decreases from 2.4% to 0.7% but the higher mass of Si implies similar values of Z-effective (~1.5) between the two cases. Impurity source rates and upstream density decrease at 1000-1200 K for graphite PFCs but not for the SiC cases since most of the erosion is via physical sputtering. Background plasmas were generated with the SOLPS-ITER code package using the DIII-D geometry (3 MW heating power) and then coupled to the DIVIMP impurity transport model. Inclusion of drifts in the favorable B×▽B direction results in minimal changes to the divertor density but increases upstream impurity densities by a factor of 2× due to changes in the parallel force balance. Results are sensitive to the surface temperature of both the inner and outer targets but not the main walls. Parameter scans to higher heating power and in the unfavorable B×▽B drift direction will also be presented. |
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JP11.00032: GITR Simulations of Ion Impacts on the DIII-D DiMES Divertor Sample Targets Alyssa L Hayes, Timothy Younkin, Jerome Guterl, Ane Lasa, Shota Abe, Charles H Skinner, Brian D Wirth GITR is a Monte Carlo code that models the gross and net erosion of PFCs, and the re-distribution of eroded impurities. [1] We used GITR to evaluate the effect of incident IADs at the divertor surface in specifically designed DiMES measurements on DIII-D. |
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JP11.00033: Model predictive control of boundary plasmas using reduced models derived from SOLPS-ITER Jeremy D Lore, Sebastian De Pascuale, Paul Laiu, Birdy Phathanapirom, Steven L Brunton, John Canik, Sacit Cetiner, Nathan Kutz, Peter C Stangeby Time-dependent simulations of the tokamak boundary plasma are performed using the SOLPS-ITER transport code to develop reduced models and model-predictive control (MPC) of the upstream and divertor conditions actuated by main ion and impurity gas puff. The reduced models are based on DMD and SINDy methods, which are data-driven algorithms that extract dynamic behavior to describe the underlying physical system. With DMD, the time evolution is described by discrete operators, while SINDy results in a sparse set of coupled ordinary differential equations. In either case, the model is used to predict the evolution of the current plasma state over a rolling time horizon and determine an optimal actuation sequence to best produce a target trajectory, subject to constraints. Feed-forward MPC actuation sequences input to SOLPS using a DIII-D configuration have been found to agree well with a target density trajectory. When prediction error exceeds a prescribed threshold the model can be updated using past data over a set time window. The MPC method is being implemented into an efficient module that can be called from SOLPS as an online controller. The reduced models are also compared to analytic results and data-mined correlations extracted from simulation and experimental data. |
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JP11.00034: Observation and analysis of fast-inner-target directed parallel flows during the DIII-D isotopic methane injection experiments Shawn Zamperini, Jacob Nichols, E.A. Unterberg, Jonah D Duran, David C Donovan, Dmitry L Rudakov, Kirtan M Davda, Jun Ren, Peter C Stangeby, Tyler Abrams A set of highly diagnosed isotopic methane experiments were recently performed on DIII-D to study low-Z impurity transport in the scrape off layer (SOL). A toroidally symmetric injection of 13CD4 was performed near the outer target, from which the 13C migrated through the SOL and deposited on collector probes inserted at the plasma crown and outboard midplane. The experimental conditions covered a wide range of L-mode operating parameters by varying the plasma density (ne = 2.5-5.0 m3) and injected power (Pinj = 2.5-4.5 MW, PSOL = 2.0-3.5 MW), and operating in both BT directions. Reciprocating Mach probes provided radial profiles of the plasma density, temperature and parallel flow speeds. The expected flow patterns in the crown of fast inner-target-directed flow in the favorable BT direction and relatively stagnant flow in the unfavorable BT direction were measured. Recent studies of high-Z impurity SOL transport demonstrated the controlling role of parallel flows, and this study will investigate if the same conclusions hold for low-Z impurity transport. The range of Mach probe measurements paired with collector probe deposition profiles will enable study of the impact of parallel flows on near-SOL impurity accumulation, as well as the primary physics drivers behind the fast inner-target-directed parallel flows. |
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JP11.00035: Post-mortem surface chemistry analysis of boronized graphite PFC samples and their links to PMI behavior in NSTX-U Camila Lopez Perez, Hanna Schamis, Jean Paul Allain In the 2015-2016 experimental campaign the National Spherical Torus Experiment Upgrade (NSTX-U) used ATJ -graphite as a first wall and divertor material. Wall conditioning was completed with deuterated trimethylboron (d-TMB). Post-mortem samples taken from graphite tiles extracted from various locations in the NSTX-U divertor region after the campaign were analyzed at the IGNIS (Ion-Gas-Neutral Interactions with Surfaces) facility at UIUC using X-ray Photoelectron Spectroscopy (XPS). According to the XPS analysis, samples contain on average 15-30% B. At Penn State, additional post-mortem samples are analyzed using both XPS and Scanning Auger Electron Spectroscopy (AES) to establish an elemental mapping and chemical characterization of the extracted tiles. In addition, samples of varying B concentration will then be exposed to high flux D+ ions, mimicking plasma material interactions in a tokamak, and later analyzed with XPS and Thermal Desorption Spectroscopy (TDS) to decipher PMI behavior linked to NSTX-U plasma operation. XPS and TDS will also be used to investigate the effects of the D+ irradiation on the surface chemistry and retention of the samples. The acquisition of data through XPS, AES and TDS will further investigate the chemical composition of the tiles after deuterium exposure. |
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JP11.00036: Surface chemistry and morphology studies of boronized tungsten samples from WEST Hanna Schamis, Camila Lopez Perez, Jean Paul Allain WEST is a long-pulse tokamak with a full tungsten first wall and divertor which are conditioned using boron. After the C4 campaign, tiles were extracted from the tokamak in order to perform post-mortem analyses. The analyses will be performed at Penn State with techniques such as depth-profile X-ray Photoelectron Spectroscopy (XPS), Scanning Auger Electron Spectroscopy, Scanning Electron Microscopy, and 3D optical profilometry. With XPS, the chemical composition and stoichiometry of the top 10 nm of a material can be analyzed, while depth profiling enables characterization of compositions from the surface towards the bulk of the material. The focus of these post-mortem analyses will be on characterizing the chemistry and morphology of reconstituted (or redeposited) layers. Reconstituted layers form after repeated high particle and heat flux exposure in tokamak environments. The characteristics of these WEST reconstituted layers will be compared to those of lab-grown boron and tungsten mixed material deposited films, in order to evaluate new ways to study these complex materials. These mixed material films will be deposited and characterized in the new IGNIS-2 facility at Penn State. |
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JP11.00037: An in-situ and in-vivo characterization facility for Ion-Gas-Neutral Interactions with Surfaces (IGNIS-2) under fusion-relevant vacuum conditions Ethan Kunz, Jean Paul Allain, Matthew Fredd, Camilo Jaramillo, Sara Kolecki, Camila López Pérez, Matthew S Parsons, Martin Nieto-Pérez, Hanna Schamis, Carli S Smith Future facilities studying plasma-facing materials (PFMs) for use as tokamak first wall materials must simulate key aspects of the fusion environment and analyze surface morphology and chemistry of samples without exposure to ambient. Fusion-relevant vacuum conditions are critical in ex-vessel facilities designed to qualify PFMs including background ambient pressure (partial H2O), working gas pressure (D2 at mTorr ranges), wall conditioning (e.g. B, Li) and radiative gas shielding (e.g. N, Ne). |
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JP11.00038: Simulations of the plasma-wall transition with oblique magnetic field, collisions, and electron emission Michael D Campanell, Alex Friedman, David P Grote Secondary, thermionic and photoelectron emission are predicted to alter the sheath potential, heat transport and sputtering at plasma-facing surfaces such as tokamak divertor plates and probes. Although a number of publications have described studies of emitting sheaths in unmagnetized plasmas, only a few studies have included oblique magnetic fields, typically without collisions. Unmagnetized sheath simulations show that collisions cause ion trapping in the reversed-field region near an emitting surface. Thus it is important to consider how collisions affect the magnetized, emissive plasma sheath, where electron and ion gyromotions near the surface play a key role. By adapting the WarpX particle-in-cell simulation framework developed jointly by LBNL and LLNL we developed a simulation code that captures the combined effects of collisions, magnetic fields and electron emission on the plasma-wall interaction. Different regimes of sheath behavior are observed as the governing parameters (such as particle temperatures, B field inclination angle, collision mean free paths, and emitted flux) are varied. |
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JP11.00039: Particle-in-Cell study of impurity production from RF sheaths in front of ICRH actuators Mikhail Rezazadeh, Moutaz Elias, Logan Meredith, Jon T Drobny, Davide Curreli The radio-frequency plasma sheath formed in front of an Ion Cyclotron Resonance Heating (ICRH) antenna is responsible for significant ion acceleration and consequent material sputtering and impurity emission. In order to characterize the emission process, we performed a set of parametric simulations using two kinetic codes, the hPIC2 Particle-in-Cell and the RustBCA sputtering code. hPIC2 solved the time-dependent structure of the radio-frequency sheath, capturing both RF sheath rectification and the time modulation of the plasma potential. hPIC2 provided the time-dependent energy-angle distributions of the ions impacting on the surface, which were then fed as an input to the RustBCA sputtering code, in order to produce RF-phase-resolved distributions of sputtered impurities. From the analysis of the results we observed that the impurity emission is highly non-linear along the RF cycle, mainly because of the large non-linearities of the sputtering behavior as a function of energy and angle of the impacting ions. The effect on the time-integrated fluxes of magnetic field inclination, RF voltage, density, and plasma temperature is highlighted. |
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JP11.00040: Application of the Hybrid Particle-In-Cell code: PRO++OMG to simulate plasmas in open magnetic geometries Atul Kumar, Juan F Caneses In this work, the hybrid PIC code: PRO++OMG is applied to study plasma transport in two different open magnetic geometries. The analyses include the effects of: (1) finite fully-absorbing boundaries for the particles, (2) volumetric particle sources, (3) Fokker-Plank Collision operator and (4) Radio-Frequency (RF) heating. RF heating on a divertor simulator: Material Plasma Exposure eXperiment (MPEX) is studied to understand ion heating using fundamental ion cyclotron resonance and its associated parallel transport. It is found that RF heating can lead to anisotropic ion distributions at the target. Furthermore, the effect of Neutral Beam Injection (NBI) on the parallel electric field and plasma confinement in an Axisymmetric Magnetic mirror geometry has been investigated. It is found that the presence of NBI enhances the confinement of warm ions in a mirror plasma system. |
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JP11.00041: Development of an absorbing first wall interface for small fusion devices Danah Velez, Mykola Ialovega, Marcos Navarro Gonzalez, Oliver Schmitz, Cary B Forest Tantalum (Ta) is known for its hydrogen storage property, high melting point and favorable resistance to sputtering. These properties bring forth interest in Ta as a plasma-facing material (PFM) for small-scale fusion devices which need to operate at low neutral pressures. Tantalum is foreseen as a PFM for the Wisconsin HTS Axisymmetric Mirror (WHAM). WHAM is a compact, high-field mirror design. Explorations of Ta are underway to investigate its potential as a neutral getter to improve plasma performance. This study aims to test whether Ta deposited by cold spraying can withstand high heat loads, particle erosion and effectively retain hydrogen isotopes. In these experiments, stainless steel rods were cold sprayed with Ta powder with five spraying conditions where temperature and proportion of carrying gasses (N2/He) were varied. The samples are being prepared for testing via surface and bulk diagnostics before and after deuterium plasma exposure in the PSI-2 device. This will allow for examination of the effects of the particle and heat fluxes on the material’s retention capabilities and physical properties. Future development of the cold spraying technique may allow for its use in fusion devices with in-situ deposition of various materials on the surfaces of plasma-facing components. |
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JP11.00042: Optimizing fusion power balance using HTS magnets, negative triangularity, and high-Z impurities Haley Wilson, Andrew O Nelson, Carlos Paz-Soldan, Dennis G Whyte A well-studied configuration for net fusion power is the steady-state conventional aspect ratio advanced tokamak that uses D-T fuel and superconducting magnets. Recent advances in high temperature superconductor (HTS) magnet technology have encouraged the exploration of toroidal plasmas that deviate from this model. In particular, we use 0-D and 1-D reactor models to explore the benefits of a pulsed approach and using advanced fuel cycles, both of which offer potential physics and engineering simplification. Recent research also shows that tokamaks with negative triangularity configurations can exhibit improved confinement. We adapted a computational tokamak reactor model[1] to allow leverage of the triangularity of the plasma and density profile of seeded high-Z impurities, as well as other more typical plasma parameters. With this model, we explore the effect of HTS technology, advanced fuel cycles, negative triangularity, and seeded impurities on fusion power balance. |
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JP11.00043: Scoping studies of plasma detachment in long-leg divertor geometries Rebecca L Masline, Sergei Krasheninnikov A new class of magnetic divertor geometries with long poloidal legs have been proposed as a solution to handle the extreme power exhaust projected for future tokamak reactors. At present, it is not clear how the existing understanding of the underlying physics of the detached divertor regime will translate to these new geometries. To assess the physics of plasma detachment in these newly-proposed configurations, scoping studies of tokamak plasmas in a long-leg divertor geometry are performed using 2D plasma edge transport codes. The model includes a standard leg divertor at the inner target and a narrow, tightly-baffled long poloidal leg divertor at the outer target. A scan of plasma parameters is generated by using a so-called “closed gas box” particle model and increasing total particle count with fixed input power to assess the physics of the transition to detachment in the long-leg regime. Simulations of pure deuterium plasmas show that the long-legged outer divertor plasma demonstrate onset of detachment in an isolated flux tube at similar criterion to that of standard divertors [S. I. Krasheninnikov, A. Kukushkin, A. Pshenov, Phys. Plasmas 23, 055602 (2016)]. Strong ionization at the outer divertor target and an increase in flux to the side walls of the long divertor leg are also observed. |
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JP11.00044: Non-Coronal radiation enhancement in advanced divertor geometries with power scaling to ITER Jonathan Roeltgen, Mike Kotshenreuther, Swadesh M Mahajan, Hames Harrison, David Moulton, Zhong-Ping Chen Through SOLPS-ITER simulations of DIII-D and MAST-U, an X-divertor (XD) on DIII-D and a super X-divertor (SXD) on MAST-U were shown to have increased emissivity PRad/(nenI) than corresponding standard divertors (SD) at similar degrees of partial detachment, specifically a target temperature of 2eV just outside the separatrix. The XD has a higher emissivity at higher input powers, unlike the SD which has a lower emissivity at higher input powers. This comparison of emissivity and its dependence on field line angles and input power is extended to ITER and DEMO (with nitrogen as the impurity) using a 1D model, where low field line angles (such as seen in an XD) continue to perform better. The reasons behind the increased emissivity in the DIII-D XD and SXD are analyzed using a simple 0D transport model. From the transport model, it is seen that a major cause of the increased emissivity in the XD and SXD over the SDs is a greater neutral deuterium density, which allows for greater charge exchange with carbon. |
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JP11.00045: Electron-impact ionization and excitation of Si+ for applications in laboratory and astrophysical plasmas Andrew P White, Connor P Ballance, David A Ennis, Stuart D Loch Accurate electron-impact data for Si ions is essential for determining Si abundances in astrophysics and erosion characteristics for laboratory plasma facing components. A new calculation of electron-impact data for Si+ using the R-matrix with pseudo-states (RMPS) method has been carried out. Both ground state and excited state ionization cross sections have been calculated. The ground state ionization cross section shows excellent agreement with crossed beams experimental measurements; however, the authors are aware of no other data with which to compare the excited state ionization cross sections. Excited state ionization cross sections are significant because they have proven essential in existing plasma diagnostics for other species (e.g. Li, Be, B, W). Excitation calculations have also been performed, which are used to generate atomic coefficients representing “ionizations per photon” (S/XB) which are needed for erosion diagnostics of plasma facing components. Generalized atomic coefficients for Si+ have particular relevance for Si as a plasma facing component of fusion relevant experiments. |
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JP11.00046: Effects of secondary runaway electron generation due to large-angle collisions on runaway electron mitigation via material injection* Matthew T Beidler, Diego Del-Castillo-Negrete, Daisuke Shiraki The leading candidate for disruption and runaway electron (RE) mitigation in ITER and future devices is massive material injection. A consequence of increasing the electron density is an increase of secondary RE generation from large-angle collisions of primary REs with the background plasma. In addition to the initial material injection used to trigger a disruption, secondary RE generation plays a critical role during post-disruption material injection used to mitigate the effects of the RE beam. In both cases, large induced electric fields accelerate REs, resulting in a magnetic to kinetic energy conversion. The present work improves recent modeling of RE mitigation in Ref. [1] by including a secondary RE source in the KORC code. Presented simulations will evaluate the effects of secondary RE generation across several experimental scenarios and estimate the energy deposited to the device walls resulting from the increased magnetic to kinetic energy conversion. |
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JP11.00047: Polarization of synchrotron emission from runaway electrons Diego Del-Castillo-Negrete Runaway electrons (RE) can be produced during magnetic disruptions and, if not avoided or mitigated, they can damage the plasma facing components of fusion reactors. A key element to assess this damage is the accurate modeling of the RE spatial and phase-space distribution. Synchrotron emission (SE) is a valuable experimental diagnostic commonly used to estimate the RE beam size, energy, and pitch angle. Motivated by this, in Ref.[1] we developed a numerical SE synthetic diagnostic including full-orbit effects and taking into account the spectral and angular distribution of the SE, as well as optical and geometric properties of the camera. Based on this work, we present a new synthetic diagnostic that incorporates more efficient orbit integrator and Monte-Carlo sampling algorithms and, most importantly, SE polarization effects. Numerical simulations quantifying the dependence of the vertically and horizontally polarized radiation intensities on the pitch angle are discussed. The dependence of the radiation intensity and image shape on the wavelength and polarization direction are also studied for different energy and pitch angle distributions. |
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JP11.00048: Runaway electron dynamics in MST tokamak plasmas measured by a versatile multi-energy SXR camera Luis F Delgado-Aparicio, Noah C Hurst, Patrick D VanMeter, Abdulgader Almagri, Brett E Chapman, Cary B Forest, John P Wallace, Karsten J McCollam, Daniel J Den Hartog, Tullio Barbui, Oulfa Chellai, Novimir A Pablant, Kenneth W Hill, Manfred L Bitter, Masayuki Ono, Brentley C Stratton A versatile multi-energy soft x-ray (SXR) pinhole camera has been designed, built, and deployed for the Madison Symmetric Torus (MST) to aid the study of particle and thermal transport, as well as MHD stability physics. A novel application detecting the birth of runaway electrons (REs) measuring its time- and spatial-dependence during the linear and exponential growth phases has recently been demonstrated. The ME-SXR pin-hole camera provides unprecedented improvement in signal-to-noise-ratio, early-detection, imaging and energy discrimination at Ephoton/Te,0~20-200. REs are generated at the MST in steady tokamak plasmas with low current and toroidal magnetic field obtaining core temperatures and densities of the order of 0.1 keV and <0.1×1019m-3, respectively. Density thresholds for both runaway electron onset and suppression are determined with simple variations in gas puffing. A detail scan of resonant magnetic perturbations intensity (RMPs, with poloidal mode number m=3) also resulted in the suppression of REs consistent with the appearance of a broad region of stochasticity. This work is supported by the DoE as a collaboration between PPPL and WiPPL. |
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JP11.00049: LHCD Suppression of Impurity-Induced RE Current Quench in C-Mod Simulated with CQL3D-GENRAY Robert W Harvey, Yuri V Petrov, Alexander Pigarov, Paul T Bonoli, Syun'ichi Shiraiwa, Paul B Parks
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JP11.00050: Simulation of Runaway Electron Production with CQL3D coupled to NIMROD Yuri V Petrov, Robert W Harvey, Charlson C Kim, Lang L Lao The CQL3D bounce-averaged Fokker-Planck (FP) code [1,2] is used to simulate Runaway Electron (RE) production in DIII-D thermal quench experiments with Neon shattered pellet injection. A one-way coupling has been achieved between the 3D extended MHD code NIMROD and CQL3D; the time-dependent data on plasma profiles (Ohmic current density, temperatures, toroidal electric field, densities of all ionization states of Neon, etc.) is read from NIMROD and mapped to the CQL3D grid. CQL3D then advances the FP solution for electrons over the same time range as NIMROD. As REs appear, the toroidal electric field used in CQL3D is adjusted by an internal feedback procedure to maintain a nearly constant current density during the thermal quench. Early results without radial transport of REs show a modest production of RE current. The distribution functions reveal an evolving velocity-dependent bump-on-tail feature. Time-dependent magnetic field fluctuation data from NIMROD is being used by CQL3D to calculate the effects of RE radial transport. |
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JP11.00051: Self-consistent modeling of disrupted plasma and runaway electrons using the coupled DTRAN/CQL3D codes Alexander Pigarov, Robert W Harvey, Yuri V Petrov CompX is developing an integrated code, in which kinetic 2V-1.5D Fokker-Planck code CQL3D is coupled to new macroscopic transport code DTRAN (Disruption TRANsport). Here we report on progress in development of DTRAN as multispecies, 1.5D magnetic-flux-surface averaged plasma parameters, diffusive-convective transport code, which 1) solves a system of many strongly coupled equations for plasma densities/temperatures, ionization states of impurity species, neutral atoms, molecules, and for magnetic fluxes and electric currents; 2) incorporates quasi-static magnetic geometry evolution based on GSE; 3) solves equations for impurity pellet propagation, ablation, and assimilation of an emergent impurity cloud by the thermal plasma, and for the subsequent MGI pulses. The modeled disruption mitigation scenario causes radiative collapse of plasma down to a few eV and lower, changes magnetic configuration, enhances PMI processes, modifies parallel electric field, and can result in a highly non-Maxwellian time-dependent RE distribution calculated by CQL3D featuring a relativistic RE tail, which in turn affects the plasma current, radiation and ionization degree. Initial results on these comprehensive coupled processes modeling with DTRAN/CQL3D will be presented and discussed. Research supported by DOE grant DE-FG02-04ER54744 |
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JP11.00052: Runaway studies in disruptions with partial current relaxation Istvan Pusztai, Mathias Hoppe, Tunde M Fulop The safe operation of tokamak reactors requires a reliable modeling capability of disruptions, and in particular the spatio-temporal dynamics of associated runaway electron currents. To explore the vast parameter space characterizing off-normal events, computationally efficient reduced models are needed. Such models are necessarily of low dimensionality. Therefore, accounting for fast magnetic reconnection - driving current profile relaxation, as well as a rapid transport of heat and energetic particles - has posed a major challenge. Using the implementation of the mean field helicity transport model of [A. H. Boozer 2018 Nucl. Fusion 58 036006] in the new 1D2P disruption runaway modeling code DREAM [M Hoppe et al 2021 Comp. Phys. Comm.], we calculate the dynamics of runaway electrons in scenarios where skin currents are induced at the boundary of stochastic and intact magnetic field line regions, accompanying fast reconnection in part of the plasma. We find scenarios where significant reverse runaway skin currents are generated in the plasma edge, which may act as a seed for a regular (forward) edge-localized runaway current, when helicity transport is low in the edge. |
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JP11.00053: What will ITER do about the large islands that trigger disruptions? Allan Reiman, Richard Nies, Nathaniel J Fisch Experience with disruptions in JET suggests that many of the disruptions in ITER will be preceded by the growth of large islands. 95% of the disruptions in JET have been preceded by locked modes [1]. Analysis of disruption data on JET has found that islands grew to 30% of the minor radius before a disruption was triggered [2]. The islands grow on a resistive time scale. It will be desirable to deal with these islands before they trigger a mitigation event. However, the ECCD island stabilization capability on ITER has been optimized for the stabilization of small islands produced by neoclassical tearing modes. With the toroidal launch angle of the upper launchers fixed at 20 degrees, they are not well suited for the stabilization of large islands produced by other off-normal events. It will be desirable to make the mirrors of the upper launchers steerable in the toroidal angle. This will be particularly useful for increasing the current drive efficiency when the q=2 surface shifts inward. Nonlinear effects will be significant [3]. They can be used to advantage but must in any case be accounted for in aiming the EC to avoid degradation of the stabilization capability. |
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JP11.00054: Incorporation and Verification of a Fluid Model for Runaway Electrons in NIMROD. Alexandre Sainterme, C. R. Sovinec, S. C. Jardin, Chen Zhao, Ge Wang A reduced fluid model for runaway electrons (REs) is incorporated into the NIMROD code. REs are treated as a distinct fluid species that flows with a velocity consisting of a large prescribed parallel component and a perpendicular component arising from E cross B drift. There is both a volumetric source density for the runaway species given by the local background density and parallel electric field via the Dreicer mechanism and a volumetric source density representing the avalanche runaway generation. As in the model presented in Bandaru, et al. [PRE 99, 063317(2019)], the RE density evolution couples to the MHD equations via Ohm's law and the momentum evolution in accordance with the assumption that the RE species does not contribute to the resistive electric field. Comparison of numerical results to analytic expressions for simple cases is presented. Comparisons of NIMROD results from a test case in which REs are generated via a thermal quench (TQ) to results obtained in Bandaru, et al. serve as a benchmark for the fully coupled nonlinear system. A second benchmark addresses RE production for a simulated TQ of an equilibrium reconstructed from experiment and includes comparison with M3D-C1. |
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JP11.00055: Lagrangian Particle Simulations of Pellets and SPI into Runaway Electron Beam in ITER Roman V Samulyak, Shaohua Yuan, Nizar Naitlho, Eric Nardon, Michael Lehnen Numerical studies of the ablation of pellets and shuttered pellet injection (SPI) fragments into a runaway electron beam in ITER have been performed using the time-dependent pellet ablation code [R. Samulyak at el., Nucl Fusion, 61 (4), 046007 (2021)] based on Lagrangian Particle (LP) method. The code implements low magnetic Reynolds number MHD equations, volumetric heating by runaway electrons, an equation of state with multiple ionization, an ionization by impact model, and a model for grad B drift of the ionized material across the magnetic field. The study of the single fragment ablation quantifies the influence of various factors, in particular the impact ionization by runaway electrons, on long-scale dynamics of the ablated plasma. We show that the grad-B drift prevents the ablated material from penetration deeply into the runaway region. Simulations of the SPI at various values of the tokamak safety factor provide information on global dynamics of the ablated plasma. |
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JP11.00056: Simulation of plateau formation during current quench and MHD instabilities with runaway electrons Chen Zhao, Chang Liu, Stephen C Jardin, Nathaniel M Ferraro, Brendan C Lyons
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JP11.00057: Emis3D: Radiated Power Modeling Following Shattered Pellet Injection Mitigation in JET Benjamin Stein-Lubrano, Ryan Sweeney, Robert S Granetz, Daniele Bonfiglio, Jack Lovell, Eric Nardon Precise values for radiated power during mitigated disruptions are important for predicting the effectiveness of mitigation techniques at preventing damage to future large or high-field tokamaks like ITER and SPARC. Scarcity of diagnostics optimized for disruption radiated power studies forces reducing the dimensionality of the problem when using conventional methods. Plasma radiation during the thermal quench is highly toroidally and poloidally asymmetric and the inferred radiated power is sensitive to the structure. Emis3D is a new approach to resolving the 3D radiation structure from limited diagnostics. It leverages the Cherab modeling framework to generate synthetic measurements of feed forward emissivity models. The underdetermined problem is then addressed by evaluating many possible models to find the group of best-fit solutions, providing a more informed range of possible radiated powers and peaking factors than conventional methods. Discharges from the JET Shattered Pellet Injection database are analyzed using Emis3D and compared with conventional methods. Future work will explore the radiation intensity on individual plasma-facing components in JET. Emis3D also interfaces with 3D MHD codes to better facilitate comparisons of simulation and experiment. |
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JP11.00058: Identifying physical disruption boundaries in Alcator C-Mod using linear Support Vector Machines Andrew Maris, Cristina Rea, Robert S Granetz, Erik Olofsson, Darren T Garnier The threat of disruptions in next-generation tokamaks and future fusion power plants has motivated a broad investigation into disruption avoidance and prediction. Among the various analytical tools applied to the disruption problem, machine learning (ML) has garnered interest for its ability to learn from empirical data and evaluate predictions in real-time. Unfortunately, the black-box nature of many ML algorithms creates uncertainty about their reliability, physicality, and generalizability. Here, we present two approaches to learning physically interpretable disruption boundaries using linear Support Vector Machines (lSVMs): a sum-of-polynomials fit and a power law fit. We demonstrate these approaches on data from C-Mod, examine their physical significance, and discuss their utility as disruption predictors. Future work will apply this approach to data from DIII-D. |
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JP11.00059: Implementation of MHD-mode induced disruption forecaster into the DECAF code Veronika Klevarova, Steven A Sabbagh, John Berkery, Young-Seok Park, Yanzheng Jiang, J Riqueze, Jalal Butt, Jun-Gyo Bak, Jayhyun Kim, Jinseok Ko, Jongha Lee, Si-Woo Yoon, Keith Erickson Timely detection and prevention of plasma disruptions, leading to abrupt losses of the plasma confinement, is a prerequisite for successful operation of next-step tokamaks such as ITER. The Disruption Event Characterization and Forecasting (DECAF) code [1] implements algorithms that aim at resolving, characterizing and forecasting the chain of events that precede the disruption. One such event is onset of an MHD mode that triggers the plasma deconfinement once it reaches a critical amplitude. This amplitude, for modes that are static in the laboratory frame, has been estimated in past work with an empirical formula [2] that was recently validated on multiple devices [3]. Application of this formula thus represents a potentially important ingredient for a forecaster of the disruption onset. The formula’s accuracy will be explored and the underlying physics analyzed using DECAF on a large set of plasmas from several tokamak devices including KSTAR and NSTX. This analysis will serve as an important base for further expansion of offline and real-time DECAF capabilities. |
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JP11.00060: PIXIE3D simulations of nonlinear saturation of MHD modes Ioannis Keramidas, Luis Chacon, Xianzhu Tang The rapid loss of magnetic surfaces and the ensuing onset of |
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JP11.00061: Fast-ion transport optimization using the integrated TGLF-EP+Alpha Alfvén eigenmode transport model Eric M Bass, Cami S Collins, Michael A Van Zeeland, Ronald E Waltz Control of Alvfén eigenmodes (AEs) driven by energetic neutral beam injection (NBI) ions in DIII-D is explored with the TGLF-EP+Alpha model. TGFL-EP+Alpha is a reduced model assuming stiff-transport informed by DIII-D experiments and nonlinear gyrokinetic simulations. Neutron deficit below classical predictions (a proxy for AE transport of fast ions) is experimentally reduced by up to 35% by moving NBI off axis and/or moving electron cyclotron current drive to on-axis. TGLF-EP+Alpha captures these trends, predicting the evolving neutron signal to within 12% and qualitative features of the radius-time AE spectrogram across the entire current ramp. The general utility of TGLF-EP+Alpha is further demonstrated with other DIII-D whole-shot AE validations over a range of AE activity, with neutron predictions within 20% (or much better) across time in multiple AE-dominant and quiet cases. The physics-based TGLF-EP+Alpha model improves over ad hoc energetic particle diffusivity currently used in integrated modeling workflows. It’s inexpensive enough for scenario optimization and validated over a wide parametric range. |
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JP11.00062: Fast Ion Transport Studies in JET in Preparation for DT Experiments Phillip J Bonofiglo, Mario L Podesta, Roscoe B White, Matteo Vallar, Nikolai Gorelenkov, Vasili Kiptily, Viktor Goloborodko, Ed Cecil This presentation reports the efficacy of an energetic particle transport model against saturated kink-modes and sawteeth in JET plasmas. The mode-resonant transport during the internal kink growth phase is compared against the drastic fast ion phase-space redistribution from sawtooth crashes. This report aims to classify and validate the dominant transport mechanism with numerical modeling constrained by experimental measurements. A detailed examination of the fast ion phase-space dependencies, resonances, and induced losses associated with the resonant kink mode and non-resonant sawtooth stochastization transport mechanisms will be presented. Lastly, an initial analysis of alpha particle losses from JET's 2021 T and DT campaign will be presented. The ORBIT-kick model forms the basis of the transport studies with realistic fast ion distributions produced from TRANSP. A recently created sawtooth model within ORBIT and the ideal MHD code NOVA provide the mode structures and properties. The resulting energetic particle transport is validated against experimental loss measurements through the incorporation of a synthetic fast ion loss detector within ORBIT. Additionally, the model is cross-referenced against loss ion scintillator probe and gamma spectroscopy measurements. |
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JP11.00063: Energetic particle diffusion and convection interface in NUBEAM with initial value simulations Marina Gorelenkova, Nikolai Gorelenkov, Mario L Podesta, Vinicius N Duarte, Francesca M Poli, Joshua A Breslau, Jai Sachdev, Alexei Pankin, Laszlo Glant, Gopan Perumpilly A numerical scheme to map 2D diffusion and convection coefficients for energetic particle transport in energy and minor radius to the constant of motion (COM) space is proposed for interfacing the NUBEAM guiding center simulations with different initial value models. Two possibilities are considered: in the first, the fine grid probability density function characterized by parameters that define diffusion and convection on each grid bin; in the second, a straightforward interpolation for the COM variables of interest, canonical momentum and energy, from the diffusion and convection values on a COM grid is proposed. Verification exercises using analytic representation of 2D diffusion coefficients and convective velocities are proposed for the NUBEAM code aiming at the time scales much longer than the characteristic precession motion times. The diffusion/convection kick steps are chosen to allow sufficient diffusion over the time, △t, much longer than their transit steps, τpr, and are examined in this work for the DIII-D test where △t » τpr≈0.5μsec. |
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JP11.00064: A Computational scheme for Quasilinear Diffusion for magnetized fast electrons in a mean field of quasi-particle wave packets. Kun Huang, Michael Abdelmalik, Irene Gamba The space averaged quasi-linear diffusion model for magnetized fast electrons in momentum space results from stimulated emission and absorption of waves packets via wave-particle resonances. The model consists in solving the dynamics of a coupled system of classical kinetic diffusion processes described by the balance equations for electron probability density functions (electron pdf) coupled to the time dynamics on spectral energy waves (quasi-particles) in a quantum process of their resonant interaction. Such description results in a ‘mean field’ model where diffusion coefficients are determined by the local spectral energy density of excited waves whose perturbations depend on flux averages of the electron pdf. |
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JP11.00065: A global quasilinear critical gradient model for Alfven eigenmode transport of energetic particles1 Ronald E Waltz, Eric M Bass -R.E. WALTZ and E.M. BASS, General Atomics. The local critical gradient model (CGM) for the transport of energetic particles (EP) by Alfven eigenmodes (AEs) has been verified by local nonlinear GYRO gyrokinetic simulations[1], validated by DIII-D experiments[2], and used to predict ITER EP confinement loss[3]. A new global quasilinear critical gradient model (GQLCGM) is presented. Global linear GYRO simulations of a DIII-D discharge are advanced in time with the GYRO quasilinear EP transport fluxes fed to an ALPHA-like EP density transport code[3]. The relaxing driving EP density gradient profile is fed-back to GYRO until the most unstable global AE mode reaches a marginal state. A global critical gradient and EP transport profiles with significant large EP orbit effects is obtained and compared to the local CGM. |
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JP11.00066: Shifting and splitting of resonance lines due to dynamical friction in plasmas Vinicius N Duarte, Jeff B Lestz, Nikolai Gorelenkov, Roscoe B White A quasilinear plasma transport theory that incorporates Fokker-Planck dynamical friction (drag) and scattering is self-consistently derived from first principles for an isolated, marginally-unstable mode resonating with an energetic minority species. It is found that drag fundamentally changes the structure of the wave-particle resonance, breaking its symmetry and leading to the shifting and splitting of resonance lines. In contrast, scattering broadens the resonance in a symmetric fashion. Comparison with fully nonlinear simulations shows that the proposed quasilinear system preserves the exact instability saturation amplitude and the corresponding particle redistribution of the fully nonlinear theory. Even though drag is shown to lead to a relatively small resonance shift, it underpins major changes in the redistribution of resonant particles. These findings suggest that drag can play a key role in modeling the energetic particle confinement in future burning fusion plasmas. |
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JP11.00067: Validation and verification of quasi-linear modeling using a single unstable Alfvén mode in DIII-D Nikolai Gorelenkov, Vinicius N Duarte, Michael A Van Zeeland The oscillatory behavior of a single unstable Alfvénic mode observed in DIII-D experiments [Van Zeeland et al, NF'21] excited by suprathermal beam ions is investigated numerically. The goal of such study is to validate the quasilinear methodology used in recently developed Resonance Broadened Quasilinear code RBQ [Gorelenkov et al., PLA'21]. Another goal is to verify RBQ against the fully nonlinear Vlasov code BOT. The excited mode is in the TAE gap, identified using the ideal MHD code NOVA. The comparison helps to understand multiscale intermittencies and oscillations observed in experiments and predicted in simulations [Berk, PRL'92, Gorelenkov et al., PLA'21]. An interplay between the growth, damping rates and the effective scattering frequency in RBQ simulations exhibits a predator-prey behavior of the mode amplitude evolution. Since experiments suggest that the mode remains near marginal stability throughout its evolution, a self-consistent quasilinear framework is employed that embodies collisions and that replicates the same saturation levels predicted by nonlinear theory [Duarte et al, PoP’ 19]. Additionally, beam blip experiments like these exhibit a rapidly changing drive that needs to be factored into simulations. |
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JP11.00068: Reduced quasilinear treatment of energetic electron instabilities in nonuniform plasmas. Dmitrii I Kiramov, Boris Breizman High-frequency kinetic instabilities can enhance scattering of the runaway electrons (REs) dramatically. This wave-induced scattering should be beneficial for RE mitigation. |
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JP11.00069: Excitation of fishbone and beta-induced Alfvén eigenmode and interaction with energetic particles Chang Liu, James J Yang, Stephen C Jardin, Mario L Podesta, Nikolai Gorelenkov, Dylan P Brennan It has been shown that various MHD instabilities can interact with fast ions and affect the confinement of them. Synergy of modes with different poloidal harmonics can enhance the fast ion transport. In this work we used the hybrid-MHD code M3D-C1-K to calculate the excitation of MHD instabilities in existence of energetic particles in both NSTX and DIII-D. Our results show that energetic particles can change the characteristic of excited MHD modes. For equilibrium with minimum q value smaller or close to 1, a fishbone mode can be excited. For equilibrium with minimum q larger than 1.1, the fishbone becomes stable but a beta-induced Alfvén eigenmode (BAE) can be excited instead. The result is consistent with the previous work done using NIMROD, and the frequency of BAE is consistent with the calculation of eigenvalue code NOVA. The excited modes have both m=1 and m=2 components, which can lead to particle resonance happening at different flux surfaces and enhance particle transport. |
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JP11.00070: Regulation of Alfven eigenmodes by microturbulence in fusion plasmas Pengfei Liu, Zhihong Lin, Xishuo Wei, William W Heidbrink, George R McKee, Gyungjin Choi, Javier H Nicolau, Guillaume R Brochard Recent theoretical and experimental studies have suggested possible effects of microturbulence on Alfven eigenmode (AE) saturation and energetic particle (EP) transport in the fusion plasmas. Zonal flows can be nonlinearly generated by, and in turn, suppress both the AE and microturbulence. EP Scattering by the microturbulence can affect phase space dynamics in the nonlinear AE-EP interaction. Unstable AE can also be scattered to shorter wavelength damped modes due to modulation by the microturbulence. |
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JP11.00071: An E & B Gyrokinetic Simulation Model for Alfvén Waves in screw pinch and Tokamak Plasmas Maxwell H Rosen, Zhixin Lu, Matthias Hoelzl The gyrokinetic particle simulation serves as a powerful tool for the studies of transport, nonlinear phenomenon and energetic particle physics in tokamak plasmas. While most gyrokinetic simulations make use of the scalar and vector potentials, a new model has been developed by using the E and B field [1,2]. This method shows excellent performance in a realistic parameter regime of burning plasmas in terms of high values of ??/(Me k⟂2 ??i2). |
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JP11.00072: Efficient evaluation of the EP-driven stability landscape and nonlinear states using Landau closure methods Donald A Spong, William W Heidbrink, Michael A Van Zeeland, Yashika Ghai, Jacobo Varela Rodriguez, Luis Garcia The FAR3d global gyro-Landau moments model provides an efficient kinetically-closed reduced model for energetic particle (EP) – driven instabilities in tokamaks and stellarators. Two examples of this are: (a) the linear eigenvalue structure of the moments equations, allowing rapid scans of multiple unstable modes as parameters/profiles are changed, and (b) the feasibility of long-time scale nonlinear simulations in strong mode coupling regimes. These capabilities are demonstrated based on selected discharges from the DIII-D tokamak. Under (a) we examine a sequence of low-frequency EP-driven instabilities (BAE frequency and below) as the q-profile is varied. Low frequency EP instabilities are of interest due to the increased EP transport they can drive. Under (b) a nonlinearly saturated TAE state is examined with respect to turbulent transport rates, effects of source/sink variations, fast ion critical gradient profiles, and intermittency levels. The simulation of instability-driven fast ion transport and intermittency is an important factor for integrated modeling and performance predictions of future fusion systems. |
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JP11.00073: Serendipity shape functions in NIMROD's delta-f PIC approach to energetic particle physics Trevor V Taylor, Eric D Held, Joseph A Spencer, Scott E Kruger Wave-particle resonances can have significant effects on plasma stability even in the case of small, resonant sub-populations. In tokamak plasmas, long-wavelength modes interact with the second-adiabatic moment of EPs produced by neutral beams, external RF sources, or fusion-produced alphas. This leads to uncertainty in plasma stability boundaries and enhanced EP particle transport. EP closures based on the PIC algorithm have long been used in extended MHD codes to capture this important physics. The extended MHD code NIMROD has both continuum and delta-f PIC [1] drift kinetic (DK) capability. Serendipity shape functions, up to sixth order, have been implemented in the delta-f PIC DK approach in an attempt to provide more accurate integration of particle trajectories. Such an approach may be vital for accurate integration near the separatrix of a diverted tokamak and for preserving the second-adiabatic invariant. Careful comparison of the performance of the serendipity shape functions against the bilinear, reduced set that is often used in NIMROD PIC simulations, and the full 2D Lagrange polynomials is presented. Improvements in accuracy, efficiency, and memory gain when using the serendipity set are also presented. |
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JP11.00074: Overview of the instrumentation and control system for the IGNIS-2 surface science facility Carli S Smith, Matthew S Parsons, Jean Paul Allain, Hanna Schamis, Ethan Kunz The new IGNIS-2 in-situ surface science facility at Penn State will support innovative measurements of plasma-material interaction research, particularly focused on tungsten alloys, mixed-material surface chemistry, and liquid lithium films. IGNIS-2 will incorporate material characterization techniques such as X-ray Photoelectron Spectroscopy, Low-Energy Ion Scattering Spectrometry, Thermal Desorption Spectrometry, Raman Spectroscopy, and optical techniques to measure the chemical composition and morphology of materials during ion irradiation. The IGNIS-2 Instrumentation and Control (I&C) system will play a critical role in experimentation. Thus, we have dedicated effort to both the design and development of this system. I&C system software will help automate the experimental process by performing DAQ functions and running diagnostic tests on equipment as needed. The main functions of the I&C software will be to monitor pressure gauges, to actuate gate valves, vacuum pumps, and motors for sample manipulators, and to record experimental data in real time. The software will be written using the LabVIEW visual programming platform, which will display user-controllable panels that will communicate directly with the various IGNIS-2 components. In addition to software, a variety of commercial hardware components will be used to integrate the software with the individual sensors and actuators. The software and hardware will work together to provide an I&C system that will ensure the safety and reproducibility of our experiments. |
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JP11.00075: EDUCATION AND OUTREACH
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JP11.00076: Closing the equity gap in plasma science Royce W James, Arturo Dominguez, Carolyn C Kuranz, Elizabeth C Merritt, Nicholas Murphy, David E Newman, Edward E Thomas, Ellen G Zweibel APS DPP stands poised to create a healthy climate of diversity, equity and inclusion critical to solving the challenges we face in our field. We acknowledge, as a community, that lack of an open and welcoming climate is a serious problem and inhibitor to achieving our collective goals. Established institutional practices, tropes, and policies have caused and propagated harm to marginalized members and potential members of our honored division. In this presentation, we describe efforts by the DPP Diversity, Equity, and Inclusion Organizing Collective Committee (OCC) [1] over the last year to reduce equity gaps across the plasma community. The OCC is engaged in a three-pronged approach. First, we are developing a toolkit of evidence-based practices that are ready to be implemented by institutions in our community. Second, we are designing a queryable equity database of demographic and climate information for the DPP to evaluate and monitor equity gaps in the community, with strict safeguards to protect member privacy. Third, we are working towards a theory of practice that will jointly develop long-term community actions to eliminate equity gaps across the plasma community. |
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JP11.00077: Plasma open-source packages training for research activities via #2021PlasmaHackWeek Nicholas Murphy, Erik T Everson, Valentina Marascu, Stephanie Yang, Dominik Stanczak, David A Schaffner, Ramiz Qudsi, Steve Vincena, Sterling P Smith Plasma physics open-source software development training was carried out in a 5-days workshop from June 28th to July 2nd. We combined tutorials on various topics ranging from basic Python programming, PlasmaPy, Git & GitHub to specialized packages like OMFIT, BOUT++, SunPy, TurboPy, xarray. We also conducted multiple live "hacking" sessions. We define hacking as collaborative coding among novices, experts, and like-minded learners to work on projects, learn from each other and build the sense of computational plasma community. Hacking is a learn-by-doing activity, one of the best ways to further our knowledge. Moreover, open source software packages, for various applications in plasma and fusion physics, such as Aurora, divHretention, Tofu, OMAS, Gkeyll and BOUT++, were highlighted through either full sessions or lightning talks during the event. |
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JP11.00078: The ITER Thermonuclear Fusion Research-Education as the Vehicle in both National and Global Emergency Events, such as COVID-19 Pandemic V. Alexander Stefan It is argued that the ITER Thermonuclear Fusion Research-Education long-term project, in addition to its focus on the national-global energy emergency, can also facilitate the efforts in other emergency events, such as Covid-19 pandemic, via its scientific expertise; and also by its funding, equipment, personnel, etc. This would also augment the national-global stability. [1] [2] [3] [1] V. F. WEISSKOPF CENTER for NATIONAL-SECURITY-PHYSICS and GLOBAL COOPERATION-Stefan University; You Tube video: https://www.youtube.com/watch?v=aVtOYuX816s [2] V. Stefan (Editor-Author) Physics and Society (AIP-Springer, 1998)—In Honor of V.F. Weisskopf; p.21., Weisskopf, the Director General of the CERN. [3] M N Rosenbluth Summer School (S-U Press 2007 Marshall Nicholas Rosenbluth Center for Controlled Thermonuclear Fusion Studies-Stefan University; You Tube video: https://www.youtube.com/watch?v=0iCMIAX3tjA |
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JP11.00079: A Study on the Impact that the COVID-19 Pandemic had on STEM Learning in Elementary School Students Jorge Carmona Reyes, Augusto Carballido, Brenda Davis, Judy York, Kerry Brady, Truell W Hyde Last year STEM learning was impacted due to the COVID-19 pandemic when multiple schools had to provide instruction through virtual learning environments. Authors of this research developed a model to measure the impact the pandemic had on successful STEM learning [Carmona et al, 2020] using the concept of Student Engagement (i.e., effort, participation, autonomy, competence, sense of belonging, and personal relationships). This model correlates student engagement and academic performance to measure the manner in which the pandemic affected STEM learning. Early results show decreases in certain areas as expected; however, there are also unexpected results implying that some behaviors, perceptions, and constructs may have actually increased in other areas of the STEM learning process. In this presentation, we discuss how these results were obtained, how the variables of interest were measured, and the results and impact on STEM learning from multiple perspectives (i.e., teachers, students, independent observers). We will also discuss the impact the pandemic had on mathematics and science scores and student engagement and compare this to pre-pandemic levels. |
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JP11.00080: Methods and Effectiveness of Virtual Scientific Outreach at the DIII-D National Fusion Facility Elizabeth R Starling, Kathreen E Thome, Colin Chrystal, Richard L Lee, Cami S Collins Due to the sanitary restrictions imposed by the global outbreak of the COVID-19 pandemic, scientific outreach at the DIII-D National Fusion Facility has recently been limited to that which can be performed virtually. In this presentation, several examples of virtual scientific outreach are discussed, ranging from social media highlights of current research to virtual reality tours to interactive workshops which took place via Zoom, and the effectiveness of each method is explored. For social media, effectiveness is measured via the standard metrics of the number of views, likes, comments, and shares per post, as well as unique followers per account. For methods such as virtual tours and workshops, the potential for interactivity and/or follow-up communication is considered, as well as the satisfaction of the audience with the content presented, which is measured via follow-up surveys after each event. These measures of outreach effectiveness are compared with the amount of resources each method requires, including time, manpower, and financial requirements, and the potential for re-use of any materials developed for this purpose. |
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JP11.00081: Introducing PlasmaNOW: A Resource for Public Engagement and Education in Plasma and Fusion Shannon Greco, Eva Kostadinova, Amelia J Reilly Plasma Science and Fusion Energy public engagement serves to disseminate the research, build awareness and support, diversify the workforce, and allow scientists to learn about the concerns and interests of those outside their field. Here we propose to shift from a deficit model of "outreach," experts reaching out to novices, towards a model of mutual contribution and benefit enabled by a network, with the goal of building experiences based on research and robust evaluation. The recently published Community Plan for Fusion Energy and Discovery Plasma Sciences recommends that "we must increase pathways for undergraduates and technical workers, and increase science literacy by developing community outreach." To address this and similar recommendations, PlasmaNOW (Network for Outreach and Workforce) is a project that aims to build a network for public engagement and education practitioners ranging from scientists to educators and communicators. PlasmaNOW will provide a forum to share best practices, supporting research, and tools for Plasma Science and Fusion Energy engagement and education practitioners. It will also serve as a resource for teachers, students, and community members who wish to engage with these practitioners and the science. |
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JP11.00082: The Plasma and Fusion Undergraduate Research Opportunities (PFURO) Program Arturo Dominguez, Steffi J Diem, Deedee Ortiz, Andrew P Zwicker The recent APS-DPP Community Planning Process (CPP), as well as the FESAC Long Range Plan (LRP), highlighted the need for a robust and diverse workforce to tackle the challenges of a growing plasma physics and fusion energy field. One specific recommendation from the CPP (recommendation B-6) was the creation of a summer research program for undergraduate students. Within the workforce development section of the LRP report, it recommends to “Reinstate and create fellowships to help recruit and retain top students from – a diverse applicant pool into FES research areas.“ |
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JP11.00083: Strategic Fusion Energy Communications on the Road Towards a US Fusion Pilot Plant Andrew P Zwicker With the release of the Community Planning Process and FESAC reports, as well as the National Academies studies, our community has reached a key moment in the development of fusion energy. Additionally, significant investments have been made in the private sector to accelerate the production of a fusion pilot plant. A key need moving forward is the development of a strategic communications plan that captures these recent developments and targets key stakeholders at both the national and local levels. In response, a group of communicators from national labs, universities, and the private sector have formed a coalition called the Council for Fusion Communications (CFC) to assist in the ongoing efforts within the fusion energy community. An overview of CFC and plans for next steps will be presented. |
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JP11.00084: A closer look: Remote internships during COVID-19 times Deedee Ortiz, Arturo Dominguez, Andrew P Zwicker, Shannon Greco
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JP11.00085: HIGH SCHOOL RESEARCH
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JP11.00086: Likelihood-free inference using normalizing flows for experiment and simulation comparison Chirag Furia, Michael Churchill Modeling the scrape-off layer (SOL) in a tokamak device requires multi-physics processes such as turbulence, neutral transport, and material interactions. Ad-hoc anomalous transport coefficients are often employed in fluid code modeling, as turbulence is difficult to simulate, but require tweaking by hand in plasma codes to match observations. We introduce likelihood-free inference with normalizing flows to automate this process, determining the statistical significance of input parameters to match given observations and possibly revealing alternate parameter configurations that may otherwise be overlooked. Likelihood-free inference uses machine learning to approximate the posterior function p(θ|x) of a simulation’s input parameters, θ, given a set of outputs, x. Normalizing flows, which are constructed by neural networks and enable the mapping of a simple distribution to a far more complex one, are chosen to represent this desired distribution. The UEDGE 2D fluid simulation code is used to generate steady-state outer midplane and divertor measurements for a configuration given an input dataset of anomalous transport coefficients. The dataset is then used to train the normalizing flows, which are assessed using log probabilities. |
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JP11.00087: Machine Learning enabled detection of ELM-Precursors in KSTAR ECEI data. Cooper H Jacobus, Ralph Kube, Minjun J Choi The emergence and dynamics of edge-localized filamentary structures inside tokamaks during high-confinement mode can be studied using an ECEI (Electron Cyclotron Emission Imaging) diagnostic system. This diagnostic samples a temperature map of a 2D poloidal cross-section of the plasma on a microsecond time scale. Previously, detailed analysis of these filamentary dynamics and classification of the precursors to edge-localized crashes has been done manually. We present an algorithmic approach capable of automatically identifying the position and dimension of these filaments. This is achieved using a Single-Shot Detection convolutional neural network (SSD), a type of machine learning algorithm that detects features within images and proposes specific regions in which it expects a certain object is present. The machine learning model has been trained and optimized on an extensive set of manually labeled ECEI data from KSTAR (Korean Superconducting Tokamak Advanced Research), allowing the model to "learn" the features that constitute a precursory filament. In order to be even more hands-free, the algorithm is also capable of filtering raw ECEI data and masking out bad channels automatically; reasonably inferring masked data based upon neighboring channels. This model will allow for a more efficient and broad study of edge-localized filamentary dynamics with the aim of achieving a better understanding of edge localized mode crashes. |
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JP11.00088: Extraordinary and Z-Mode wave propagation in the auroral electron density cavity Andrew Ji, Eun-Hwa Kim, James W LaBelle Numerous satellites observed the electron density cavity in which the electron plasma frequency (fpe) is much less than the cyclotron frequency (fce) in the auroral region. The density cavity is known as a source region of auroral kilometric radiation (AKR) since the low densities favor wave growth in the extraordinary wave mode. The AKR is generated by the electron cyclotron-maser instability, which excites extraordinary (X) modes, ordinary (O) modes, and Z-modes. Therefore, understanding wave properties near the density cavity is critical to understand AKR propagation characteristics. This presentation demonstrates the plasma wave dispersion relation near the auroral electron density cavity and boundaries by adopting an empirical ionospheric density model such as the international reference ionosphere (IRI) with a density depletion effect. Because the dispersion relation of X- and Z-mode dramatically changes along with fpe/fce; thus, we mainly focus on X- and Z mode wave propagation near the boundaries. The results provide the cutoff and resonance condition of each wave mode and predict wave properties detected spacecraft observations when waves traverse through such cavity boundaries. |
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JP11.00089: Lower Hybrid Drift Waves during Magnetic Reconnection in Earth's Magnetotail Rohan R Kulkarni, Erik Ji, Hantao Ji, Narges Ahmadi, Kendra A Bergstedt Understanding the dissipation mechanisms required for fast magnetic reconnection is critical to predict space weather phenomena such as solar flares to take preventative measures for protecting spacecraft and communication systems. Plasma waves in the lower hybrid frequency range have already been observed in the Magnetic Reconnection Experiment (MRX) and are a candidate dissipation source. In this research, we process and analyze spacecraft data from the Magnetospheric Multiscale (MMS) Mission to highlight the occurrence of various plasma waves during reconnection in Earth's magnetotail. First, we build a data processing platform based on Jupyter Lab to download data in CDF format from various MMS spacecraft and process it in Python. We then use our Python modules and frameworks to visualize the data. Next, we validate the efficacy of our data processing tools against previously documented data. Finally, we utilize our tools to analyze datasets from recent magnetic reconnection events and compare them with theoretical predictions. The results could characterize the propagation of lower hybrid drift waves and other electromagnetic fluctuations, as well as provide new insights on the timing and magnitude of energy dissipation during fast reconnection. |
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JP11.00090: Jupyter Notebook for Analyzing and Visualizing Stellarator Properties Santiago Lisa, Nastassia Patnaik, Nathaniel Stauffer, Tony Qian, Chesson S. Sipling, Brian X Jiang, Wenxi Wu, Sreya Vangara, Sorah Fischer, Bharat K Medasani, William D Dorland, Michael C Zarnstorff The application presented is a Jupyter notebook that allows users to analyze properties of inputted stellarator configurations. Data can be provided manually, through a .txt file, or through an existing configuration entered into the Fuse0D spreadsheet. The Python script calculates optimized helium concentration, volume averaged density, and Pheat estimates according to the model proposed in Hammett et al (2019). Using these generated values, a Q value for the stellarator configuration is maximized and the ISS-04 H confinement scaling multiplier is minimized. The user may iterate one or two parameters over a given range to visualize the effect of changing configurations in a two-dimensional or three-dimensional graph—this functionality would be displayed on a laptop at the conference. The application is designed to allow easy and accurate analysis of stellarator properties, allowing users to identify promising configurations and eliminate those with poor performance. |
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JP11.00091: Python Application to Evaluate Stellarator Performance nastassia patnaik, William D Dorland, Michael C Zarnstorff, Tony Qian, Santiago Lisa, Nathaniel Stauffer, Wenxi Wu, Chesson Sipling, Braden Buck, Sorah Fischer, Brian X Jiang, Dominic Seidita The goal of this project is to create an interactive Python application to analyze and create visual representations of the performance of potential stellarator configurations. We use 0D scaling formulas used by Hammett et al. (2019), but the application is adaptable to more complex formulations. Our code provides a tool to explore the impact of changes in various parameters on stellarator efficiency. Our code generates optimized heating power estimate, volume averaged density, and helium concentration estimate values, which are then used to calculate a maximized fusion Q, and a minimized ISS-04 confinement multiplier within the design constraints of the proposed stellarator configuration. This tool is best used as a method to quickly and accurately identify and focus on attractive stellarator geometries. |
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JP11.00092: Monitoring Space Weather from the ISS Using Space PlasmA Diagnostic SuitE (SPADE) Data Amrita Sahu, William E Amatucci, Ami M DuBois Modern society is highly dependent on satellite-based information and communications systems. Similar to the effects that major storms have on daily life, extreme space weather can harm satellite operations and high-voltage terrestrial power grids. Consequently, monitoring space weather is essential and requires its own set of diagnostic tools. SPADE is one such tool developed by NRL to characterize the low Earth orbit plasma environment from aboard the ISS. For example, the SPADE impedance probe finds plasma density by identifying natural resonances that are dependent on the local magnetic field. Thus, effective use of the impedance probe requires an accurate magnetometer measurement. The SPADE magnetometer data was calibrated with the International Geomagnetic Reference Field (IGRF-13) model and used to interpret impedance probe measurements along the ISS orbit. Plasma density and other parameters are also affected by geomagnetic activity, making SPADE a promising instrument for identifying space weather. While analyzing deviations between SPADE’s magnetic field measurements and the IGRF-13 model, we looked for correlations between impedance probe data and geomagnetic activity. The calibrated SPADE data could provide valuable information to help develop space weather models. |
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JP11.00093: UNDERGRADUATE RESEARCH
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JP11.00094: Python Platform as a Basis for RF and Spectral CubeSat Data Collection Christian Coronel, Royce W James, Jennifer Boughton, Brian Kay, Richard W Freeman, Lorraine A Allen Together the U.S. Coast Guard Academy, Naval Research Lab, U.S. Naval Academy, Old Dominion University, and the Air Force Institute of Technology have built upon the technology in the ‘Space PlasmA Diagnostic suitE’ (SPADE) mission operating from NASA’s International Space Station to construct a 3U CubeSat with multiple payloads. The AC impedance measurements are collected as raw data using a sweeping frequency through surface-mounted antennas. While the compact multispectral ‘Pixel Sensor’ with a 450 nm - 1000 nm spectral range plus the motion and position sensor data are bundled and transmitted through the CubeSat bus. Original python code, which will serve as a hub to unify the existing MATLAB and LabVIEW code, and provide near-time results during the short-lived mission. Data parameters, and laboratory density comparisons to previous experimental analyses will be reported. |
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JP11.00095: Application of the Permutation Entropy and Statistical Complexity AnalYsis (PESCy) Technique to the Dust Acoustic Wave Julianna Schoenwald, Jeremiah D Williams, David A Schaffner A dusty plasma is a traditional plasma system with a third charged species consisting of nanometer to micron sized particulate matter. The presence of this third charged species results in a system that is notably more complex than the traditional plasma system and supports a wide range of physical phenomena, including a low-frequency longitudinal wave mode known as the dust acoustic wave. Measurements of this wave mode have suggested that turbulence can be observed under the appropriate experimental conditions. To gain a deeper insight into the behaviors of dust acoustic waves, we will be employing the Permutation Entropy and Statistical Complexity AnalYsis (PESCy) technique. In this technique, the Permutation Entropy and Statistical Complexity quantities characterize the complexity of a given signal and classify it as either periodic, noisy, or chaotic. In our presentation, we will compare the results of our PESCy analysis to a Fourier analysis and discuss how the PESCy technique can be used to quantify dust acoustic wave phenomena. |
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JP11.00096: Effective atomic number diagnostics for plasma instabilities using Talbot-Lau X-ray Moire Deflectometry Victor Flores, Maria Pia Valdivia Leiva, Gabriel Perez Callejo The Talbot-Lau X-ray Moire Deflectometer (TXD) is a single image phase-retrieval plasma diagnostic. TXD can simultaneously provide x-ray attenuation, refraction, elemental |
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JP11.00097: Two dimensional density reconstruction via inversion of interferometer and soft x-ray data in the Wisconsin HTS Axisymmetric Mirror (WHAM) Michael Johnson, Jay K Anderson, William J Capecchi, Douglass A Endrizzi, Cary B Forest, Jonathan D Pizzo, Kunal Sanwalka A new axisymmetric magnetic mirror (WHAM) is currently under construction at the University of Wisconsin. Essential amongst the first measurements is determination of the electron density profile. In conjunction with design of a multi-chord interferometer, a modified Abel inversion technique is developed for fitting experimental data. A four free-parameter fit is performed on an anticipated six chord measurement of line-integrated density. Refinement of the reconstructed density profile is then conducted by analysis of soft x-ray emissivity measured on a multi-chord pinhole camera geometry. Synthetic signals from the CQL3D code are used to optimize diagnostic geometry and sensitive energy range prior to implementation. While the interferometer will measure density at the center of the device, accumulation of sloshing fast ions at higher magnetic field positions will lead to variation of density along the axial direction. Full orbit studies of the fast ion population are utilized to predict the density enhancement and help inform the RF/fast ion resonant interaction. |
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JP11.00098: Investigation of Lost-alpha Power due to Neoclassical Tearing Modes in the SPARC Tokamak Anson Braun, Gerrit J Kramer, Roy A Tinguely, Steven D Scott Using the SPIRAL Monte Carlo, full particle-orbit simulation code [Kramer PPCF 2013], we investigate the effects of neoclassical tearing modes (NTMs) on power loss in the SPARC primary reference discharge [Creely JPP 2020, Rodriguez-Fernandez JPP 2020]. We predict increased alpha-power loss in the SPARC design due to NTMs synergizing with toroidal field ripple and orbital losses. Transport through the stochastic regions associated with the 2/1 and 3/2 NTMs, located at ρpol≈0.86 and ρpol≈0.76 respectively, are expected to increase particle flux into the lossy region of the plasma (ρpol>0.8). Alpha particles born in the lossy region are predicted to contribute to 95% of the total lost-alpha power in the SPARC tokamak [Scott JPP 2020], so increased particle flux into this region will increase power loss, leading to lower plasma performance. We investigate this prediction using the SPIRAL code to follow ensembles of particle paths through a simulated SPARC magnetic equilibrium perturbed by NTMs of widths up to a geometric limit. |
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JP11.00099: Image Analysis for Porosity Measurements of Early Fine-Grained Rim Analogs Izzy Thomas, Graeson Griffin, Jorge Martinez Ortiz, Truell W Hyde, Lorin S Matthews, Augusto Carballido, Abbie Terrell Chondrites are meteorites that contain large, round mineral grain deposits called chondrules. As remnants of the early solar system, chondrites offer abundant knowledge about the plasma environments around young stars. However, the precise cause of their formation remains unknown. Fine-grained rims (FGRs), the layers of compacted dust surrounding chondrules, are particularly insightful for investigating the protoplanetary disk dynamics that lead to planet formation. This study examines the early stages of FGR formation by using an experimental analog for the accretion of dust onto a chondrule surface by depositing dust grains onto a surface within a vacuum. Slices of the dust pile are obtained through laser sheet scanning techniques. Image analysis methods are used to obtain experimental porosity measurements of the dust piles. Successive images are binarized and subtracted to reveal changes in the dust pile's morphology. However, this leaves the dust pile hollow. This poster presents image processing techniques used to digitally fill the dust pile center to determine structural porosity and discuss the use of these dust pile contours to calculate surface porosity. |
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JP11.00100: Petra-M Full Wave Simulation of Parasitic Coupling to the Slow-Wave During ICRF Experiments on LAPD Sophie Wood, Gurleen Bal, Syun'ichi Shiraiwa, Bart V Compernolle, Troy A Carter A 3D full wave code, Petra-m1, was used to simulate wave propagation from a single strap RF antenna in the Large Plasma Device (LAPD). Petra-M simulations allow for importing 3D CAD models of the RF antenna used in the experiments as well as experimentally measured density profiles. The experiments were carried out in a magnetized helium plasma with plasma parameters ne ~ 1018 – 1019 m-3, Te ~ 1 – 10 eV and B0 ~ 0.1 to 0.18 T. This work will compare experimental data to simulation results of the short wavelength, slow wave propagation in the plasma edge, low density region. Experiments were performed at 5-15 MHz with evidence of coupling fast-wave in the core and slow-wave in the edge were observed. With an improved solver and access to finer mesh elements, we are able to resolve the slow wave edge dynamics. Validating the simulated edge interaction with experimental results plays an important role in helping us understand interactions between RF waves and the SOL region of fusion devices. |
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JP11.00101: SAPO family as greenhouse gas plasma assisted capture system for atmospheric remediation Jaimiely Garcia Cajiao, Maria Carreon The direct capture of CO2 and CH4 from the atmosphere to stabilize their concentration in the air to control global warming is accelerating. There are continued efforts to develop and optimize different technologies for direct capture of these greenhouse gases from air. In this work we employed a SAPO zeolite family as efficient and robust CO2 and CH4 adsorbents at standard temperature and pressure conditions. Herein, we demonstrated the possibility of employing nonthermal plasma to desorb and react these greenhouse gases. The desorption of the gases under study were performed when employing gentle plasma pulses of Kr. Interestingly, the desorption of CO2 and CH4 occurred when the plasma was turned off, which is opposite to the case of other small pore size materials studied by our group, such as MOF-177. Suggesting a kinetically limiting process rather than a thermodynamically dominated phenomenon. The zeolite SAPO-56 resulted in a maximum CH4 desorbed molar flow rate of 23.27 µmol min-1 when applying a plasma disturbance. While for CO2 the maximum desorbed molar flow rate was 28.43 µmol min-1 . When reacting CH4 and CO2 under plasma environment for the specific case of SAPO-56 at (5:1) (CH4: O2) flow ratio, we observed the highest CH4 and CO2 conversions of 10.39% and 11.12% respectively. We concluded that this type of acidic catalyst resulted in a higher production of CO compared to the methanol formation. We expect this preliminary understanding of the adsorptionreaction system under non-thermal plasma environment can lead to future atmospheric remediation technologies. |
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JP11.00102: Localizing Alfvén eigenmodes in plasma based on high resolution ECE spectrograms at DIII-D using autoencoders and image processing techniques Eric Ahn, Azarakhsh Jalalvand, Egemen Kolemen Despite the promising achievements in fusion production, tokamaks still suffer from kinetic and MHD instabilities. In this work, we focus on Alfvén eigenmodes (AEs), a class of ubiquitous mixed kinetic and MHD instabilities, and present a data-driven pipeline to efficiently locate them in ECE spectrograms. ECE spectrograms have naturally high levels of noise, which must be reduced before further processing. For example, the classification and localizing rate of the AEs on raw spectrograms is about 60%. State-of-the-art deep learning techniques for enhancing the images need to see both noisy and clean versions of the data during the training which is something unavailable to us. To alleviate this issue, we first employ a pipeline of existing image processing techniques to partially denoise the spectrogram. These techniques, which include Gaussian filtering, median filtering, and morphological filtering, provide a baseline denoised image. The output of this pipeline is then used as a target for autoencoders to further enhance and segment the spectrograms using deep learning and autoencoder algorithms for localizing the AE instabilities. |
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JP11.00103: The pulse-pile-up tail artifact in pulse-height spectra Taosif Ahsan, Charles Swanson, Tony Qian, Tal Rubin, Samuel A Cohen Pulse pile-up in pulse-height energy analyzers increases when the incident rate of pulses is comparable to or larger than the pulse pair resolving time of the detection system. Large changes in the observed energy distributions with incident rate and pulse shape then occur. In this paper we focus on the high energy tail of X-ray spectra, important for measurements on partially ionized, warm, pure-hydrogen plasma. A two-photon pulse-pile-up model is derived for trapezoidal-shaped pulses produced in Amptek Fast SDD detectors and quantitative agreement is found between the measurements and the model predictions. Further progress was made to extend the model to an arbitrary number of photon PPU by making use of Fourier transform on convolution terms which enabled the model to handle spectrum with arbitrary total count rate. |
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JP11.00104: Analyzing Proton Radiographs for Magnetized HED Plasma Experiments with an In-Situ X-ray Reference Rafia Alamgir Developing precise methods for the measurement of magnetic fields is an important tool for understanding the interactions of magnetic fields and magnetized high energy density (HED) plasmas relevant to laboratory astrophysics and magnetized fusion schemes. We report a novel technique of proton radiography that was developed and implemented to precisely measure non-uniform magnetic fields in HED plasma at the Omega laser facility. A DHe3 capsule is used to produce both protons and intense x-rays. By placing a mesh grid between the capsule and plasma, the proton beam is split into smaller beamlets, which are deflected by the plasma's electromagnetic fields to a detector stack. The detector stack consists of two CR39 plates for measuring deflections of 3 and 15 MeV protons and an X-ray image plate for an absolute reference of undeflected beamlets. In this work, automated algorithms for calculating beamlet deflections are developed to construct a 2D map of magnetic fields. This analysis is applied to HEDP experiments for plasmas expanding into a background magnetic field and magnetic reconnection experiments of two colliding plasmas. |
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JP11.00105: Bounce-Averaged Fokker-Planck Solver based on the MFEM Finite Element Library Benjamin R Antognetti, Syun'ichi Shiraiwa, Nicola Bertelli The required toroidal currents for magnetic confinement in tokamaks can be driven by radio frequency (RF) waves. The resulting changes in the electron velocity distribution function are modeled by the Fokker-Planck (FP) equation. In the past, we built a FP solver based on the MFEM (www.mfem.org) finite element method library to take advantage of a modern GPU computing architecture the results of which were presented at the APS DPP 2020 Annual Meeting (JP13.00021). This initial work solved the FP equation for the steady-state distribution function of a uniform plasma with external RF-induced quasi-linear diffusion. In order to apply it for toroidal devices, we extended our solver to include bounce averaging, relativistic effects, and temporal evolution. The simulation results of this solver are compared with a reference simulation computed using CQL3D. |
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JP11.00106: Analysis of Liquid Lithium as a Plasma Facing Component using LAMMPS Code Stephen Armstrong, Sierra E Jubin, Igor Kaganovich This research will analyze the interactions between a small amount of liquid lithium and hydrogen species impinging upon it using a full molecular-dynamics code LAMMPS. Previous research in this area has used coupled Monte-Carlo simulations and two-dimensional REDEP/WBC codes primarily for attempting to model full reactor scale interactions between a solid lithium wall (Ruzic, David N. 2003). Other research has used TRIM (Transport of Ions in Matter), a binary collision approximation, derivatives to determine the retention coefficients and sputtering yields of D+ species on solid lithium (Qiu, Hua-Tan 2005). In addition, research as covered the surface chemistry of lithiated carbon PFCs (Kristic, P.S. 2018). This current research will look at sputtering and retention of hydrogen in lithium at smaller time scales, various plasma conditions. The LAMMPS molecular dynamics simulation will be used to model small scale interactions between the liquid lithium and H+, or D+ ions. LAMMPS is able to simulate small length and time scale interactions allowing a detailed analysis of the interactions between the liquid lithium plasma facing components and the plasma ions. |
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JP11.00107: Machine learning autoencoder models for compressing and reconstructing 2D BES data for real-time classification tasks. Prannav Arora, Lakshya Malhotra, George McKee, David R Smith, Zheng Yan, Mark D Boyer, Ryan Coffee, Azarakhsh Jalalvand, Egemen Kolemen Multi-channel fluctuation diagnostics capture the plasma dynamics. Here, we report on an effort to develop machine learning (ML) models for the real-time identification of edge-localized-mode (ELM) events and the turbulence properties of confinement regimes using the 2D Beam Emission Spectroscopy (BES) system at DIII-D. The "edge ML" models will be deployed on a high-throughput FPGA accelerator for integration in the real-time plasma control system (PCS). The models will generate reduced signals that correspond to ELM activity and turbulence dynamics, and the real-time PCS will be trained to avoid ELM regimes and to maintain advanced confinement regimes such as the wide pedestal QH-mode. The 2D BES system captures density perturbations imprinted in neutral beam emission at a 1 MHz frame rate. Here, we report on autoencoder neural networks to compress the spatial-temporal information in a low-dimension space. Using such an autoencoder, we plan to compress BES data for ELM classification and other classification tasks. Currently, we experiment with the number of hidden layers and network architecture to maximize the capability of the network to compress and reconstruct 2D BES data as measured by a mean squared error loss function. |
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JP11.00108: Monte Carlo Studies of Bremsstrahlung Emissions for HEDP and Ignition Radiography Sarah N Azhar, Dean R Rusby, Adeola C Aghedo, Nuno Lemos, Shaun M Kerr, Jackson Williams, Andrew J Mackinnon X-ray radiography is used for studying high energy density and ignition experiments. MeV x-rays generated via Bremsstrahlung emission during short-pulse high-intensity laser experiments are ideal for high resolution radiographs. This is due to their small source size (100 µms), short pulse (1-10 ps), and high energy. This work builds upon the investigation of laser driven radiography conducted at the Titan, Omega EP, and NIF ARC facilities. Presented here are two GEANT4 studies to model the x-ray source in order to improve radiography capabilities. A database of x-ray outputs was created using GEANT4 simulations of monoenergetic electrons incident to high-Z foils of varying thicknesses. This database estimates the x-ray number and output energy of any desired electron input, enabling us to better understand the experimental x-ray data and optimize future experiments. The second model draws from GEANT4 simulations with varying initial electron sources and analyzes discrepancies in the resulting source size and emission angle of the x-rays. The resolution of the x-ray radiograph can be found by analyzing the curved-knife edge-spread function from the simulations. This allows us to optimize the source size and emission angles of the electrons for the highest resolution radiographs. |
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JP11.00109: Simulations validating the ponderomotive filamentation figure of merit Lucas Babati, William A Farmer, Mikhail Belyaev, Richard L Berger, Thomas D Chapman, Denise E Hinkel, Edward A Williams The pondermotive force due to a laser propagating through a plasma creates density wells, resulting in a spatially varying index of refraction and causing the laser to self-focus. If the intensity of the laser is sufficiently high, the laser will spray due to the self-focusing of each speckle within the beam profile. This process can result in degraded coupling to targets used in laser-driven experiments. Here, we examine the filamentation figure of merit (FFOM) that estimates the threshold at which the laser will self-focus. Two metrics are developed to assess the degree to which self-focusing is occurring: one associated with the angular dispersion of the beam and the second with the fraction of beam power over five times the average intensity. pF3D simulations of a speckled laser beam generated by a random-phase-plate (RPP) in a background plasma are reported, and the two metrics are determined from the simulations. It is shown that these metrics can diagnose self-focusing and that the predicted thresholds agree with the FFOM. These simulations are then used to assess filamentation of the beam and are extended to include polarization smoothing (PS) and smoothing by spectral dispersion (SSD). |
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JP11.00110: Control system for the HADES Pulsed Power Driver and Diagnostics Aidan Bachmann, Andrew Balogh, Eric Elias, Zihao Lin, Pierre-Alexandre Gourdain The High Amperage Driver for Extreme States (HADES) at the University of Rochester is a pulsed power driver which utilizes Linear Transformer Driver technology for the study of plasmas and warm dense matter in a laboratory setting. HADES requires a robust control system in order to oversee the machine's status; monitor switch triggering; coordinate diagnostic timing; and maintain ancillary systems such as oil circulation and vacuum. To achieve this end, we use 22-bit pulse generators to provide delays on the nanosecond scale, Pulse Width Modulators (PWMs) to control charging voltage, and Analog-to-Digital Convertors (ADCs) to monitor capacitor voltage. In addition, we use fiber optics to send and receive information to reduce the signal to noise ratio for all monitored systems. We will give an overview of each of the different control systems utilized, as well as discuss the design and implementation process. We extend this design to the system controlling a Thomson scattering diagnostic. |
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JP11.00111: Modeling powder injection experiments in LHD with the DIS and DUSTT codes RAHUL BANKA, Federico Nespoli, Mamoru Shoji, Kawamura Gakushi Recent boron powder injection experiments performed on the Large Helical Device (LHD) have shown beneficial effects on plasma performance through real-time wall conditioning [1, 2]. Several diagnostic measurements and modeling with EMC3-EIRENE and DUSTT codes suggest deeper penetration of B powder grains into low-density plasmas, making them a better candidate for boronization applications [3,4]. Correct modeling of the dust trajectory is fundamental for the correct interpretation of this kind of experiment. To this end, the Dust Injection Simulation (DIS) was recently developed, with the capability of handling 3D, time-varying plasma backgrounds [5]. To determine the dust grain trajectory, DIS solves Newton's equation, along with the equations for dust electric charge, temperature, and evaporation rate. Here we present the comparison of results gained from DIS and from the more established DUSTT code [6], using EMC3-EIRENE [7,8] simulations from the LHD serving as the 3D plasma background. Preliminary results show a qualitative agreement between the two codes. |
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JP11.00112: Wave absorption measurements of the electron distribution in the Space Physics Simulation Chamber Jonathan Barrett, Jim Schroeder, Erik M Tejero, Fred N Skiff High resolution measurements of electron distributions in laboratory plasmas can give needed insight into fundamental questions of plasma behavior. For example, upcoming experiments in NRL's Space Physics Simulation Chamber (SPSC) will investigate the kinetic plasma physics of chirped whistler-mode chorus emissions and wave-particle interactions that are predicted to play a significant role in the dynamics of Earth's radiation belts. Preliminary SPSC experiments investigate two diagnostic techniques: electrostatic energy analyzers and wave absorption. Because whistler-mode waves are absorbed by Doppler-shifted cyclotron resonant electrons and the amount of absorption is related to the number of resonant electrons, wave absorption uses low-amplitude whistler-mode waves to measure parallel electron velocity distributions. In our analysis of preliminary data, we relax the assumption that the background velocity distribution is Maxwellian so that we can use wave absorption in both equilibrium and non-equilibrium plasmas. Additionally, the interference produced by multiple simultaneously propagating probe wave modes is mitigated using Fourier analysis. In ongoing experiments, we are bench-marking energy analyzer and wave absorption techniques and exploring radiation-belt physics in the SPSC. |
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JP11.00113: PIC-simulation of ultra-intense laser plasma interaction with silica microspheres Hayden Beatty, Enam Chowdhury, Joseph R Smith Mass limited targets (MLT) in laser plasma interaction (LPI) is a reliable pathway to achieving warm and hot dense matter (WDM/HDM) states. The effects of ultra-high intensity laser light on various geometric arrangements of silica microspheres as MLT were investigated using 2D and 3D EPOCH particle-in-cell code. Multiple target configurations were used with one, two, and three 1 µm diameter silica sphere(s), where the laser, with 1020 W/cm2 peak intensity, 400 nm wavelength, 40 fs pulse duration and a 1 µm beam waist radius, is focused onto a single sphere. Initial conditions were charge-neutral and room temperature (300 K), with both Si and O atoms set to field ionize using a semi-classical tunneling ionization model, and releasing electrons in strong accelerating fields. All simulations were carried out up to 1000 fs. Comparison of single vs multiple sphere cases show that the spheres not directly hit by the laser exhibit different charged particle dynamics. The results showed all particle species ejected from the rear in distinct geometric patterns (“jets”) several hundred fs after laser impact in the three-sphere configuration where the laser is focused onto the middle sphere only. Ionization of adjacent spheres with minimal dispersion is also demonstrated. |
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JP11.00114: Modeling Spatially Resolved Neutral Atom Densities in the PFRC-2 Using DEGAS 2 Catherine Biava, Samuel A Cohen, George J Wilkie, Arthur Dogariu Krypton and atomic hydrogen densities have been measured in the PFRC-2 plasmas using a two-photon-absorption laser-induced-fluorescence (TALIF) diagnostic. Because of their disparate energies and masses, these two fill gases provide a range of ionization mean-free-paths, L, from (L/plasma radius) below 0.01 to above 10. The first condition is comparable to that in tokamaks, allowing smaller experiments to explore the effects of neutrals in larger denser plasma devices. Upon plasma initiation in the PFRC-2, the gas is partially ionized and the densities of the atomic H and Kr in the plasma increase from 0 to 10e11/cc and decrease from 2e13 to less than 2e12/cc respectively. We use the DEGAS 2 code to compare with the experimental results, testing, for example, the roles of wall collisions and molecular processes on neutral behavior. |
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JP11.00115: Simulation of diamond growth using LAMMPS Jessica Bookholdt, Sierra Jubin, Igor Kaganovich The intention of this research is to use the LAMMPS molecular dynamics code to simulate the initialization of nanodiamonds and their growth. |
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JP11.00116: Optimization of Energetic Particle Confinement in the W7-X Stellarator Dalton Branson, Andrew S Ware Computational modeling is used to calculate the expected bootstrap current in the Wendelstein 7-X stellarator (W7-X) and determine the impact of this current on the confinement of energetic particles. The confinement of 60 keV ions in W7-X has previously been examined for the base W7-X configuration [M. Drevlak, J. Geiger, P. Helander and Y. Turkin, Nucl. Fusion 54, 073002 (2014)]. In this work, comparison of the base and a mirror W7-X configuration are analyzed, including the effects of increasing β and self-consistent bootstrap current. The confinement of energetic ions is analyzed as well with varying current in the planar coils. A long term goal of this work is to search for configurations with improved energetic particle confinement using stellarator optimization tools. |
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JP11.00117: Nonlinear Propagation of High-Intensity Light Through Plasma Volume Diffraction Gratings James G Brutus, Pierre A Michel, Matthew R Edwards Transmission gratings diffract incident light at specific angles and allow wavelength-specific manipulation of laser pulses. We simulate the performance of plasma transmission gratings that are based on the refractive index difference between ionized and non-ionized gases. The gratings are driven by the interference of two high energy femtosecond pump beams and characterized with a delayed probe beam. The diffraction efficiency of the plasma grating structure is measured under varied pump and probe divergence, wavelength, angle of incidence, and energy. We determine the effective damage threshold of the gratings by characterizing the decrease of diffraction efficiency for increased probe beam power, allowing us to understand the performance and ultimate limits of plasma-based high-power laser systems. |
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JP11.00118: A coding pipeline to quickly analyze turbulence for stellarator optimization Braden Buck, Chesson Sipling, Brian X Jiang, William D Dorland, Michael C Zarnstorff, Tony Qian, Sorah Fischer, Michael Cole, Nastassia Patnaik, Santiago Lisa, Nathaniel Stauffer, Wenxi Xu Turbulence within a stellarator can lead to significant core heat loss and low temperature profiles that are not conducive to achieving fusion. As such, the plasma dynamics and stability need to be carefully considered when designing an optimal plasma configuration. We are constructing a framework of code that will accurately and quickly yield predictions of plasma turbulence given a magnetic field configuration of a stellarator. This framework will be a three-step pipeline of code consisting of a magnetohydrodynamic equilibria solver (VMEC), a magnetic coordinate transformation code (GIST and FIGG), and a gyrokinetic solver (GS2). Emphasis is placed on calculating the critical temperature gradient for the ion-temperature-gradient (ITG) mode of microinstability for a series of stellarators based on the results from GS2. The ITG mode is used because of its significant role in turbulent transport in stellarators. Once this pipeline is constructed and optimized, it can be connected to an algorithm that generates stellarator designs to find the ones that would potentially yield the least amount of turbulence. |
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JP11.00119: Implementing particle and ray-based algorithms in heterogeneous environments for plasma simulations Matthew Burns, Sreepathi Pai, Adam B Sefkow, Russell K Follett The proliferation of CPU-GPU heterogeneous comput- |
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JP11.00120: Taylor State Merging Studies: Experiment Kya M Butterfield '24, Michael R Brown We present the results of a series of experiments that investigate the dynamical merging of large aspect-ratio plasmas in the Swarthmore Spheromak Experiment (SSX) device. In SSX, two plasmas evolve and collide within a copper flux conserver with an aspect ratio of $\ell/R \cong 10$. Plasmas twist into relaxed Taylor states, with typical velocity $40~km/s$ , density $n_e = 0.5 \times 10^{16}~cm^{-3}$, proton temperature $T_i \approx 20~eV$, and magnetic field $B \approx 0.4~T$. As the plasmas collide, measurements of interest are line-averaged plasma density, fluid-scale vector B-field (distance between probes $\sim 32~\rho_i$, and plasma temperature, acquired via Helium-Neon interferometry, a 2D $4\times4$ grid array of B-dot probes, and Ion-Doppler Spectroscopy (IDS) respectively. We compare measured data to Dedalus-framework simulations (see S. Yang et al this session). We merge Taylor State configurations of both co- and counter-helicity (either with the same or opposite directions of twist). We observe appreciable ion heating, consistent with magnetic reconnection. Finally, we discuss the suitability of merged Taylor states for use as Magneto-Inertial Fusion (MIF) targets. |
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JP11.00121: Taylor State Merging Studies: Simulation Shouzhuo Yang, Michael R Brown We present the results of a resistive Magnetohydrodynamic (MHD) simulation of the evolution and merging of two Taylor state plasmas. We write our simulation program in the Dedalus framework, a module that solves differential equations with spectral methods (http://dedalus-project.org/). The computation is performed with the Pittsburgh Supercomputer Center. The simulation models merging experiments at the Swarthmore Spheromak Experiment (SSX), where we have characterized the magnetic structure, velocity (40 km/s), density (0.5x1016cm-3), proton temperature(20 eV), and magnetic field (0.4 T) of relaxed helical Taylor states. We compare data generated through the simulation and the experimental data collected at SSX using 16 Langmuir probes (see K. Butterfield et al. this session). Quantities of interest are the line averaged plasma density, vector B-field, and plasma temperature. |
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JP11.00122: Efficiency and Modularity of ALFVN (Adaptive Lightweight Finite Volume Numerics) Hydrodynamics Code Rachel Wang, Siddhant Solanki ALFVN is a versatile 3D hydrodynamics Python code which solves conservative equations of hydrodynamics using finite volume methods. It's written to demonstrate well-known hydrodynamical features such as turbulence and instabilities. We test ALFVN with standard test problems like the Linear Waves Test and the Sod Shock Tube. ALFVN is modular by design. The reconstruction step, Riemann solver, and the numerical integration method which dictates the overarching structure can all be swapped out individually while keeping the rest of the code intact. We hope to explore and compare various options available for each of these components. For reconstruction, we will experiment with donor cell, piecewise linear, and piecewise parabolic interpolations. For numerical integration, we will compare forward Euler, van Leer 2, and Runge-Kutta 2. We will also test LLF (Local Lax-Friedrich) and HLLE (Harten-Lax-van Leer-Einfeldt) methods for the Riemann solver. In each of these combinations, we supply ALFVN with the same initial condition and discuss the output in terms of their accuracy and efficiency. Since ALFVN is written to be easily run on a home computer for demonstration purposes, it benefits to know the limitations and runtime of various options in each component of a hydrodynamics code. |
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JP11.00123: Dynamics in an Atmospheric Pressure Plasma Jet Dzafer Camdzic, Adam D Light The dynamical regimes of atmospheric pressure plasma jets remain relatively unexplored. While a small number of studies have observed chaotic behavior in jets, very little is known about dynamical transitions in these systems. Better understanding of the possible dynamical regimes will help constrain the large parameter space available for applications. We measure the temporal behavior of the electrode current in a DC-driven, coaxial dielectric barrier jet using argon. Analysis of Poincaré recurrences in a time series provides a quantitative means to classify dynamics and identify transitions in a complex system. We use recurrence quantification analysis (RQA) to explore dynamical variations in the discharge current for a simple jet system. |
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JP11.00124: Far-Field Spot Reshaping with Phase-Front Optics for Plasma Experiments Kenyon J Carlson, John A Marozas, Jon D Zuegel Today, in the high-intensity lasers used for plasma experiments, it is essential to have a controlled envelope for optical absorption in the target designs. Since the 1980s, distributed phase plates (DPP’s) have been widely used as far-field spot-shape control. This poster will describe the DPP design method with examples presented for the Helmholtz International Beamline for Extreme Fields Diode Pumped Optical Laser for Experiments (DiPOLE) 100X. The DiPOLE system plans an upgrade for controlled spot-shape illumination to achieve optimal high-intensity conditions for a variety of experiments at various target sizes. The objective of this project is to create three DPP’s crafted to shape 500-mm, 250-mm, and 100‑mm spots, respectively. Zhizhoo’ was the primary design tool. The contoured-glass DPP design tool Zhizhoo’ adapts to any coherent optical beamline to craft the quasi-random near-field phase optic capable of custom tailoring the prescribed spot-shape envelope on a target in the far field. Zhizhoo’ employs an advanced, adaptive Fourier-transform-based feedback loop with phase unwrapping to craft DPP’s. The DPP controls the distribution of speckle in the far field via phase-front control of the near field, which conforms to any requisite envelope of the laser facility. Detailed design elements such as spatial-frequency controls of the DPP phase object will be discussed and how they affect the design process. As a finished product, less than 1% error along the uniform profile was observed for the DiPOLE DPP designs. As a result of the high efficiency of these designs, DiPOLE will be able to conduct high-energy-density experiments with increased laser performance. |
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JP11.00125: Transport modeling of Alcator C-Mod H-mode Magnetic Field Scan Blake M Carter, Christopher G Holland, Nathan T Howard, Pablo Rodriguez-Fernandez, Dmitriy M Orlov The GACODE transport modeling suite is used to predict core temperature and density profiles |
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JP11.00126: Breakdown of Argon and Nitrogen inside a Microgap Driven at High Frequency Miguel E Castelan Hernandez, Stephen K Remillard, Seth M Woodwyk, William G Zywicki The high-frequency oscillation of free electrons in a microgap (gap size< 1mm) leads to gas breakdown when the driving electric field exceeds a threshold, Ebd. In these experiments, with microwave signals introduced into a re-entrant microwave resonator, Ebd for argon and nitrogen was measured over a wide range of pressures and microgap sizes. As gas pressure is reduced below atmospheric, two distinct gap size dependent behavioral pressure regimes are observed where plasma transitions from uniform breakdown within the gap at higher pressure, to a glow discharge outside of the gap at lower pressure. The transition between these two regimes predictably occurs when the size of the microgap exceeds the dimension where microgap boundary loss of the oscillating electrons can be expected, resulting in a simple power law relationship between the transition pressure and the microgap size. |
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JP11.00127: Investigating the density evolution after the L-H transition in Deuterium and Hydrogen plasmas Javier E Chiriboga, Lothar W Schmitz, Saskia Mordijck In tokamaks to achieve the high confinement (H-mode) necessary for beneficial fusion conditions, turbulent transport at the plasma edge is suppressed. This bifurcation from low (L-mode) to H-mode confinement results in the slow build up of steep temperature and density gradients at the plasma edge. In this poster we will be comparing the electron density evolution for hydrogen and deuterium at low and high starting electron density. We observe that at low density that density evolution at the plasma edge with respect to time is linear, whereas at higher density this evolution is non-linear. The electron density increases faster in the hydrogen plasma at low density, but saturates at a lower value than the deuterium plasma. We will extract the transport coefficients by matching spatial as well as temporal evolution of the electron density profile for all 4 experiments and compare these to expected transport scalings. |
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JP11.00128: Incorporating Quantum Electrons in Classical Calculations for Dense Plasmas Simran Chowdhry Ab initio quantum molecular dynamics ‘QMD’ and density functional theory codes albeit the most accurate currently, often prove to be computationally intractable for studying shock dynamics. The present work aims to develop a computationally feasible approach to modelling shocks in low-Z dense plasma with partially degenerate electrons by identifying and implementing an effective potential for classical molecular dynamics ‘CMD’ simulations. The effective potential, fitted using the pair correlation function derived from QMD data, is used to simulate the shock Hugoniot with the code LAMMPS, which is then compared to the improved QMD equation-of-state table. Initial studies were conducted for deuterium plasmas using the AIREBO-M potential, given its success in modelling high-pressure hydrocarbons in ICF ablators, and the fitted potentials. This is done for both the weak and strong shock regime, including shock propagation and its release into a vacuum, with an allowed Hugoniot deviation of 20%. Following this, transport coefficients and shock structure are investigated to further test the accuracy of the effective potential. |
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JP11.00129: An Experiment to Simulate Trapping and Detection of Radioactive Isotopes Produced in ICF Implosions Micah Christensen, Micah K Condie, Adam Brown, Mark E Yuly, James G McLean, Stephen J Padalino, Chad J Forrest, Thomas C Sangster, Sean P Regan It may be possible to measure the low energy nuclear cross sections of light ion reactions by trapping the reaction products from an ICF implosion and detecting their beta decays. To test this idea, an “exploding wire” experiment has been designed to simulate the expanding gas released in an ICF event. A copper plated tungsten foil was inserted into a vacuum chamber and activated with a deuteron beam via 65Cu(d, p)66Cu. A current pulse through the tungsten then vaporized the copper to create an expanding radioactive gas, simulating the gas behavior in the ICF target chamber following the laser shot. Attempts were made to capture some gas and detect the 66Cu beta decays using two trap designs, one using a getter and the other a turbopump. Both designs used the Short-Lived Isotope Counting System (SLICS), consisting of plastic scintillator phoswich detectors and fast electronics, to identify and count the beta particles. |
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JP11.00130: Simulations of a Hall thruster operating with different gas propellants Denisse Cordova Carrizales, Yevgeny Raitses, Jacob Simmonds Hall thrusters are among the most developed electric propulsion devices, allowing faster and cheaper space exploration than their chemically fueled counterparts. Xenon is commonly used as gas propellant for Hall thrusters because it is relatively easy to ionize and has a high atomic mass, allowing the thruster to achieve high specific impulses [1]. However, xenon is rare and expensive, motivating the exploration of other elemental and molecular propellants. Alternative propellants to Xenon including krypton, argon, and nitrogen have been experimentally pursued [2-4]. In this work, we use a 1-D fluid-kinetic hybrid code [5] to explore the efficiency of ionization of these alternative propellants in a Hall thruster. |
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JP11.00131: Coil Optimization for a Quasi-Helically Symmetric Stellarator Michael Couso, Andrew S Ware, Aaron Bader, Chris C Hegna Optimized coil configurations are developed for a quasi-helically symmetric stellarator using the FOCUS code [C. Zhu, et al., Plasma Phys. Contr. Fusion 60, 065008 (2018)]. Recent work has indicated that optimization of quasi-helical symmetry and minimization of the radial drift velocity can lead to configurations with improved neoclassical confinement and improved confinement of energetic particles [A. Bader, et al., J. Plasma Physics 85, 905850508 (2019)]. Preliminary coil configurations that both optimize the physics and meet engineering constraints have been obtained. In this work, the FOCUS code will be used to develop and analyze coil configurations for four-field and five-field period configurations with a set of poloidal field coils. The effects of different coil configurations on Ideal MHD stability, neoclassical transport and energetic particle confinement will be examined. This work will include optimization of a coil set for a midscale stellarator experiment and the development of a coil set for a reactor scale device. |
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JP11.00132: Comparing neutral density profiles between a spherical and regular aspect ratio tokamak Gordon Jameson J Crouse, Saskia Mordijck, Richard M Reksoatmodjo, Andrew Kirk In current-day magnetic confinement devices, the ionization of neutrals inside the separatrix contribute to the steep electron density profiles. However, in reactor regimes, neutrals will be ionized in the SOL, directly impacting the shape of the electron density profile [1]. The ionization of neutrals does not only have an impact on the electron density but can also act as an energy and momentum sink and directly affect the radiation by impurities. We use SOLPS-ITER to model a MAST H-mode discharge. We will extract the transport coefficients by matching the experimental midplane profiles. By having SOLPS match the experimental profiles, we will be able to self-consistently extract the neutral density profiles. The compactness of spherical tokamaks suggests that neutrals will penetrate deeper than in regular devices. Therefore, we will compare the neutral density profile characteristics in a spherical tokamak environment to those of a regular aspect ratio tokamak. |
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JP11.00133: Using machine learning to replace 3D particle-in-cell (PIC) simulation of nanocale vacuum channel transistors (NVCTs). Sarah V Crull, Jesse M Snelling, Gregory R Werner, John R Cary This work aims to use a neural network instead of PIC simulation to predict device characteristics of an NVCT. An NVCT is a nanoscale vacuum triode in which applying a voltage to the gate causes field-emitted electrons to travel from the emitter through the gate to the anode; such devices could replace solid-state transistors under extreme conditions (e.g., low/high temperatures, radiation, high voltage). 3D PIC simulations are expensive, so we investigate the use of neural networks to predict the results (gate current and anode current) of simulations as a small number of parameters (inputs to the neural network) are varied, including: gate-anode distance, gate-anode voltage, gate-emitter voltage, etc. We use PIC simulations to train the neural network, and to evaluate the neural network performance beyond the training data. |
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JP11.00134: Measurements of CECE/nT-phase spot size at ASDEX Upgrade Calvin Cummings, Rachel Bielajew, William Burke, Garrard D Conway, Pedro A Molina Cabrera, Pablo Rodriguez-Fernandez, Christian Yoo, Anne E White Turbulence is known to be responsible for anomalous transport in tokamaks, reducing energy confinement times and limiting reactor performance. The correlation electron cyclotron emission (CECE) and ne-Te cross-phase diagnostics installed on the ASDEX Upgrade (AUG) tokamak measure broadband, long wavelength (kθρs approximately <0.3) electron temperature and density fluctuations, yielding insight into turbulence-driven transport. The poloidal spot size, determined by focusing optics, is critical in determining the physical dimensions of the turbulence measured, with a smaller value of spot size yielding higher poloidal resolution in the measurement. To measure the spot size of the combined CECE/ ne-Te cross-phase diagnostic in use at AUG, an identical optical set up is constructed and tested at MIT. Here we present the details of the optical set up as well as the results of the tests to determine the spot size of these diagnostics. These measurements will enable a more accurate analysis of CECE and ne-Te cross-phase data and improve our understanding of turbulent fluctuations. |
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JP11.00135: COTSIM-based Feedforward Control Optimizer for Model-based Scenario Planning in NSTX-U David Dang, Brian R Leard, Tariq Rafiq, Eugenio Schuster By combining plasma-response predictive models and nonlinear optimization techniques, the scenario planning problem in tokamaks like NSTX-U can be written as a model-based, constrained, feedforward-control, optimization problem as originally proposed in [1]. In this optimization problem the time evolutions of actuators such as the powers of heating and current drive (H&CD) sources are determined by minimizing a cost function quantifying the distance between the actual and desired plasma state. The optimization problem, which admits any user-defined cost function, is solved subject to plasma-dynamics constraints, actuator constraints such as the maximum amount of H&CD power or the total plasma current ramp rate, and plasma-state constraints such as the minimum-value of the safety-factor profile or the maximum value of βN. The plasma-dynamics constraints for NSTX-U are provided in this work by the Control Oriented Transport SIMulator (COTSIM). The resulting optimization problem is solved by employing the Sequential Quadratic Programming (SQP) technique. The technique is illustrated by several scenario planning problems in NSTX-U. |
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JP11.00136: Ultrasound Doppler Velocimetry Measurements in the Princeton Magnetorotational Instability Experiment Svetlana Doroshevich, Yin Wang, Erik P Gilson, Fatima Ebrahimi, Hantao Ji, Jeremy Goodman The standard magnetorotational instability (SMRI) is widely believed to be responsible for the fast angular momentum transport in accretion discs. Nonetheless, its existence has never been identified unambiguously in astronomical observations or in laboratory experiments. By measuring the radial magnetic field, a recent study at Princeton Plasma Physics Laboratory shows evidence of SMRI in a modified Taylor-Couette device that uses liquid metal as the working fluid. This study is aimed at supporting these findings using velocity data measured by ultrasonic doppler velocimetry on the outer cylinder. Through the analysis of the average velocity field measured at different azimuthal angles, the radial velocity field is obtained. Further, the azimuthal structure of SMRI in the velocity field is obtained using modal analysis, the results of which are in good agreement with results obtained from magnetic field diagnostics. The growth of SMRI, as well as the time delay of its onset, are studied to understand the underlying mechanisms. |
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JP11.00137: A TriForce module for performing inline Hydrogen spectroscopy on the Princeton Reversed Field Configuration. Henri N Doucet The Princeton Reversed Field Configuration-2 (PFRC-2) is a rotating magnetic field-heated (RMF-heated) field reversed configuration (FRC) with the primary goal of reaching average ion temperatures of > 500 eV. Experimental measurement of electron temperatures via visible line emission has been performed on the PFRC-2, but the interpretation methods used result in variations of up to 50%. Integrated simulations including both the device and its diagnostics can inform the design of future experiments via time and resource-efficient exploration of the relevant parameter space. Proposed here is a supplemental module to the University of Rochester’s TriForce Library for Integrated Numerical Kinetics (TFLink), a particle-in-cell (PIC) code that has done preliminary integrated simulations of the PFRC-1 device. This module would allow for calculations of the Hydrogen radiation production in each computational cell to be performed inline, allowing for synthetic data collection, localized both spatially and temporally. These synthetic data are then compared to experimental data. |
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JP11.00138: Expected performance of the ITER core x-ray crystal spectrometer (XRCS-Core) diagnostic including sensitivity to alignment and tolerancing Collin Dunn, Novimir A Pablant, Robin Barnsley, Zhifeng Cheng, Maarten De Bock, Nathan B Bartlett, Jovany S Gallardy, Y. Yakusevitch The ITER core x-ray crystal spectrometer (XRCS-Core) has been simulated using advanced x-ray raytracing to study the effects of misalignment and thermal deformation on the performance of the diagnostic. The XRCS-Core system will detect x-rays produced by the introduced impurity Xe and the intrinsic impurity W and spatially resolve the ion temperature and toroidal velocity profiles. The diagnostic utilizes a novel design that employs highly oriented pyrolytic graphite (HOPG) pre-reflectors to allow the crystals and detectors to be placed behind the bio-shield, while still being able to view x-ray sightlines covering the full minor radius of the plasma. In the operation of ITER, thermal expansion is expected to cause parts of the diagnostic to undergo translation and/or rotation motion, leading to misalignments of the crystals from the HOPG pre-reflectors. The effect of these rotations and translations on the throughput and energy bandwidth of the system were modeled using the XICSRT raytracing code. The use of actuators to pivot the crystals to maintain system alignment during thermal variations has been examined. Requirements for engineering, installation and alignment tolerances have been quantified and will be used as part of the continuing design efforts. |
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JP11.00139: Experimental Measurements and Numerical Simulations of Bow Shocks in Supersonics Plasma Jets* Robert H Dwyer, Mark A Gilmore Recent experiments on the University of New Mexico's HelCat Dual Source Plasma Device have focused on understanding the dynamics of bow shocks of supersonic (M=3-5) plasma jets with a cylindrical object placed inside the HelCat vacuum chamber to disrupt the jet flow and form a bow shock. The HelCat chamber allows for a variety of diagnostics including probes, high speed imaging and spectrometry on cm spatial scales and microsecond temporal scales. The chamber also allows for the jets to be launched into varying background conditions including orthogonal magnetic fields, helicon plasmas and gas backfills. Parallel to the experimental work, the Perseus extended MHD code has been used to run models of the global dynamics of the shock experiment. This presentation will focus on the experimental measurements made so far as well as some of the insights gained using the numerical modelling in Perseus. |
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JP11.00140: Uncertainty Quantification for Machine Learning Models in Plasma Physics Laura Fang, Rory Conlin, Joseph A Abbate, Egemen Kolemen While several machine learning models exist for predicting future states of plasma, little work has been done to evaluate how reliable these models are, and how their accuracy varies with different inputs and plasma types. As most physics-based models of plasmas include many approximations, it is difficult to discern whether machines are learning the correct patterns, or if they are simply memorizing data. The ability to accurately predict plasma states is integral to achieving the control needed for a stable, high performance fusion reaction. We demonstrate methods to quantify the uncertainty of machine learning models, as well as methods to improve the predictive accuracy of existing models. We further describe methods to generate predictions and accurate uncertainty bounds for both existing models and newly developed ones. |
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JP11.00141: Adapting Trinity for Use in Stellarator Plasma Profile Predictions Sorah Fischer, William D Dorland, Michael C Zarnstorff, Tony Qian, Chesson Sipling, Santiago Lisa, Braden Buck, Nastassia Patnaik, Brian X Jiang, Wenxi Wu, Nathaniel Stauffer, Bharat K Medasani, Sreya Vangara The complexity of transport in high-temperature magnetized plasma used in fusion devices is due to particle fluctuations caused by turbulent effects including drifts, instabilities, and impurities. The complex origin of the turbulence effects and the magnitude of scales they traverse in time and space makes it difficult to correctly model the plasma profiles. |
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JP11.00142: Analyzing Thomson-Scattered Spectra from non-Maxwellian Velocity Distribution Functions in Multi-Species Plasmas Bryan Foo, Derek B Schaeffer, Peter V Heuer, William R Fox Electron and ion velocity distribution functions (VDFs) are important for understanding the dynamics occurring within nonlinear plasmas such as those of magnetized collisionless shocks. These VDFs can be measured with Thomson scattering diagnostics, but due to their non-Maxwellian nature, can be difficult to interpret with existing analysis tools. We present an open-source software that can be used to analyze the Thomson-scattered spectra of plasmas with non-Maxwellian VDFs. Using numerical methods, we forward-modeled arbitrary VDFs of multi-species plasmas to their corresponding Thomson-scattered spectra, using existing PlasmaPy code that handles strictly Maxwellian VDFs as a benchmark. This was then used as a foundation for studying an inversion algorithm to extract plasma parameters from spectra Thomson-scattered from arbitrary VDFs. The inversion algorithm was tested on PSC particle-in-cell (PIC) simulations of nonlinear multi-species plasmas with known VDFs and successfully reproduced the observed plasma parameters. |
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JP11.00143: Mapping of DIII-D Profile Data in OMAS Kyle Fossum, Sterling P Smith, Orso Meneghini A common task for any tokamak core transport interpretive analysis is the fitting of the kinetic profiles with a smooth curve. In One Modeling Framework for Integrated Tasks (OMFIT), the OMFITprofiles module has grown a large number of methods to fit the data with a curve. In addition, the OMFITprofiles module is able to fetch data from a variety of devices and data structures for fitting. One data type to which OMFITprofiles has not been completely adapted is the ITER Integrated Modeling and Analysis (IMAS) data structure, which should be able to handle any device and data format where the data is stored in the IMAS data schema. The Ordered Multidimensional Array Structure (OMAS) library (gafusion.github.io/omas) contains methods for converting data stored in MDS+ to the IMAS data structure. The ability to map DIII-D profile data is being added to the OMAS library, and the best default methods and parameters for OMFIT profile fitting are explored. |
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JP11.00144: Fabricating Novel Geometries of Low-Density GA-CH Aerogels Ethan J Frey, Wendi Sweet, Fred Elsner, Eduardo Marin, Reny Paguio, Jarrod Williams, Ragad Mohammed, Grayson Lovelace, Nicolas Vargas-Ayala Low density GA-CH and GA-CD aerogels have found applications in fusion experiments at NIF, OMEGA, and Z. However, these applications sometimes require unusual and precise geometries achievable only by machining, which is difficult given the fragile structure of low density (<50 mg/cc) GA-CH aerogels. In this work, we investigated two approaches to make GA-CH aerogels machinable: adding a removable wax and adding a leachable alumina coating. The wax was added using solvent exchange within the liquid GA-CH gel and the alumina coating was created using atomic layer deposition (ALD) techniques. 1-5 mm spherical voids were also created within the aerogels using beads that were subsequently leached. Samples were characterized using density measurements, scanning electron microscopy (SEM), and X-ray imaging. The ability to easily fabricate novel geometries of GA-CH aerogels opens the door to many inertial confinement fusion applications. |
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JP11.00145: X-ray raytracing of Bragg reflections from Highly Oriented Pyrolytic Graphite (HOPG) in support of the ITER XRCS-Core diagnostic Jovany S Gallardy, Novimir A Pablant, Yevgeniy V Yakusevich, Robin Barnsley, Nathan B Bartlett, Zhifeng Cheng, Maarten DeBock, Collin Dunn, Sapna Mishra The ITER core x-ray crystal spectrometer (XRCS-Core), which measures core profiles of the ion-temperature and toroidal rotation in ITER, is a primary diagnostic that provides critical measurements for the ITER physics program. The ITER spectrometer utilizes a novel design with Highly Oriented Pyrolytic Graphite (HOPG) pre-reflectors that allow the spectrometer to be placed 9 meters away from the device. A complete raytracing model has been developed for ITER to study the expected performance of the XRCS-Core diagnostic. As a result, a new x-ray raytracing model for Bragg reflections from Highly Oriented Pyrolytic Graphite (HOPG) has been created using the XICSRT raytracing code. A key component is the accurate and efficient modeling of reflections from the HOPG reflectors. A set of simple reflection models have been developed and their performance is evaluated and compared to previous modeling efforts. Additionally, a set of laboratory experiments have been designed to allow direct validation of the HOPG raytracing models. Simulations of the expected results for these experiments will be presented, which can be compared to future experimental measurements. |
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JP11.00146: UW-Madison table-top stellarator experiment - parameters and design Thomas Gallenberger, Michael J Gerard, Benedikt Geiger, Thomas G Kruger, Marcel D Granetzny, Ryan Albosta A new table-top stellarator experiment, based on initial work from [1], has been designed with one planar and one helical coil to produce closed flux surfaces with five-fold symmetry. Detailed field line following studies show the use of only two coils is possible since the average vertical magnetic field along the magnetic axis is approximately zero. The 3D shape of the helical coil has been optimized to produce a large plasma volume and sufficient space between the coils and the plasma vessel. The vessel will be a pentagonal glass structure with a circular cross-section made from off-the-shelf components. The design of the plasma vessel and coils has been modeled with SolidWorks, considering three windings of the helical coil. VMEC equilibria produced using these three windings and the planar coil demonstrate a rotational transform of 0.15, though significant regions of parameter space have been identified for further optimization. Considering currents of up to 3.3 kA per turn, the expected magnetic field strength will be 0.05 T. This will allow the stellarator to be used in table-top plasma heating experiments using helicon waves, which provide excellent power coupling to the plasma. |
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JP11.00147: Using a 64Cu source to test SLICS Emma Parker, Nicole Gindling, Stephen J Padalino, Kayla Andersen, Mark E Yuly The short-lived isotope counting system (SLICS) being built for the OMEGA laser facility at LLE requires short-lived radioisotopes, such as 64Cu, for testing purposes. Using the SUNY Geneseo neutron howitzer, which contains a Plutonium-Beryllium (Pu-Be) source, 63Cu was bombarded with water moderated thermal neutrons to produce 64Cu via the 63Cu(n,gamma) capture reaction.The likelihood of neutron capture was increased using the optimal radial distance. Once activated, the 64Cu decays 61.6% of the time producing a positron with an endpoint energy of 653 keV which annihilates with an electron to produce two back-to-back gamma rays with energies of 511 keV each. The daughter product, 64Ni, is formed in the first excited state. It promptly decays to the ground state of 64Ni emitting a 1345 keV gamma ray which is used to determine the activity of the Cu source using the Gamma-X low background gamma-ray counting station. The activated 64Cu decays 38.5% of the time to 64Zn in the ground state, producing an electron with an endpoint energy of 579 keV. The 12.7 hour half-life of 64Cu allowed its transport to Houghton College where its signature was measured as a background to 66Cu used in future experiments to simulate detection of radioisotopes produced in an ICF implosion. |
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JP11.00148: Hybrid simulation of Alfvén/ion cyclotron instability of a one-dimensional electromagnetic plasma Sara Gómez, Jamie Humberto Hoyos Barrios Most of the matter in the universe is in plasma state, however, its study through experimentation is not feasible due to the number of particles that are present in a system and that most of the plasma in universe is in outer space. Owing to this, the author explains how to simulate plasma using Hybrid Method, which means that electrons are going to be model as a mass-less fluid and ions as particles, to show a way to study this state of matter without interacting with it. This approach arose in order to model special plasmas, where ions and their kinetic effects dominate the phenomena of the system, while the effects of electrons weakly influence the motion of the system. With the aim of testing the functionality of the method, a one-dimensional electromagnetic simulation of Alfvén/ion-cyclotron waves was performed where it is shown how the dispersion relation and kinetic energy change with varying thermal velocity. |
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JP11.00149: Spatio-temporal variation of edge neutral pressure in the LAPD Elijah W Grimaldi, Troy A Carter, Patrick Pribyl, Shreekrishna Tripathi, Walter N Gekelman A recent upgrade to the plasma source of the Large Plasma Device (LAPD) at UCLA enables access to higher plasma density and temperature operation. As a result, the behavior of neutrals in the device has changed, going from a regime where the plasma is effectively transparent to neutrals (leading to little spatial variation in the neutral density) to a regime with a short neutral penetration length (and hence the potential for strong spatial variation of the neutral density). Ion gauges with millisecond response times are positioned at various axial locations along the Large Plasma Device. Each is on a plenum with a large conductance to the chamber, so within limits can measure rapid changes in local pressure. Results are presented for a wide variety of plasma conditions, including a comparison between static gas fill and fast gas puffing using a piezoelectric valve. Gas puffing at different axial locations changes the neutral dynamics of the plasma and the observed time dependence of pressure variation along the machine. Results of conductance calculations are used to improve the time resolution with plasma at the expense of signal to noise ratio. These results are combined with fast framing camera imaging of visible light from the end of the machine using a filter for a Helium I spectral line to attempt to deduce neutral behavior inside the plasma. |
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JP11.00150: Space Charge Limited Current for a Nonzero Injection Velocity in Multiple Geometries Jacob M Halpern, Adam M Darr, Sree Harsha N R, Allen L Garner Space charge limited current (SCLC), first derived at vacuum by Child and Langmuir [1], is the maximum current that can be transmitted across a diode at steady state. Several subsequent studies have derived SCLC for planar diodes with a nonzero initial velocity [2,3]. Recent work has applied variational calculus (VC) to derive SCLC for one-dimensional planar, cylindrical, and spherical geometries [4]. In this study, we extend VC to derive SCLC for these geometries for a nonzero injection velocity. We compare the results to other planar diodes with nonzero injection velocity. Consequences regarding the virtual cathode and future applications of this method and extensions using conformal mapping [5] to more complicated non-planar diodes will be discussed. |
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JP11.00151: The Effect of Externally Applied Magnetic Perturbations on NSTX Edge Turbulence Michael Hanson, Stewart J Zweben, Dmitriy M Orlov, Ahmed Diallo We report on a study of the structure and motion of the edge turbulence of NSTX when non-axisymmetric magnetic perturbations are applied. For this study, the turbulence that occurs in the presence of these perturbations is compared to the turbulence seen when these 3D fields are not present using imaging data from the gas puff imaging (GPI) diagnostic. When magnetic perturbations resonate with a particular magnetic surface, usually at the plasma edge, they are referred to as resonant magnetic perturbations (RMPs). RMPs can be used to mitigate damaging edge instabilities called edge localized modes (ELMs) that are found in the high confinement operating mode of tokamaks. The GPI diagnostic uses a puff of neutral deuterium gas to increase the local D-alpha emissions which allows for improved imaging of the edge turbulence. The imaging data consists of high speed movies of the plasma edge taken at 400,000 frames/second. Understanding how 3D fields effect edge transport will lead to a greater understanding of the plasma response to these 3D fields. |
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JP11.00152: Robustness of reduced quasilinear transport models as compared with fully nonlinear frameworks Eamon J Hartigan-O'Connor, Vinicius N Duarte, Jeff B Lestz Auxiliary heating, essential to bringing plasmas up to fusion temperatures, produces an inverted distribution function of a minority fast ion species that can strongly resonate with Alfvén waves and potentially cause global transport. In the study of fast ion redistribution, it is instructive to determine how far reduced approaches can be employed, in comparison with more comprehensive but numerically costly ones. To investigate this question in a simplified geometry, we focus on the 1D bump-on-tail problem. Previous studies (K. Ghantous et al, Phys. Plasmas 21, 032119 (2014)) used a quasilinear model that employed a diffusion equation with a heuristically prescribed rectangular resonance function as its broadened diffusion coefficient. In the present study, we use the theory recently developed by Duarte et al, [Phys. Plasmas 26, 120701 (2019)], which self-consistently derived an analytic expression for such a resonance function for marginally unstable modes. We simulate the quasilinear evolution of the distribution function and the mode amplitude in systems with different degrees of instability strength and collisionality. The results are compared against fully nonlinear simulations of the Vlasov equation for the same system. |
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JP11.00153: Target Fabrication for Pelletron Accelerator Experiments at SUNY Geneseo Noah Helburn, Michael Fabrizio, Kurtis A Fletcher Several target fabrication methods, including thermal evaporation of thin films, low energy ion implantation, and high-temperature surface diffusion, have been developed to prepare targets for experiments at the SUNY Geneseo 1.7 MV Pelletron Accelerator. A conventional high vacuum bell jar system is used to produce gold, copper, aluminum, and polyethylene thin films with thicknesses of approximately 1kÅ via thermal evaporation. Multilayer targets have been prepared for RBS depth profiling analysis using this technique. The 30-kV duoplasmatron ion source at the Low Energy Ion Facility enables ion implantation of argon in graphite and silicon substrates. A compact 1100°C tube oven is used to prepare targets with gas diffused into tantalum and other substrates by first heating the substrate under vacuum and then backfilling with the desired gas. Accelerator targets must be prepared to satisfy specific experimental requirements, and providing multiple techniques for target fabrication supports our investigations into RBS depth profiling, nuclear fusion reactions, and other accelerator-based projects. |
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JP11.00154: UV LED Triggered Spark Gap for Repeatable Nanosecond Pulses Brian L Henning, Adam D Light We present progress towards a UV (280nm) LED triggered spark gap as a cheap solution for a repeatable discharge in high voltage ns pulsed power sources. While spark gaps are the simplest high voltage switches, the discharges can have several microseconds of jitter. Alternative switches that hold off 10kV or more and provide less jitter can be cost prohibitive and difficult to obtain. By using pulsed emission from a UV LED, we hope to provide highly repeatable pre-ionization in the gap. This allows for controlled timing of the discharge and faster switching times. We present progress to date and details of the switching characteristics of the triggered gap. |
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JP11.00155: Modeling re-ionization and particle trajectories in the neutral beam injectors of the DIII-D Tokamak Jonas Hildebrand, Brendan J Crowley J. P. HILDEBRAND, Whitworth University, B. J. CROWLEY, General Atomics. Neutral beam systems for plasma heating in fusion devices require a source of plasma from which to extract ions. These ions are accelerated by a series of grids at high potentials before they pass through a neutralizer and are recombined through collisions with a gas. After this, they are injected into the tokamak to impart their energy into the plasma. However, there are background gas molecules that can cause re-ionization for a portion of the neutral beam and in the presence of a magnetic field, the ions can be deflected into various beamline components and cause damage. Here we present the results of a modeling study where particles are tracked from the ion source until they are either injected into the tokamak or collide with a beamline component. The results are used to predict potential damage and recommend mitigating actions that may include administrative limits or engineering solutions. |
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JP11.00156: Development of Tunable Resonant Trays for Dust Collection in Tokamaks Theophilus L Human, Alessandro Bortolon, Alexander Nagy During tokamak operations, a significant amount of erosion occurs on the plasma facing components. This results in the accumulation of dust primarily within the machine’s lower divertor. In large scale projects such as ITER, this poses a challenge for sustained fusion operations. We propose a solution for actively removing the accumulated material based on tuned resonant trays for the collection and displacement of this dust to discharge ports. Based on linear vibrating powder feeders implemented on the Impurity Powder Dropper [Nagy RSI 2018], these tunable trays offer a potential dust management solution during tokamak operations. The resonant response of key assembly components was modeled by computer simulations for multiple materials and geometric configurations. The modeled results were validated by dedicated bench top testing using a piezo drive and accelerometer combination in order to properly characterize the acoustic response of the system. Leveraging these results, a full model has been designed, scaled for installation on a mid-size tokamak, compatible with the constraints of a high vacuum (10-7 Torr) and high temperature (~400C) environment. This work aims to show that these trays are a cost effective, scalable, and enabling technology for future tokamak devices. |
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JP11.00157: Effect of neutral interactions in gyrokinetic simulations of single seeded blobs Emily Humble, Tess Bernard, Federico D Halpern, Rupak Mukherjee, Manaure Francisquez, Noah R Mandell, Gregory W Hammett, Ammar Hakim We have studied the effect of neutral interactions on seeded blob dynamics using the continuum gyrokinetic code Gkeyll. Blobs, coherent structures of enhanced pressure, arise in the scrape-off layer (SOL) of fusion devices due to the interchange instability. They are convected radially outward by an ExB force, occurring from charge polarization due to magnetic drifts. Understanding blob transport is important due to its effect on exhaust properties in the SOL. The magnitude of the ExB force and resulting acceleration depends on the various currents that can dampen the charge accumulation, including current due to inelastic neutral collisions. A kinetic model for neutral dynamics has been coupled to the gyrokinetic solver in Gkeyll and includes electron-impact ionization, charge exchange and wall recycling. In seeded blob simulations, scans were conducted in blob size, background density and temperature, and blob density and temperature, both without and with neutral interactions. Velocities of the blobs were measured and compared to predicted scalings. Blob compactness and thermal and kinetic energy was also studied. |
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JP11.00158: Development and Implementation of a Numerical Laser Energy-Deposition Model for the PSC particle-in-cell code Abdullah S Hyder, William R Fox, Derek B Schaeffer, Sophia Malko PSC, a particle-in-cell (PIC) code, is being used to directly simulate experiments involving high-energy-density (HED) plasma plumes. Such simulations are being used for fundamental plasma studies including collisionless magnetized shocks and magnetic reconnection. HED plasma plumes are formed in the laboratory by using high-intensity lasers which ablate solid-density targets. Previously in PSC, an ad hoc plasma heating operator was used to represent the heating of the plasma by the laser, which was manually fitted to match simulations with more well-developed laser absorption models (W. Fox, et al, Phys. Plasmas 2018). To expand the scope of experiments that the code can run, a numerically calculated ray-tracing laser energy-deposition model was developed for and implemented into PSC using existing theory on optical absorption by a plasma. The energy deposited per cell was benchmarked against DRACO, a radiation hydrodynamic model with a well-developed energy absorption model, for both shallow and highly oblique laser incidence angles. The numerical model for PSC was found to be in excellent agreement with DRACO and analytical solutions. |
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JP11.00159: Low-Cost 3D Printed Laser Shutter Emiko Ito, Keily Valdez Sereno, Scott Feister The automation industry is thriving. However, university laser laboratories don't have the level of automation that professional laboratories do, making them more inefficient. They often cannot afford to hire professional engineers to automate their systems. The main goal of this project is to create an automated device for a laser laboratory using undergraduate skills. We interviewed lab technicians and decided that a low-cost, motorized laser shutter for huge laser diameters could benefit scientists in their laboratories. We explored different computer hardware to drive the shutter, and decided on an Arduino for its low cost and ease-of-use. We iterated several times in developing the circuit, writing the code, 3D modeling the shutter itself and the 3D-printed circuit board, printing parts and then putting them all together. For network control of the shutter, we interfaced the device with the EPICS control system, an open standard in professional science laboratories. Our result is a working circuit with EPICS controls and documentation. This work is especially noteworthy as it was developed by an undergraduate. It can be replicated by anyone with little to no experience with electronics, and can be customized to their specific laser experiments. |
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JP11.00160: Continuous-Time Bayesian Estimation of Tokamak Plasma States Yunona Iwasaki, Rory Conlin, Joe Abbate, Egemen Kolemen A new machine learning algorithm has been developed to efficiently interpret plasma states from previous and current sensor data. This model addresses a limitation of existing data driven plasma profile prediction models, which rely on accurate sampling at fixed time intervals; in practice, such data is not readily available due to limitations on available diagnostics and noise. The proposed method uses a Bayesian framework to update model predictions at time steps when sensor data is available, and a neural network to continuously evolve predictions during intervals when information is unavailable. This model is more compatible with plasma data that is irregularly observed in both time and space, which enhances the accuracy of interpretation. This makes it a potentially useful tool for better control over plasma states in fusion devices. |
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JP11.00161: Simulating the effects of ion mass-to-charge ratios on the Kelvin-Helmholtz instability Ivan J Jane, Landry Horimbere The Kelvin-Helmholtz instability can occur in many different astrophysical plasma environments, such as at the Earth's magnetosphere, the accretion disks and jets of active galactic nuclei, and pulsars. These environments have ion-to-electron mass ratios that range from much less than unity in dusty plasma, to unity in relativistic electron-positron jets, to 1836 in ionospheric plasmas, to 10^4 and beyond in experimental heavy ion plasmas. We want to understand how the presence of ions affects the dynamics of the Kelvin-Helmholtz instability through a careful analytical treatment and with two-dimensional ZPIC particle-in-cell simulations. We vary the charge-to-mass ratio of the superimposed ions to determine how this affects the growth rate, particle acceleration, and magnetic and electric field generation of the instability. This is done by extracting the phase space distribution in both spatial dimensions as well as both the magnetic and electric field in real space from fully kinetic simulations. |
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JP11.00162: Computational Exploration of Non-Neutral Plasmas Andrew Jenkins, Kelly Fang, Abtin Ameri, Nuno F Loureiro Non-neutral plasmas possess several attractive qualities: they have long periods of confinement (Dubin 1999) and their temperature can be arbitrarily lowered without recombination (Malmberg 1977). If the temperature reaches a low enough point, thermal equilibrium states can be formed in which the plasma crystallizes (Malmberg 1977). These properties make non-neutral plasmas an interesting candidate for further exploration. We study the confinement and dynamics of a pure electron plasma through N-body computational simulations in 2D. We also investigate various confinement properties, such as how particles are lost as a function of time. In order to confine the plasmas, we explore the use of a quadrupole ion trap. The governing equations of this system comprises the equations of motion derived from Newtonian mechanics along with the equations of motion within the trap (March 2009). Through simulated cooling of the system, we are able to evolve the plasma to a state of thermal equilibrium in which symmetric configurations are formed. Without allowing for cooling, the number of electrons confined becomes inversely proportional to time. In the near future, we plan to advance our simulation to three dimensions and explore the confinement of these plasmas within other trap mechanisms. |
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JP11.00163: Development of a Computational Model for MHD Response of a Novel Vacuum Vessel to Disruption Events Using the MFEM Library Joseph Jerkins, Sara Ferry, Jeffrey P Freidberg, Ethan E Peterson, Myles Stapelberg, Dennis G Whyte
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JP11.00164: Implementing the Unscented Kalman Filter for Phase Unwrapping and Denoising of Shearing Interferometry Images Samantha Kapushy, Hannah R Hasson, Pierre-Alexandre Gourdain The Unscented Kalman Filter (UKF) is a robust signal processing tool that is computationally efficient and is able to provide accurate analysis despite a large amount of noise. It is often used to track object trajectories and has previously been applied to interferometry analysis. In this research, the UKF will be applied to plasma laser interferometry images. The UKF will be used to unwrap the interference fringes and simultaneously remove noise. The unwrapped phase will then be used to determine the electron density and spatial information. The use of the UKF and the associated algorithm follows “Practical phase unwrapping of interferometric fringes based on unscented Kalman filter technique” [1], which details the math involved in the UKF and its application to multiple interferograms from different experiments. This project seeks to devise a computer program that efficiently analyses plasma laser interferometry data with minimal error and little human interference. The success of this project will allow for rapid, precise analysis of plasma laser interferograms. |
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JP11.00165: Modelling 2D Plasma Drift-Wave Turbulence in Tokamaks Using the Dedalus Python Framework Ish Kaul, Gregory W Hammett Plasmas in fusion devices such as tokamaks undergo a chaotic process called turbulence which affects their performance by controlling the rate at which particles leak out of the magnetic trap. Understanding the dynamics of turbulent transport in tokamaks and its features such as zonal flows, is an extensive field of study. We have developed a code for pseudo-spectral simulations of 2D drift wave turbulence of tokamak plasma based on the Dedalus framework (dedalus-project.readthedocs.io), an open source MPI parallelized python code. We will first present the results of the simulations for a hydrodynamic vortex merger test case in the vorticity formulation of the 2D Navier Stokes Equations with viscosity. Next, we will show the results for the evolution of the Hasegawa-Mima equations and the Terry-Horton equations, along with their properties such as enstrophy and energy conservation in the zero-viscosity case. Self-generated zonal flows can strongly reduce turbulence. We will study the impact of various models of zonal flows on the nonlinear saturation level of turbulence, including a model of the strong neoclassical shielding of zonal flows in tokamaks. This code will be made publicly available. |
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JP11.00166: Finite-Beta Optimization of a Quasi-Helically Symmetric Stellarator Priya Keller, Andrew S Ware, Aaron Bader, John Schmitt An effort is underway to develop stellarator configurations that have good confinement of bulk ions and have good confinement of energetic particles. Optimization of quasi-helical symmetry and minimization of the radial drift velocity can lead to configurations with improved neoclassical confinement and improved confinement of energetic particles [A. Bader, et al., J. Plasma Physics 85, 905850508 (2019)]. In this work, finite-β effects such as Ideal MHD stability and self-consistent bootstrap current in these configurations are analyzed. A comparison of the self-consistent bootstrap current predicted by the BOOTSJ code [K.C. Shaing, et al., Phys. Fluids B1, 1663 (1989)] and that predicted by the SFINCS code [M. Landreman, et al., Phys. Plasmas 21, 042503 (2014)] will be undertaken. The Ideal MHD ballooning stability is examined using the COBRAVMEC code [R. Sanchez, et al., Comp. Phys. Comm. 135, 82 (2001)]. Configurations with different rotational transform profiles are explored to obtain configurations that are able to withstand the addition of bootstrap current at higher β. Full results and analysis will be presented. |
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JP11.00167: Cross campaign database comparison of the absolute calibration of the LLAMA diagnostic on DIII-D James Kennedy, Florian M. Laggner, Alessandro Bortolon, Aaron M Rosenthal, Tomas Odstrcil High temperature plasma diagnostics in tokamak reactors face several deteriorating agents, such as neutron fluxes, throughout operation campaigns. This can lead to signal degradation, which in turn affects the accuracy and precision of the measurements. The LLAMA (Lyman-α Measurement Apparatus) diagnostic at DIII-D measures the Lyman-α brightness across the plasma boundary to infer neutral deuterium density and ionization rate profiles. LLAMA uses absolute extreme ultraviolet (AXUV) photodiode arrays, which are prone to responsivity degradation when exposed to ultraviolet radiation and neutrons. In order to account for this degradation, LLAMA undergoes an absolute calibration both before and after a run campaign to maintain accuracy. For a better estimation of the calibration factor throughout the campaign, a cross campaign database of plasma parameters (electron density and temperature) and LLAMA raw signals has been assembled and correlated. The database enables tracking of AXUV detector degradation by analyzing LLAMA signal changes across similar plasma discharge conditions. Relative changes of the calibration factor can be studied by applying this method after every DIII-D experimental campaign. |
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JP11.00168: Exploring dynamical accessibility in MHD relaxation models Patrick S Kim, Adelle Wright A multi-region relaxed magnetohydrodynamic (MRxMHD) model is used to study the nonlinear evolution of internal modes in a cylindrical tokamak. In particular, we examine whether the Stepped Pressure Equilibrium Code (SPEC) can correctly recover the magnetic island structures, predicted by the implicit nonlinear plasma evolution in an MRxMHD model, for different discretizations of the q and pressure profiles. We compare the SPEC results to linear and nonlinear simulations performed using the initial-value extended MHD code, M3D-C1. These comparisons allow us to understand when a relaxation model can reach a lower energy state that is consistent with more complete physics models. Contrary to ideal MHD models, an MRxMHD model permits changes in the plasma topology caused by magnetic reconnection and can result in the formation of magnetic islands. Finally, we compare values like the total plasma current and volume-averaged beta calculated in SPEC to analytical results from an ideal MHD model, developing scalings to quantify the impact of different discretization schemes on the predicted plasma properties. |
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JP11.00169: Computational Study of a Possible Future Experiment Exploring Vishniac Unstable Blast Waves at ZEUS Julian Kinney, Matthew Trantham, R P Drake, Carolyn C Kuranz The Vishniac-Ryu decelerating shock instability is relevant in thin-shell astrophysical phenomena such as supernovae remnants and shock waves in supernova events. We use CRASH, a Eulerian radiation-hydrodynamics code developed at the University of Michigan to compare 2D radiation hydrodynamics simulations of laboratory created blast waves to past experimental and 1D computational results (Edens et al. 2010) evaluating blast wave dynamics and radiation characteristics. Then we use CRASH to explore a new experimental setup to produce Vishniac-unstable blast waves using the capabilities of a long-pulse laser at the University of Michigan's ZEUS facility. We will present a poster. |
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JP11.00170: Ion source studies for application to the DIII-D neutral beam system. Daniel A Klasing, Brendan J Crowley Neutral beam systems for plasma heating in fusion devices require a source of plasma from which to extract ions. These ions are then accelerated by a series of grids at high potentials before they pass through a neutralizer and are recombined through collisions with a gas and injected into a device to impart their energy into the plasma. The DIII-D facility currently uses neutral beam systems with ions supplied by a tungsten filament driven plasma. As in incandescent lightbulbs, these filaments have a very finite lifespan and they produce a stable plasma with a limited range of parameters. It is for this reason that this study investigates alternative plasma sources for use in neutral beams. In a tabletop scale apparatus the plasma produced by a tungsten filament source is characterized via Langmuir probe and spectroscopy. This data is used as a foundation to design an RF driven plasma source outputting a similarly characterized plasma which should provide a decreased failure rate, an increased possible parameter space and other engineering improvements. Additionally an alternative filament material, lanthanum hexaboride, is investigated with respect to its fabrication considerations and failure modes as compared to the tungsten and RF driven sources. |
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JP11.00171: Investigation of 3D perturbation fields in TCABR, ITER, and DIII-D tokamaks. Marlena N Kot, Dmitriy M Orlov, Gustavo P Canal, Felipe M Salvador, Andreas Wingen 3D perturbation fields are widely used for suppressing Edge Localized modes (ELMs) in H-mode tokamak discharges. DIII-D can apply n=1,2 and 3 magnetic perturbations using the existing I- and C-coil sets and up to n=6 using the planned M-coils. ITER's design includes three rows of 9 coils each and will use n=3 and n=4 fields for ELM suppression. The upgraded TCABR tokamak (R0 = 0.62 m, a = 0.2 m, B0 ≤ 1.1T, IP ≤ 100 kA, max. discharge duration of 100 ms) operated at the University of Sao Paulo, Brazil, will have 3 rows of 18 internal coils located on the Low Field side and 3 rows of 18 coils each situated on the center post. In this work, we study the effects on the edge plasma magnetic topology and the magnetic footprints on the divertor surfaces produced by the proposed TCA-BR non-axisymmetric coil sets using TRIP3D-SURFMN and M3D-C1 plasma response codes. The results from the application of low (n=3) and high (n>3) toroidal mode number perturbation fields from the TCA-BR coils are compared to the existing and proposed DIII-D coil sets as well as to the ITER ELM coils using a set of previously developed metrics. |
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JP11.00172: Performance Optimization of High Hartmann Number Magnetohydrodynamics Analysis Using OpenFOAM Code Vincent Galvan, Griffin Kowash, Isabella Marshall, Andrei Khodak, Daniel Suarez Cambra Accurate magnetohydrodynamic modeling of liquid metal flows is essential for developing proposed fusion technologies such as breeding blankets and protective liquid lithium layers for divertors. For that purpose, a new code [1] was developed using the OpenFOAM C++ library. Existing codes allowing MHD analysis at high Hartmann numbers require a very large number of iterations to converge. In this work, an attempt to accelerate convergence of the OpenFoam code is presented. Flows at high Hartmann numbers are simulated using time step preconditioning to achieve semi-implicit treatment of the Lorentz force source term. Results show expedited convergence times while maintaining expected accuracy within flow profiles. |
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JP11.00173: Transport Coefficient Sensitivities in a Semi-Analytic Model for MagLIF Yousef Lawrence, Ryan D McBride, Adam B Sefkow In magnetohydrodynamics the magnetic field is obtained from an induction equation derived from an Ohm’s law for the electric field rather than Maxwell’s equations. As a result, magnetic-field evolution is determined from source, diffusion, and advection terms involving the magnetic field, plasma parameters, and proportionality constants called “transport coefficients.”1 Thermal conduction in magnetized plasmas is also affected. The coefficients themselves have been the subject of repeated recalculation using various methods throughout the years. Using a semi-analytic MagLIF model (SAMM), 2 we compare various fits to the electron and ion transport coefficients provided by Braginskii,1 Epperlein, Haines,3 Ji, Held,4 and Davies et al.5 The choices modify magnetic flux losses caused by the Nernst thermoelectric effect and thermal conduction losses. We present results from a suite of simulations conducted to quantitatively compare the effects of the different fits on various values of interest, such as the fuel temperature over time and the total fusion yield. |
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JP11.00174: Stellarator Coil Optimization Supporting Multiple Magnetic Configurations Brandon F Lee, Elizabeth J Paul Effective and efficient stellarator optimization is of great interest to the nuclear fusion community. Our goal in this work is to develop techniques that can be used to design devices capable of supporting multiple magnetic configurations. We utilize PyPlasmaOpt, a Python package that couples coil and vacuum field optimization, as our base software. Our primary methods for adding flexibility to the coil design are adjusting the currents in the modular coils and adding control coils to the device. We find that changing the currents in the modular coils without the addition of control coils leads to flexible stellarators with complex coil shapes and minute plasma volumes. Adding control coils introduces enough degrees of freedom to achieve multiple magnetic configurations, maintain reasonable coil shapes and low quasisymmetry error, and create larger plasma volumes. We add quadratic flux minimizing surfaces to the optimizations to increase the volumes further. Overall, we achieve greater flexibility by accounting for multiple magnetic configurations during the design. |
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JP11.00175: Rapid Evaporation of Activated Material for Detector Testing Vizma Leimanis, Jessica Dawson, James G McLean, Stephen J Padalino, Nicole Gindling, Kayla Andersen, Emma Parker, Micah Christensen, Adam Brown, Micah K Condie, Mark E Yuly The Short-Lived Isotope Counting System (SLICS) is being developed to measure radioactive fusion reaction products created in the Laboratory for Laser Energetics Omega facility with post-shot half-lives on the order of one second. SLICS was tested with a simulated ICF target designed to rapidly evaporate copper after deuteron activation in SUNY Geneseo's Pelletron accelerator. Copper was chosen due to its favorable half-life, cross-section, and abundance of Cu-66. Targets were made by electroplating a layer of copper onto tungsten ribbons. The copper was then evaporated from each target by rapidly heating it with a 100A current; SLICS then captured a portion of the copper evaporate and counted beta particles emitted from the Cu-66 to determine its activity. Several experimental trials were performed to investigate the optimal copper thickness for SLICS testing. It was found that a 25μm copper layer was thin enough to evaporate effectively and thick enough to stop the deuterons before they reached the tungsten. Thermal conduction between the tungsten and copper appeared to be the primary heating mode, but the role of radiative heating in later evaporation stages was also investigated. |
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JP11.00176: A new collision module for predicting divertor heat flux in axisymmetric discharges Joshua D Lewis, Andreas Wingen, Dmitriy M Orlov, Matthias Knolker Particles in fusion plasmas carry immense heat flux to the divertor targets in tokamak fusion devices. In future tokamaks, including ITER, this heat flux is predicted to exceed the limits of the chosen material, tungsten. Predicting the heat flux distribution is a goal of active research for current and future devices. A model was developed (Wingen, et al 2021 Nucl. Fusion 61 016018) based on an ion and electron guiding center drift approximation to simulate convective heat flux in perturbed plasmas. The model focuses on non-axisymmetric, perturbed plasmas, neglecting inter particle collisions. For this reason, the model does not reproduce the correct divertor heat flux profile, an Eich profile (Eich, et al 2011 Phys. Rev. Lett. 107 215001), in an unperturbed axisymmetric case. A collision module has been developed in the MAFOT orbit tracing code that allows for collisional particle transport across the separatrix. Using this module, the divertor heat flux profile for an axisymmetric discharge will be simulated and compared to an Eich profile. The heat flux layer width will be determined and compared with experimental observations from the DIII-D tokamak. |
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JP11.00177: Electromagnetic Extension to Ramo's Theorem Dion Li, David Chernin, Yue-Ying Lau Ramo's theorem, or the Ramo-Shockley theorem (RS) [1,2], describes the current induced on perfect conductors by the motion of nearby charges, and is a foundational result in vacuum electronics, discharge physics, and semiconductor devices. The classical theorem ignores relativistic and radiative effects and assumes that the fields are quasi-static. This paper demonstrates, for the first time, how RS is modified by electromagnetic and relativistic effects. Explicit, closed form analytic solutions of Maxwell's equations for the induced current distribution on conducting plates due to the motion of a line charge are presented. These solutions were verified by several methods, including particle-in-cell simulations. Novel features are accounted for that are absent in the classical RS: electromagnetic transients produced by the sudden acceleration of charge, the generation of an electromagnetic shock when a charge strikes a conductor, and the reflections of electromagnetic waves by the conductors. Applications of these new findings and further extensions will be presented. |
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JP11.00178: Investigation of ion incident angle and sheath profile in linear plasma devices Zihan Lin, Shota Abe, Bruce E Koel, Andrew H Liu High momentum flux in the divertor plasma of a fusion reactor causes surface erosion by sputtering, which reduces the lifetime of the plasma-facing component (PFC) and degrades plasma performance. The motion of boundary plasma particles in the collisionless sheath is guided by E and B fields before striking the divertor surface. Important parameters that govern the plasma-materials interactions (PMI) are incident angle, particle energy, and surface structure. The present study focuses on linear plasma devices (DIONISOS, PISCES-A, and Magnum-PSI) assuming 45°-88° B field angle at the target surface measured from the surface normal (0°). A collisionless kinetic model was used to calculate the incident polar and azimuthal ion angle distributions (IADs) of hydrogen, deuterium, and helium under sheath potential profile assumptions considering the classical Debye sheath and/or magnetic presheath. Microtrench samples for experimental IAD verification are designed using a Monte Carlo micro-patterning and roughness (MPR) code simulating erosion patterns of tracer materials on microtrench surfaces due to physical sputtering for expected IADs. The experimental verification of IADs validates the assumptions of the sheath modeling used in the IAD calculations. |
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JP11.00179: Calculation of Incident Ion Angle Distributions, Surface Erosion, and Material Migration at the NSTX-U Divertor1 Andrew Liu, Zihan Lin, Shota Abe, Bruce E Koel Plasma-material interactions (PMI) pose a significant threat to the viability of future tokamak fusion reactors. Surface roughness of plasma-facing components (PFCs) can trap impurity materials and T, posing plasma confinement degradation and radioactive inventory concerns. The surface structure also affects PFC erosion due to the ion incident angle dependence of physical sputtering, trapping of sputtered materials, and ion shadowing effects. In this research, a collisionless kinetic model was used to calculate the incident polar and azimuthal ion angle distributions (IADs) under sheath potential profiles expected for the NSTX-U divertor. Calculated IADs were input into a Monte Carlo micro-patterning and roughness (MPR) code to simulate the surface erosion and material migration. MPR input geometries ranged from analytically produced rough surfaces to optical confocal microscopy data of a NSTX-U graphite tile surface, which was exposed to 1138 L- and H-mode discharges (845 s total exposure time) [1]. The calculation results will be verified with Al concentration maps measured by scanning Auger microscopy (SAM). These calculations of IADs, surface erosion, and surface migration will be extended to the latest NSTX-U plasma and divertor configurations, such as fish-scale surfaces. [1] C.H. Skinner, et al., Nucl. Mater. Energy 18 (2019) 35. |
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JP11.00180: Oxygen Monitoring in Xylene NTOF Detectors Emily C Benton, Alexander Ball, Hunter Louscher, Aidan Cheeseman, Matthew Signor, Stephan Padalino Xylene scintillators are used to perform neutron time of flight measurements at LLE. Oxygen is dissolved in the xylene to reduce the scintillation decay time and improve timing response. Currently, there is no way to monitor the oxygen level in the detector. Using cosmic ray muons as a free and safe surrogate for neutron radiation, variations in muon scintillation waveforms are hoped to predict the oxygen level and xylene quality in situ without breaking the hermetic seal of the detector. Nuclear Magnetic Resonance (NMR) spectroscopy is being used to identify oxidation reactions degrading the scintillator. This data gives an indication for when the scintillator fluid should be changed. These studies are hoped to lead to an understanding of the oxidation chemistry of the scintillator. |
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JP11.00181: Detection of Hydrated Electrons at Liquid-Plasma Interface Using Total Internal Reflection Absorption Spectroscopy Quinna Phillips, Shalese M Lovell, Adam D Light
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JP11.00182: Verification and Validation of OpenFOAM Magnetohydrodynamics Code for Fusion Relevant Flows Vincent Galvan, Griffin Kowash, Isabella Marshall, Daniel Suarez Cambra, Andrei Khodak
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JP11.00183: Studies of the New Series of Gyrotrons Installed in DIII-D Electron Cyclotron Heating and Current Drive System Arthur G Mazzeo, James Anderson, Kurt Zeller, Perry Nesbet, Yuri Gorelov, Antonio Torrezan, Monica Blank, Kevin Felch, John Lohr, Mirela Cengher The DIII-D Electron Cyclotron Heating and Current Drive system (ECH/ECCD) recently added two 110 GHz gyrotrons in a new series produced by Communications and Power Industries, bringing the total number of installed gyrotrons to four. The performance of the new gyrotrons was studied. One of the new gyrotrons supports plasma experiments together with two other gyrotrons, while the other was installed and is in the process of being conditioned to long pulse and high power. We are presenting the results of the measurements of the generated frequency versus time and voltage, peak power density in the collector (less than 600 W/cm2 limit), power loss in the collector support (less than 20 kW limit) and azimuthal distribution, quality of the generated RF beam, and mode content in the transmission line. The infrared (IR) image processing for mode content measurement was optimized. |
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JP11.00184: COTSIM-based Gain Optimizer for Feedback Control of Advanced Scenarios in NSTX-U Yafet Menjetta, Hassan R Al Khawaldeh, Tariq Rafiq, Eugenio Schuster An optimizer has been developed to tune the gains of fixed-structure scenario controllers in NSTX-U. As indicated by their name, fixed-structure controllers have a well-defined structure but are functions of to-be-tuned gains. This is the case, for instance, of the widely used Proportional-Integral-Derivative (PID) controller, which is usually empirically tuned. As alternative, a more systematic approach to gain tuning is proposed in this work by selecting the gains based on a predefined, user-defined, optimization criterion. This criterion is expressed in terms of a to-be-minimized cost function weighing different metrics associated with closed-loop control performance such as tracking overshoot/undershoot, rise times, disturbance rejection, and steady-state tracking error. This optimization approach is enabled by closed-loop simulations carried out by using the Control Oriented Transport SIMulator (COTSIM) for NSTX-U, which is in turn wrapped around an optimizer based on the Sequential Quadratic Programming (SQP) technique. SQP is capable of solving arbitrary nonlinear optimization problems while handling constraints on the to-be-optimized parameters. The effectiveness of the method is illustrated for several scenario-control objectives. |
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JP11.00185: MATLAB App For Image Processing and Spectral Line Analysis Devin P Merrell, Shurik Yatom
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JP11.00186: Modeling the benefits of deploying thermal storage coupled to early commercial fusion reactors in a renewables-dominated grid Nigel K Mesta, Jacob Schwartz, Egemen Kolemen Fusion power plants will be deployed for commercial use in the 2030s at the earliest. Electrical grids already have significant intermittent wind and solar generation and their proportion will only increase over the coming decades. These must be balanced on an hour-to-hour and day-to-day basis to meet grid demand. Fusion power plants paired with thermal storage systems could provide an attractive complement to an otherwise solar- and wind-dominated grid. As a high-capital-cost component, it may be best to run the fusion core continuously. Adding a thermal storage solution would allow for continuous power generation while temporally shifting its deployment to maximize revenue based on the instantaneous demand. In addition, it is possible that the first commercial reactors will suffer frequent unplanned outages. We construct a linear programming model of a fusion power plant with an attached thermal storage system using estimated hourly electricity price series for a 2030s-era wind-dominated grid. We study whether adding thermal storage to a fusion reactor can mitigate losses in availability associated with unexpected shutdowns and increase profits. This model can also constrain the maximum cost of a reactor that must be profitable on an individual basis, given the assumed price series. |
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JP11.00187: Design of an Interferometer to Measure Electron Density in Atmospheric Pressure Plasma Benjamin Modlin, Brian L Henning, Adam D Light As a cost-effective way to measure electron density in atmospheric pressure plasmas, we explore optical interferometry using a continuous wave laser and lock-in detection. We present a Nomarski-type geometry designed to minimize sensitivity to inter-path vibrations and allow for future measurements with pulsed light. Typical electron densities of atmospheric pressure plasma jets range down to approximately 10^{12}/cc, which corresponds to a phase shift of only a few microradians in 632.8nm light. In order to increase our sensitivity to this small change, we drive the plasma with oscillating high voltage at 40 kHz and use that as our reference signal for phase-sensitive detection. We present the current design, preliminary results, and plans for upgrading the diagnostic in the future. |
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JP11.00188: Measurement of Electron Temperature in High Energy Density Magnetic Reconnection Experiments Jacob M Molina, Derek B Schaeffer, William R Fox The conversion of magnetic field energy to bulk plasma kinetic energy via magnetic reconnection is a ubiquitous process throughout astrophysical and laboratory plasmas. For large-scale and low-dissipation systems, fast reconnection can lead to the breakup of the current sheet into magnetic islands, but many questions about this process remain unanswered. Experiments at large laser facilities are able to create these conditions by colliding two plumes of expanding plasmas with embedded magnetic fields generated through the Biermann battery effect. Self-emitted x-ray bremsstrahlung radiation can then be utilized to diagnose fundamental plasma parameters. By passing these x-rays through a gated pinhole array of varying filter materials, we are able to extract electron temperature though a novel diagnostic technique [1]. We make use of these results to study the evolution of electron temperature in fast reconnecting plasmas. Additionally, we present an automated pipeline that was developed for our analysis; the development of which was necessitated by the large volume of dissimilar data sets used in our measurements, and serves to calibrate and congruently isolate the x-ray data from any two given pinholes. 1. D. B. Schaeffer et al. Review of Scientific Instruments 92, 043524 (2021) |
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JP11.00189: Measurement of the thermal state at the change in the frequency of polarity switching in the PK-4 Experiment Jeremiah D Williams, William C Morrison, Lori C Scott, Uwe Konopka, Edward E Thomas, Eva Kostadinova, Lorin S Matthews, Truell W Hyde, Mikhail Pustylnik, Hubertus Thomas The behavior micron-sized particles (dust) in a plasma system are of great interest, both as a model system for studying a wide range of physics and in practical applications. In ground-based experiments, the high mass of the dust leads to sedimentation effects. To reduce sedimentation effects, it is necessary to perform experiments in a microgravity environment, such as in the ISS based experiment facility "Plasma-Kristall-4" ("PK-4"). In the PK-4 facility, particles are injected into a dc glow discharge plasma and flow along an axial electric field. Upon the application of polarity switching (a periodic oscillation of the electric field), a sudden change in the bulk motion and spatial ordering of the dust is observed. This poster will present the results of a study of the thermal state of dust particles within the PK-4 experiment as the frequency of polarity switching is varied. |
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JP11.00190: Influence of parallel flows on drift wave turbulence in LAPD Leo Murphy, Saskia Mordijck, Troy A Carter In experiments at UCLA's Large Plasma Device (LAPD), we find a linear correlation between the amplitude of density fluctuations and the local density gradient, with no correlation observed between potential fluctuations and the local density gradient. In these experiments, the gas prefill and the cathode current were varied, allowing modification of the local density gradient at similar collisionalities and temperatures. Farther out, the introduction of an electron temperature gradient dampens the density fluctuations, destroying the correlation with the local density gradient, as predicted for a small ratio of electron temperature gradient to density gradient. Interestingly, a correlation between the potential fluctuations and the local density gradient is found, which was absent when no temperature gradient was present. We also observe a bifurcation in the potential fluctuations because of a difference in the parallel flow, which we plan to explore further in this poster. The parallel flow is linked to the parallel current, which is a critical component in driving resistive drift waves and we find that, with the differences in prefill and cathode current, this flow can change direction. |
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JP11.00191: Evolution of Isotopic Purity During Hydrogen Campaign in DIII-D Zoe Noble, Robert Wilcox, Colin Chrystal, Genevieve H DeGrandchamp, Shaun R Haskey, William W Heidbrink, George R McKee A recent hydrogen campaign at DIII-D involved switching the dominant hydrogenic fuelling species from deuterium to hydrogen and then back to deuterium. Due to strict isotopic purity constraints, efforts were put towards conditioning the walls using multiple actuators. Connections between isotopic ratios in the core and diverter of the tokamak and various experimental inputs were studied, including plasma shape, gas puff, glow time, vessel baking, boronization, and heating power. Three primary diagnostics were used: midplane spectroscopy for the measurements in the plasma core, a high resolution multi-chord diverter spectrometer with multiple view chords along the diverter, and a neutron scintillator to measure neutron generation to obtain a volume averaged concentration of the deuterium. |
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JP11.00192: Electrostatic Energy Analyzer and Gas Stripping Cell to Measure Ion Temperature in the PFRC-2 Matthew N Notis, Alan H Glasser, Samuel A Cohen, Shota Abe We describe a diagnostic to analyze the energy distribution of neutrals exiting RMFo-heated PFRC-2 plasmas. Energetic escaping neutrals, sourced primarily by charge exchange reactions of cold neutrals with energetic ions, first pass through a gas (H2) stripping cell, becoming partially ionized. The ions formed then enter a 90° curved-plate electrostatic ion energy analyzer (IEA), and those of the selected energy strike a Channeltron electron multiplier. The IEA is predicted to have a resolution of approximately 5%. To obtain a better estimate of the energy resolution, the IEA will be calibrated with an ion beam of known energy. The ionization efficiency of the stripping cell is predicted to be below 10% for H2 gas. Although the efficiency varies with the energy of incoming neutrals, this variation should not greatly influence our measured values of ion temperature. The RMFo heating mechanism is predicted to produce energy distributions unequal in the directions parallel and anti-parallel to the plasma current. Modeling the two energy distributions is being performed with a Hamiltonian single-particle code. |
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JP11.00193: COTSIM-based Numerical Solver for the Steady State Condition in Tokamak Plasmas Elizabeth Nuzzi, Zibo Wang, Sai Tej Paruchuri, Hexiang Wang, Tariq Rafiq, Eugenio Schuster Determining the steady-state condition of a tokamak plasma given fixed total plasma current, line-average density, heating and current-drive powers, and plasma shape is usually of high interest at the moment of developing a plasma scenario. A numerical solver has been developed in this work to provide such steady-state condition. The considered model, which is embedded in the Control Oriented Transport SIMulator (COTSIM), combines the Magnetic Diffusion Equation (MDE) with either semi-empirical scaling laws or transport equations for the electron density and temperature profiles. Imposing steady-state conditions to this model results in a Two-Point Boundary Value (TPBV) problem. The TPBV problem is solved by combining the finite-difference discretization technique with the Newton-Raphson method. Not only the plasma shape (which can always be regulated by external coils) but the whole magnetohydrodynamic (MHD) equilibrium are assumed fixed while solving the TPBV. The nonlinear dependence between MHD equilibrium and plasma state could be taken into account by combining an equilibrium solver with the proposed TPBV problem solver in a Piccard-iteration fashion. This approach would guarantee a steady-state plasma condition consistent with the MHD equilibrium. The proposed numerical method is illustrated by several representative cases. |
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JP11.00194: Effect of an electron beam on dust charge and ion motion a plasma Jeremiah D Williams, Austin O'Quinn, Dustin L Sanford, Katrina Vermillion, Lorin S Matthews, Truell W Hyde The kinetic effects on the dust particles in a plasma crystal locally irradiated by a narrow, pulsed electron beam (EB) with energies from 10 – 15 keV [C.M. Ticoş, et. al., Plasma Phys. Control. Fusion 62, 025003 (2020)] have shown that the EB pushes the dust particles in the irradiation zone, leading to both laminar and turbulent flow. Molecular dynamic simulations of this interaction have been able to reproduce many of the observed experimental results when considering a time-averaged electron beam irradiating the dust particles. However, simulations that include the pulsed nature of the EB do not. To address this, we consider the impact that the modulated electron beam has on the dust charge and the dynamics of the ions using the N-body simulation code DRIAD (Dynamic Response of Ions and Dust) [L. Matthews, et. al., Phys. Plasmas 27, 023703 (2020)]. Preliminary results will be presented. |
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JP11.00195: Correlations between NBI blips and ELM triggers in Tokamaks Samantha O'Sullivan, Andrew O Nelson, Alessandro Bortolon, Egemen Kolemen In tokamaks, the power injected with neutral beam injection (NBI) is often modulated at steady frequencies, providing 'blips' of power fueling the plasma core. Recent observations on DIII-D suggest these NBI power blips could play a role in triggering explosive instabilities called edge-localized modes (ELMs), which are responsible for intense transient heat fluxes on the machine walls and help to flush particles out of the core region. Here we examine a range of DIII-D discharges to identify correlations between NBI blips and ELMs under various plasma conditions. Statistical techniques identify the plasma regimes showing the strongest correlation between these two transients , demonstrating the sensitivity of NBI-ELM triggering on plasma density, rotation, power and shape. In cases with strong NBI and ELM frequency and time correlations, we examine the experimental pedestal profiles as a function of NBI and ELM phase to shed light on the triggering method itself. We can use this information to learn about the physics of ELM triggering, potentially leading to further optimization of ELMing H-mode plasmas. |
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JP11.00196: A gyrokinetic model of lithium lined plasmas Elizabeth Perez, Manaure Francisquez A key challenge in magnetic confinement fusion is the interaction between the walls of a device and the high temperature plasma, as the walls can damage and reduce theplasma temperature. Adding lithium to plasma-facing components provides the oppor-tunity to replenish the metal surface as it becomes damaged, and significantly reducesrecycling, allowing the edge to operate at much higher temperatures. The goal of thisproject is to develop a gyrokinetic simulation of the scrape-off layer (SOL) of plasmas inlithium-lined tokamaks, such as PPPL's LTX. LTX is the first tokamak to implement fullyliquid lithium walls, which have been shown experimentally to support flat temperatureprofiles, with SOL temperatures exceeding 100 keV. Commonly used fluid SOL modelsand simulations are relatively affordable but unjustified in the high-temperature, largelycollisionless environment of LTX's SOL. In this work we instead develop a gyrokineticsimulation of an LTX-like SOL plasma and present the effect that LTX-like parametershave on potential profile formation, plasma fluxes at the wall. This project will supple-ment current understanding of the effect of lithium walls on plasma performance, withthe key benefit of providing a lower collisionality model. |
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JP11.00197: Coherent Diffraction Method for Imaging Dusty Plasma Water Ice Grains Geoffrey M Pomraning, Paul M Bellan Water ice grains spontaneously form in the Caltech ice dusty plasma experiment [1] which involves cryogenic (~190 K) neutrals, water vapor, and weak (~10-6) ionization. The ice grains have been imaged until now using a long-distance microscope lens—with a 3μm resolution limit—mounted on a camera. Reference [1] showed that ice grain size and ellipticity could be ascertained from diffraction patterns of a HeNe laser beam. Re-visiting diffraction methods, we aim to use the diffraction pattern to obtain a complete detailed image of the ice grains. This pattern on a screen is the absolute value of a 2D Fourier transform (FT) of the ice grain shape so phase information is lost. We will use the Fienup phase restoration method [2] where iterative numerical guesses restore the missing phase using the physical constraint that the image intensity is non-negative. By taking absolute values of FT's, we have demonstrated this method on synthetic diffraction patterns, first removing then recovering phase. Theoretical considerations indicate that this diffraction/Fienup restoration method should improve on the microscope lens resolution by an order of magnitude. |
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JP11.00198: Simulating the Solar Wind: The Firehose Instability in the Two-Fluid, Ten-Moment Model Jenniffer Profitt, Jason M TenBarge, James L Juno The solar wind is one of the best natural plasmas: it constantly emanates from the sun, expands into and saturates the heliosphere, and interacts with planets including Earth. However, relatively little is known with certainty about the solar wind, including the behavior of pressure and temperature anisotropy instabilities driven by its expansion. We study one such instability—the parallel firehose instability—using the Gkeyll framework's two-fluid, ten-moment model. In our simulation, we include more information about the electrons, including the full electron pressure tensor, to go beyond existing fluid models. To isolate the firehose instability, we initialize the simulation in the firehose unstable regime. We expand upon previous research using the local closure model by applying a novel gradient closure for the heat flux. We present results on comparisons of the simulated growth rate to linear kinetic theory, how the ten-moment limit of the firehose instability saturates, and compare the saturation and nonlinear dynamics to existing nonlinear, hybrid-kinetic simulations. |
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JP11.00199: Particle-in-cell modeling of a potential demonstration experiment for double pulse enhanced target normal sheath acceleration Nashad Rahman, Joseph R Smith, Gregory K Ngirmang, Chris Orban Ultra-intense lasers are a promising source of energetic ions for various applications. An interesting approach described in Ferri et al. argues from particle-in-cell simulations that using two laser pulses of half energy (half intensity) arriving with close to 45° angle of incidence is significantly more effective at accelerating ions than one pulse at full energy (full intensity). For a variety of reasons, at the time of this writing, there has not yet been a true experimental confirmation of this enhancement. In this paper, we perform 2D particle-in-cell simulations to examine if a millijoule class, 5*10^18 W cm−2 peak intensity laser system could be used for such a demonstration experiment. Laser systems in this class can operate at a kHz rate which should be helpful for addressing some of the challenges of performing this experiment. Despite investigating a 3.5 times lower intensity than Ferri et al. did, we find that the double pulse approach enhances the peak proton energy and the energy conversion to protons by a factor of about three compared to a single laser pulse with the same total laser energy. We also comment on the nature of the enhancement and describe simulations that examine how the enhancement may depend on the spatial or temporal alignment of the two pulses. |
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JP11.00200: Surface Evolution in Long-Term Simulations of Graphite Boronization Aaditya Rau, Sierra Jubin, Igor Kaganovich Boronization has been shown experimentally to improve deuterium retention in fusion devices, which in turn leads to improvements in device performance. Prior simulations of boronization of graphite, a common wall material, have used randomized initial atomic positions, thus a concrete understanding of amorphization processes in crystalline graphite is necessary. Thus, in this study, the molecular dynamics (MD) code LAMMPS was used to bombard a large graphite structure with atomic boron over a range of impact energies. Then, from the simulation output, the number densities of boron and carbon as a function of depth were extracted to use as a metric for accumulated amorphization over time. Simulations show that larger impact energies lead to a greater degree of amorphization, shown by the increase in crosslinking between layers. Furthermore, the relationship between impact energy and amorphization timescale was investigated. |
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JP11.00201: Physics-assisted Machine Learning Spectral Fitting for Thomson Scattering Experiments on an Extreme Ultraviolet Plasma Light Source Alyssa Rauschenberger, Marien Simeni Simeni, Ahmed Diallo Modern computer chips as well as the entire semiconductor industry rely on Extreme Ultraviolet Lithography (EUVL) at 13.5 nm ± 1% to create finer resolution features. In the industrial settings, the 13.5 nm photons are generated by a plasma following the interaction of 20-30 μm diameter molten tin droplets with focused CO2 pulsed laser beams running at kHz repetition rates. Although the 13.5 nm light generation process has already been comprehensively studied numerically, only a handful of experimental studies report simultaneous measurements of the plasma parameters relevant to the production of the highly charged ions Sn8+‒Sn14+ responsible for the EUV light. Time-resolved collective Thomson scattering measurements, probing simultaneously the electron and ion features would provide a complete picture of the physics at play. To prepare experimental data analysis, a Matlab-based machine learning fitting tool was developed for real-time inference of the electron density, electron temperature and average charge state from Thomson scattering experimental spectra. “Neural Net Fitting”, an artificial neural network application from Matlab is deployed in conjunction with the analytical expression of the Thomson scattering spectral density function to perform a supervised non-linear regression model for the fitting of the experimental data. |
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JP11.00202: Commissioning of a 300 GHz Microwave Interferometer on PHASMA Mohammad Farhan Rawnak, Prabhakar Srivastav, Ripudaman S Nirwan, Earl Scime A 300 GHz microwave interferometer system designed to measure the chord averaged electron density in the PHAse Space MApping (PHASMA) device has been installed and tested. A 300 GHz operating frequency was chosen since it is well above the cutoff frequency ~ 60 GHz of PHASMA, corresponding to an electron density ∼5×1019 m-3. An additional leg of the system will be installed during a future upgrade for coherent scattering measurements. The interferometer will be used to validate conventional Langmuir probe measurements while avoiding the issues of perturbations, probe tip erosion, and electrical noise pickup issues. The interferometer is configured as a conventional Michelson interferometer with a combination of HDPE lenses, a beam splitter, and metallic mirrors. A chirped-frequency source is used to create a refractive index phase shift. The design details, installation, testing, calibration, and initial measurement will be presented. |
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JP11.00203: Background Rates Outside the OMEGA-60 Target Chamber Seconds to Minutes After a High-Yield Shot Steven H Raymond, Tyler M Kowalewski, Mark E Yuly, Stephen J Padalino, Sean P Regan, Thomas C Sangster, Chad Forrest
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JP11.00204: Porting the GEM Gyrokinetic Turbulence Code fromFortran to C++ for Improved Performance and Portability Sophie M Redd, Stefan Tirkas, Yang Chen, Junyi Cheng, Qiheng Cai, Scott E Parker We port the GEM gyrokinetic turbulence code originally written in Fortran to C++ toimprove both portablility and performance. GEM is a comprehensive global electromagnetic gyrokinetic particle simulation[1]. We are converting the inner-time loop functions to C++first, eventually converting the entire code. In the intermediary, we employ a binding library to link Fortran and C++. A pointer allocation algorithm generalized to higher dimensions isimplemented for optimal multidimensional array indexing of Fortran global arrays in C++. We also remove the use of MPI in Fortran and call MPI with the MPI C++ library. Long term, we are preparing to run on future exascale computers such as Frontier and Aurora. In preliminary conversions, we see nearly identical performance between the pure Fortran codeand C++/Fortran hybrid code. There is some minor additional compile/link time when using both C++ and Fortran. Additionally, we will show recent optimization/performance results using OpenMP GPU offloading and discuss the methods used to optimize C++ for numerical analysis. |
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JP11.00205: Evaluating Professional Development For Teachers and Giving Them the Resources They Want and Need Amelia J Reilly, Shannon Greco, Eva Kostadinova, Arturo Dominguez There is a need for more people in the Plasma Science and Fusion Energy (PS&FE) workforce. Plasma Network for Outreach and Workforce (PlasmaNOW) is a project to bridge the gap in the educational pipeline for PS&FE by engaging students, volunteers, and educators in pre-college outreach activities. My portion of the Plasma-NOW project focuses on creating a standard of evaluation instruments to assess the usefulness of previous APS Science Teachers' Day workshops and other similar professional development programs. At Teachers' Day, teachers learn about plasma physics and fusion research and ways to incorporate these concepts in lesson plans and activities in the classroom. Using these evaluations we hope to identify which types of resources would be most useful for teachers and make these resources available on the PlasmaNOW website once it is launched. We will also modify the existing Teachers' Day resources to best fit the stated needs of the teachers. Finally, we plan to share the evaluation tools on the PlasmaNOW website as a set of metrics and best practices for assessment of other teacher professional development programs. By compiling these resources, we hope that teachers make use of them, and better incorporate PS&FE into the classroom. |
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JP11.00206: Using Rutherford Backscattering Spectroscopy depth profiling to characterize targets at SUNY Geneseo Jovahn A Roumell, Vincent D Picciotto, Rudolph N DiMura, Yuki Watariguchi, Charles G Freeman, Stephen J Padalino Rutherford Backscattering Spectroscopy (RBS) is an ion beam analytical technique that can be used to study the properties of thin films. In this technique, a beam of energetic protons or alpha particles is incident on the sample and the energy of the scattered ions is measured. The energy spectrum reveals characteristics about the sample including thickness and elemental composition. RBS can be further developed using a technique known as depth profiling, in which a more sophisticated fitting of the resulting energy spectrum is used to measure the concentration of dopants in the sample as a function of depth. At SUNY Geneseo, we have been performing RBS experiments using ion beams from our 1.7 MV Pelletron particle accelerator. RBS has been used to measure the elemental composition and thickness of various thin layers of copper and gold deposited on a silicon wafer using Geneseo's thin film evaporator. Other targets have been produced at Geneseo using thermal diffusion and ion implantation. The goal of these studies is to develop a technique to use RBS depth profiling to measure the energy spectrum of heavy ions accelerated from the rear side of a target illuminated with ultra-intense laser light. Funded in part by a grant from the DOE through the Laboratory of Laser Energetics. |
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JP11.00207: Characterizing Crystallization in a Complex Plasma Mason S Sake, Uwe Konopka Complex (dusty) plasmas are the mixture of electrons, ions, and neutral atoms with the addition of charged macroscopic dust particles of nanometer to micrometer size. These systems exhibit gaseous, fluidic, and crystal-like phases depending on the electrostatic and kinetic energies of the system. Previously, these systems have been characterized using spatial correlation functions and particle dynamics using particle tracking velocimetry (PTV). This article aims to expand on that work to further identify specific crystal structures such as face centered cubic (fcc) by calculating the rotational invariance maps from PTV data and directly from images. The later techniques have potential advantages for real time analysis and experimental control. We present a Python library package workflow for identifying the different phases; as well, we show preliminary results of the temporal evolution of crystal formation in a dusty plasma cross section. |
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JP11.00208: Development of high photon throughput, high spectral resolution spectrometers using holographic and Echelle diffraction gratings for high temperature plasmas Jacob G Schellpfeffer, Ryan Albosta, Benedikt Geiger, Pradyumna Rao Two single channel prototype spectrometers have been developed for photon starved applications in high temperature plasmas, where high photon throughput and high spectral resolution are required. The first spectrometer follows a conventional Czerny-Turner setup using lenses instead of mirrors, while the second one is based on a novel design that incorporates an Echelle diffraction grating in Littrow configuration. Both spectrometers have the same spectral resolution and utilize the same camera but use different focal lengths. While the Echelle spectrometer, operated at high orders of diffraction, achieves a high spectral resolution at moderate focal lengths it lacks the flexible nature of the Czerny-Turner spectrometer as Echelle diffraction gratings have to be operated at their fixed Blaze angle. However, our study shows that the Echelle spectrometer offers improved photon throughput compared to the Czerny-Turner spectrometer and considering the same f-number. This proves that the Echelle approach has a product of photon throughput and spectral resolution, which makes it a very interesting concept for applications in fusion energy science. |
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JP11.00209: Exploration of error fields and correction methods in the MUSE permanent magnet stellarator Dominic Seidita, Tony Qian, Amelia Chambliss, Caoxiang Zhu, Michael C Zarnstorff MUSE is a tabletop, permanent magnet stellarator currently being developed at PPPL that aims to create a quasi-axisymmetric magnetic field using simple coils. We explore methods to address deviations from the desired magnetic field of MUSE which may arise due to imperfections in assembly and material components. The primary method being explored is to correct the error fields by adjusting the position of the permanent magnet holders. To accomplish this, the FICUS and FIELDLINES codes are being used to generate a library of magnetic field deviations caused by modeled construction deviations. Once MUSE is constructed, the magnetic field will be mapped with an electron beam and compared to this library, and adjustments will be made to reduce the error fields. A secondary method that is being explored is to correct the error fields with trim coils. Multiple trim coil designs will be compared, and their efficacy in suppressing error fields for MUSE will be evaluated. We present a collection of possible construction deviations and their effects in addition to a perspective on the most effective correction techniques. |
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JP11.00210: Development and implementation of a 3D 6-tip mach probe arranged in an octahedral geometry on WiPPL device* Allyson M Sellner, Abdulgader Almagri, Karsten J McCollam, Mikhail Reyfman, John S Sarff, Cary B Forest, Jens Von Der Linden, Jason Sears, Setthivoine You, Haruhiko Himura Measurements and simulations show that plasma relaxation processes in the RFP drive and radially redistribute both current and momentum. To examine the momentum redistribution processes better, a new prototype Mach probe has been designed and tested to measure the 3D plasma flow. The probe consists of 6 molybdenum tips that are arranged on the flattened vertices of an octahedron made of BN. The probe has three coils wound on a BN bobbin to measure the equilibrium and fluctuating magnetic field. Multipole return electrodes at various distances from the tips will determine the optimum location for the return current so that plasma perturbation is minimized. The return electrodes will act as the floating reference for tip biasing. A new 6 channel power supply has been constructed to measure current collected by each tip and the return electrode with a set of voltage dividers. All 7 currents are connected to a 100 kHz isolation amplifier. The magnetic signals are integrated with a 250 kHz bandwidth. All signals are digitized at 1 MHz. Preliminary results, calibration, drawings and photos will be presented. |
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JP11.00211: Gas Impermeable coating using High Power Impulse Magnetron Sputtering for High Energy Density Physics Applications Cole Shank, Hongwei Xu, Priya Raman, Haibo Huang, Fred Elsner, Neal Rice High Power Impulse Magnetron Sputtering (HiPIMS) is a type of magnetron sputtering technique that is capable of producing high quality, smooth, ultra-dense coatings with superior adhesion to the substrate when compared to conventional DC Magnetron Sputtering (DCMS) technique. In HiPIMS, very short unipolar high power pulses are applied to the sputtering target at low duty cycles. These high power peak pulses result in an intense plasma in front of the magnetron target, which then leads to a high ion fraction of the sputtered material. These energetic ionized sputtered species lead to dense coating. There is huge demand for thin walled, gas impermeable metal capsules for High Energy Density (HED) applications. Currently, conventional DCMS technique is used to produce these thin walled, gas impermeable metal capsules with very low success rate. In this work we are exploring the possibility of using HiPIMS to create dense, gas impermeable capsules. A thorough HiPIMS process optimization for gas impermeability is carried out and the results would be correlated with ion fraction measurement on the substrate using G-QCM (Gridded Quartz Crystal Microbalance), cross-sectional SEM and Krypton leak tests. |
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JP11.00212: A Software Framework to Rapidly Determine the Onset of ITG Turbulence for Stellarator Optimization Chesson Sipling, Chesson S. Sipling, William D Dorland, Michael C Zarnstorff, Braden Buck, Brian X Jiang, Tony Qian, Michael Cole, Sorah Fischer, Nastassia Patnaik, Santiago Lisa, Nate Stauffer, Wenxi Wu Many of the software tools scientists use to understand stellarators are disconnected and computationally intensive. To combat this, we are working to "pipeline" together a set of fast stellarator codes to calculate properties such as magnetohydrodynamic equilibria, transport, turbulence, and the threshold for turbulence for a given device. In particular, we will concentrate on measuring the onset of Ion Temperature Gradient (ITG) turbulence via an optimized calculation of the linear critical gradient. Additionally, we hope to code intermediate scripts to allow this pipeline to be executed from Python. As we expand this framework, we will introduce additional codes in parallel, facilitating further customization and broader application. We hope this new software framework will accelerate the plasma community's understanding of stellarator turbulence, transport, and stability. With this tool in hand, we expect to develop new stellarator geometries with favorable properties. |
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JP11.00213: Diagnosing Magnetic Reconnection in Simulations of Tokamak Scrape-off Layer Reehan Siraj, Noah R Mandell, Nuno F Loureiro The Gkeyll code has recently demonstrated the first capability to simulate electromagnetic gyrokinetic turbulence in the tokamak scrape-off layer (SOL), so that fluctuations in the magnetic field are accounted for. Including these fluctuations means that there may be magnetic reconnection occurring in these simulations. However, diagnosing magnetic reconnection in these three-dimensional regimes can be very difficult. In this work we develop a set of analysis tools that can search for signatures of reconnection and suggest locations where it may be occurring. This will enable further study of reconnection in the SOL and its impact on SOL dynamics and transport. These analysis tools could also be applied to other systems with three-dimensional magnetic reconnection, such as the solar corona or other astrophysical plasma systems. |
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JP11.00214: Measurements of the sawtooth cycle and fluctuation-induced Hall electromotive force in MST tokamak plasmas Winston Solsrud, Noah C Hurst, Brett E Chapman, Abdulgader Almagri, Karsten J McCollam, John S Sarff The significance of the dynamo-like, fluctuation-induced Hall electromotive force (EMF) is investigated during the sawtooth crash in q(a) ~ 2.5 Madison Symmetric Torus (MST) tokamak plasmas (BT = 0.14 T, R=1.5 m, a = 0.5 m) using a probe covering r/a > 2/3. Previous experiments in MST reversed-field pinch plasmas as well as simulations of the resistive kink instability in high-performance tokamaks have shown that the Hall EMF, 〈J × B〉, could play a role during reconnection events. Here, we characterize the magnetic fluctuations generated during a sawtooth instability to evaluate the Hall EMF’s contribution in the sawtooth relaxation process. Using a generalized Ohm’s law, the parallel Hall EMF can be expressed in terms of flux-surface-averaged, correlated fluctuations. Initial results indicate that the Hall EMF is non-zero during the sawtooth crash but small compared to the inductive electric field. Magnetic fluctuations appear to be localized near the q = 2 surface, suggesting m/n = 2/1 mode activity. Significant probe/plasma interaction has prevented direct measurement of magnetic fluctuations near the q = 1 surface, and there is significant variation between relaxation events. Work supported by US DOE and WiPPL Team. |
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JP11.00215: Characterization and performance predictions of L-mode plasmas in the SPARC tokamak Benjamin F Spector, Pablo Rodriguez-Fernandez, Dennis G Whyte We present a methodology for consistently, reliably, and quickly predicting the performance of L-mode plasmas using high-fidelity transport models. We build on the GACODE suite of tools, in particular TGYRO, TGLF and NEO, and sweep both boundary conditions as well as plasma input parameters in search of optimal steady-state solutions which are in-line with empirical scaling laws. This is motivated by the lack of reliable models for the boundary condition, unlike the pedestal models that exist for H-mode. We also recommend several configurations of practical relevance to achieving consistent convergence. We evaluate our methods on the SPARC tokamak to assess the possibility of accessing breakeven and Q>2 in L-mode scenarios. |
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JP11.00216: Topological Data Analysis and its Application to Drift Wave Turbulence Sage Stanish, Saskia Mordijck, Benjamin Dudson, Sarah Day Anomalous transport is a critical phenomenon in plasmas and predicting its behavior will aid in the design of future fusion devices. Anomalous transport is the result of drift-wave turbulence driven by various gradients perpendicular to the magnetic field. Here we use Topological Data Analysis (TDA) to study the Hasegawa Wakatani (H-W) model, which captures key features of drift-wave turbulence. TDA has been made possible by recent advances in computing and theoretical mathematics and computes the topology of arbitrary data. The goal is to identify topological structures in the H-W model and link them to the physical mechanisms behind drift-wave turbulence. Previous work applying TDA to classical fluid mechanics such as Kolmogorov Flow and Rayleigh-Bénard Convection has been promising. The authors were able to identify periodicity in the flow patterns and classify all states of the systems uniquely using TDA metrics. In this poster we will apply similar techniques to simulations of the H-W model. We look to identify predictors of change in the turbulent transport characteristics and connect these to the traditional descriptions of turbulent flow. |
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JP11.00217: Evaluating stellarator configurations in a Zero-D Python application Nate Stauffer, Tony Qian, Braden Buck, Nastassia Patnaik, Chesson S. Sipling, Brian X Jiang, Wenxi Wu, Santiago Lisa, Sreya Vangara, Sorah Fischer, Bharat K Medasani, William D Dorland, Mike Zarnstorff Evaluating the performance of a proposed plasma confinement device without physical testing is imperative to the viability of nuclear fusion. Their construction is far too expensive to justify investing in a poor design, and nontrivial simulation codes are currently too bulky to be run practically without the use of a supercomputer. The intent of this work is to develop a Python application that can meaningfully simulate stellarator transport with some simplifications that allow it to run quickly on a home desktop computer. We will discuss those simplifications, basis calculations, and any assumptions necessary to the function of the program. Our code finds values of heating power, volume averaged density, and helium concentration yield maximum Q and minimum ISS-04 H confinement scaling for a given stellarator configuration (defined by user input design parameters). We present extensions of the 0-D model to include higher fidelity physics calculations and demonstrate their performance and impact on the assessments. |
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JP11.00218: Implementation of Radiation in the Systems Code FAROES Shayaan Subzwari, Jacob Schwartz, Egemen Kolemen Radiation is important for power balance in tokamaks and for fusion devices in general. In the case of tokamaks, the main modalities are Bremsstrahlung, synchrotron, and impurity radiation. Bremsstrahlung is caused by electron-ion collisions, synchrotron radiation is due to emissions from electrons in the strong magnetic field, and impurity radiation is composed of line radiation and recombination emissions from impurities in the plasma. FAROES is a fusion systems code designed to perform optimization studies. Models for Bremsstrahlung, synchrotron, and impurity radiation in simple plasma geometries with triangularity are being incorporated into FAROES. Radiation models for flat, 'parabolic', and pedestal-type density and temperature profiles are being implemented. With these models, we study how radiation relates to overall systems cost, through the relationship between wall reflectivity and synchrotron losses, and through radiation due to impurities in the core. Constructing a radiation model in FAROES will allow for a more thorough account of the costs of fusion devices. |
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JP11.00219: Development of a 6-Axis Robot Arm for Precision ICF Component Manipulation Jonathan Sutherland, Kurt Boehm, Matthew Quinn, Eduardo Del Rio Small shells (1-2mm diameter) are used at the center of inertial confinement fusion experiments performed at laser facilities such as NIF and the Omega Laser at LLE. In addressing the demand for higher quality shells, General Atomics is developing instruments to measure a large variety of physical attributes of the shells it produces, e.g. surface morphology, out-of-roundness, surface defects, shell thickness and composition. Manual handling of the shells between inspections increases risks of damaging or contaminating the shells. Introducing automated shell handling reduces the risks of shell damage and contamination, decreases operator effort, improves efficiency and enables precise reorientation and positioning of the shells. For this purpose, General Atomics is evaluating a compact 6-axis robotic arm, the Mecademic Meca500. Equipped with the required tools and end-effectors, the precision of the Meca500 robot arm makes it a promising candidate to be used in performing automated shell handling operations without causing damage. Development of tooling, end effectors and the suite of tests needed to demonstrate the robot’s overall suitability for shell manipulation is the topic of this work. |
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JP11.00220: Enabling Optimized Divertor Design for Stellarators William Teague, Kenneth C Hammond, David A Gates In magnetic confinement fusion devices such as stellarators, the divertor is crucial for vessel protection and fuel exhaust removal. Even so, stellarator plasma optimization software to date has generally not included or accounted for divertor design. One approach to include the divertor in stellarator optimization is to incorporate an automated divertor design procedure that computes predetermined objective functions for compatibility and robustness. To address this, we develop a code that designs a rudimentary divertor according to the particle and heat exhaust patterns of a given plasma. This design process works by determining the location and optimal surface geometry for components using heat load predictions from diffusive field line tracing. These designs could then be used to inform optimization objectives within stellarator optimization codes and also serve as a basis for detailed engineering design. We present the latest progress in this code development and discuss potential formulations for optimization objectives. |
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JP11.00221: Fine Grid Adaptation to Study Dynamic Ion Wake Fields Abbie Terrell, Katrina Vermillion, Dustin L Sanford, Lorin S Matthews, Marlene Rosenberg, Peter Hartmann, Truell W Hyde Ion wake fields in complex plasma systems have been observed to cause non-reciprocal reactions between dust grains at sufficiently high ion drift velocities. Multiple experiments in the dusty plasma field, including the PK-4 experiment on the International Space Station (ISS), have provided evidence of these ion wake fields, but the changing dynamic effect of ion wakes as dust configurations evolve are not well understood. In order to understand particle behavior in complex plasma systems, a multi-scale Molecular Dynamics (MD) simulation, coupled with a 2D particle-in-cell with Monte Carlo Collisions (PIC/MCC) code, is used to examine the effects of ion wakes on dynamic dust systems. Here we discuss adaptations to this model to included heightened precision in ion-dense areas in order to study the combined potential of the dust and ions as the configuration of the dust changes. |
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JP11.00222: Using CRASH to analyze experimental setups in Kevin-Helmholtz experiments Benjamin H Thompson, Adrianna Angulo, Matthew Trantham, Shane X Coffing, Guy Malamud, Assaf Shimony, Carolyn C Kuranz Recent series of experimental shots explored the importance of the Kevin-Helmholtz instability in early galactic formation, specifically cold, dense streams feeding mass into a galaxy. The experiment basic setup was a laser-driven shock in low-density foam over a perturbed solid rod. However, subsequent experimental shots showed differences in shock speeds which required investigation. These results are explained by changes in diagnostics and laser drive. We used the radiation hydrodynamics code CRASH supplemented by Leeor one dimensional code simulations to explain the differences in shock speeds. These simulations provided a key role for analysis for how variations in experimental setup resulted in the shock speed differences. |
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JP11.00223: Prototyping EPICS Control Systems for Laser Laboratories Keily Valdez Sereno, Emiko Ito, Scott Feister Lasers for plasma science experiments traditionally needed extended cooldowns and were limited in how often they could fire. Now, many can fire several times per second! We need something to automate data collection in increasingly high-repetition-rate experiments. Rather than create our own tools, we turned to EPICS as a facility control system with a global research community. EPICS is already being used for complex facilities in high-energy physics and astronomy. Our goal was to explore the practicality of EPICS for all sizes of high-intensity-laser laboratory experiments. We built a small-scale prototype control system in EPICS using a network of Raspberry Pi computers, LEDs, and switches. Our completed documentation allows students and scientists to recreate the system. We took what we learned from the small system and applied it to real scientific equipment in a professional laser laboratory. We are undergraduate students who built our own distributed control system that can be scaled up for real-world laboratories. This will enable facility-wide automation to help high-intensity-laser laboratories run at high-repetition rates. |
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JP11.00224: Permanent Magnet Mirror Sreya Vangara, Steven C Cowley Advances in permanent magnet technology may enable their usage as a simple and accessible option for fusion mirror configurations. Permanent magnets do not require power supplies or cryogenic cooling, and are conveniently adjustable, demountable, and low-cost. Attaining high magnetic field strengths is challenging, though, since the maximum remanent magnetization of the evaluated neodymium boron iron permanent magnets (NdFeB) is 1.4 Tesla. However, by implementing a judicious configuration, we are able to demonstrate a magnetic mirror with field maxima of 5 Tesla. Producing magnetic fields exceeding this strength would begin to demagnetize the permanent magnets at room temperature. The configuration is built from analytic optimized solutions, which can be utilized to generate mirror devices with different geometries and parameters. Possible applications of the theoretical configurations range from plasma confinement in stellarators to medical imaging devices, and will be discussed during the presentation. |
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JP11.00225: The Target Chamber Manipulator Christopher J Ventre, Caroline Axelsen The Target Chamber Manipulator (TCM) system allows users to remotely control the angular positions of multiple detectors in the high vacuum 30R end station of the 1.7 MV tandem Pelletron accelerator. Previously, in order to accumulate data from a surface barrier detector at various angular and radial positions, the vacuum chamber was first filled with 1 atmosphere of dry nitrogen, then opened to atmosphere so that the detectors would be repositioned by hand. Evacuating the chamber required several more hours. The entire process took approximately 6 hours to complete, this added substantial time to those experiments requiring frequent repositioning of the detectors. To mitigate this problem and reduce vacuum failure risks from excessive cycling, a TCM system was designed and built at SUNY Geneseo. The system uses LabVIEW to control stepper motors to move the detectors in the chamber. Prior to the summer of 2021, jamming between the drive chain and the main sprocket occurred regularly, and excessive friction between the sprocket and chain occurred intermittingly, inhibiting motion. During the summer of 2021 the TCM was improved by increasing its efficiency and accuracy. The mechanical integrity of the TCM was enhanced by machining the sprocket to better tolerances and 3D printing an alignment tool, which allowed for consistent and reproducible angular alignment. While using a newly constructed electronics control system that simplifies interfacing from the TCM to the computer, time required to perform a Rutherford backscattering spectroscopy experiment will now be significantly reduced from multiple days to just a few hours. Funded in part by a grant from the DOE through the Laboratory for Laser Energetics. |
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JP11.00226: Installation of New High-Field Mirror Coil Magnets on the Big Red Ball Frank Wang, Ken Flanagan, Joseph R Olson, Cary B Forest A set of high-strength (0.3 T on-axis) coils have been installed on opposing ends of the BRB experiment; the coils serve to produce a large mirror within BRB. The mirror configuration can be varied by independently controlling the current through the existing Helmholtz coils and the mirror coils. The coils consist of 128 turns of internally water cooled copper conductor and have a bore of 14 inches with a 30.75 inch outside diameter. Plasma is produced with an array of washer guns mounted inside the coils. Future work will focus on spherical mirror stability in this configuration as well as the introduction of rotation using WiPPL LaB6 emissive cathodes to bias the magnetized plasma column. |
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JP11.00227: Analysis of intra-ELM tungsten erosion during partially-detached plasma operation in DIII-D Logan Webber, Gregory Sinclair, Tyler Abrams Tungsten (W) is a favorable material for plasma-facing divertor components due to properties such as a high melting point, thermal conductivity & low sputtering yield, which will be necessary to tolerate the extreme heat & particle flux faced by the divertor. Edge-Localized Modes (ELMs) are predicted to be a significant cause of erosion in both current and future fusion devices. A technique known as detachment may be used to reduce particle & heat flux reaching the divertor target during ELMs. Detachment involves increasing divertor density to lower the divertor plasma temperature. However, ELMs may “burn through” the detachment front, leading to detrimental levels of W-erosion. This research examines trends in intra-ELM W-erosion during detached operation by focusing on data collected from the DIII-D Metal Rings Campaign, which tested two rows of toroidally-symmetric, W-coated tiles in the lower divertor. The erosion rate was quantified via high-resolution WI emission spectroscopy and the degree of detachment via Langmuir probe & line-averaged density measurements. The authors intend for this work to guide development of partially-detached scenarios that are robust against ELMs, thereby reducing erosion & long-term damage to divertor PFCs. |
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JP11.00228: Measurements of the dust acoustic wave in a high magnetic field environment Jeremiah D Williams, Thomas Weis, Saikat Chakraborty Thakur, Stephen Williams, Edward E Thomas A dusty plasma is a traditional plasma system with a third charged species consisting of nanometer to micron sized particulate matter. The presence of this third charged species results in a system that is notably more complex than the traditional plasma system and supports a wide range of physical phenomena, including a wave mode known dust acoustic wave. Recent measurements of the properties of this wave have shown unexpected behavior and suggests that thermal effects are important in understanding the behavior of the dust. One proposed mechanism for the observed thermal effects is an ion-dust streaming instability. In this poster, we present preliminary results of an experimental study examining the properties of this wave mode in the Magnetized Dusty Plasma Experiment (MDPX) device at Auburn University, where it is possible to vary the strength and direction of the magnetic field relative to the direction of wave propagation and to control the direction of ion flow through the dust cloud. |
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JP11.00229: Simple Multi-physics analysis to understand quench behavior of HTS Magnets Erron Williams, Yuhu Zhai, aissata diop Due to the high Current and Magnetic Field demands required to maintain plasma confinement for fusion, Conventional Copper coils can only be operated for very brief pulse reactions before needing to enter a long cool-down period such as that in the National Spherical Torus Experiment(NSTX) and NSTX-Upgrade (NSTX-U) operation. High-Temperature Superconductors (HTS) are considered game-changing for long pulse or steady-state operation of compact fusion reactors as an enabling technology to access higher fields and longer pulse operations. HTS will run efficiently with no electrical resistance so long as they are operated under their critical current limits to avoid causing an issue known as quench. To better understand how to manage this quench and associated stress issue in superconducting magnets, COMSOL Multiphysics is used to develop a virtual engineering environment for finite element analysis of quench (thermal and mechanical behavior) in superconducting magnets along with Livelink to MATLAB. |
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JP11.00230: Modeling Nonidealities in a Coaxial Transmission Line for the DIII-D Helicon System Ethan M Williams, Robert I Pinsker, Michael W Brookman The helicon system at DIII-D can provide 1 MW of power at 476 MHz to the DIII-D tokamak from a single klystron source. The RF power is transmitted through ~100 m coaxial transmission line formerly used at lower frequencies (~60-120 MHz). In an ideal system all the generated power is transmitted to the tokamak, but due to nonidealities such as insulating supports for the center conductor, some level of wave reflections are inevitable. At frequencies below ~100 MHz, these reflections are negligible, but at the frequency (~0.5 GHz) for the helicon system, they can be significant. Modifications of the coaxial components were made to address this issue; subsequent measurements have shown acceptably low wave reflection at 476 MHz. To verify these findings, the transmission line nonidealities, focusing on 90-deg bends and insulating supports, are being studied with COMSOL Multiphysics. Simulations of these components are compared to experimental results and the effects due to the insulating supports are investigated. |
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JP11.00231: A Python Tool to Test for Stellarator Configuration Optimizations Wenxi Wu, Nastassia Patnaik, Nathaniel Stauffer, Santiago Lisa, William D Dorland, Tony Qian, Michael Zarnstoff, Braden Buck, Chesson Sipling, Brian X Jiang, Sorah Fischer Our project is based on Fuse0D: A Simple Spreadsheet-type Code Based on 0D Fusion Device Scalings, which was a model proposed in 2019 by Greg Hammett, Rob Goldston, and other scientists with the intention to better understand the relative performance of stellarators as various parameters are changing and various physics and engineering assumptions are constantly updating. Our code calculates values of estimated heating power, volume averaged density and helium concentration which would generate a maximum Q value and a minimum ISS-04 H confinement scaling. By inputting different testing parameter values onto our Python program, scientists can utilize this tool to test and calculate the desired geometry values conveniently and efficiently before actually building machines that could be expensive and deliver unsatisfying results. Additionally, we could demonstrate the use of our tool by studying the impact of aspect ratio on stellarator performance in the 0-D limit. |
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JP11.00232: Implementation of 3D blob tracking algorithm inside tokamak scrape-off layer David T Xiong, Rupak Mukherjee, Ammar Hakim One of the burning open problems of achieving fusion within a magnetically confined device is mitigating the megawatt scale plasma outflux on the divertor plates of a tokamak. A quite promising approach is to spread the extreme steady-state power/heat load on the divertor plates via plasma turbulence. Such turbulence in the scrape-off layer (SOL) is primarily mediated via toroidally elongated coherent density structures, called `plasma blobs'. These plasma blobs drift radially outward due to the magnetic field curvature effects. Efficient tracking of such blobs are necessary to understand and control the turbulence in the open-field-line region. However tracking becomes challenging as the shape and size of these blobs change as they propagate in the SOL [1]. We have developed a numerical tool for tracking such arbitrary shape-changing features/structures in 3D as they move. We `triangulate' the closed density isosurfaces and employ a 3D ray-tracing algorithm to discriminate between blobs and density holes. We use Gkeyll simulation data for tracking such blobs as test cases for simplified magnetic field geometry with realistic mass ratio. |
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JP11.00233: Driver optimization for a rotating magnetic field system Ao Zhang, Steven P Oliva, Jeremiah Kirch, Karsten J McCollam, Cary B Forest We measured amplifier characteristics and developed coil hardware for a rotating magnetic field (RMF) system to be tested on the Big Red Ball (BRB) device at the Wisconsin Plasma Physics Laboratory. Two orthogonal pairs of Helmholtz-like coils, which will be driven by quadrature-phased AC power supplies to produce a rotating dipole field, are to be constructed. The supplies use Class-C tube amplifiers, requiring less than 1 kW input for approximately 150 kW average power output per channel. Each channel's RMF coil will consist of 6 turns of 18 mm diameter litz wire, formed into a series pair. Our measurements have shown that the unloaded Q factor of this coil is larger than 100, permitting the necessary resonant current of 5kA in the coil given available power. However, the shape, size, and position of the coils are still in the process of optimization. The coils will be placed tightly and symmetrically in a dielectric pressure vessel at atmosphere inserted to the center of BRB, supported by a pedestal pipe. |
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JP11.00234: Analysis of MHD Modes in Predicting ELM Onset using Machine Learning Techniques Jeffrey Zimmerman, Ahmed Diallo, Christopher Battista Detection and prevention of edge localized modes (ELMs), which are destructive disturbances in the edge regions of H-mode toroidal plasmas, pose a significant roadblock to the development of stable, efficient fusion reactors. This problem is compounded by the fact that while models have been proposed to explain mechanisms behind them, ELMs are widely considered to be beyond the state-of-the-art predictive modeling, resulting in limited theoretical understanding of ELM onset to date. Machine learning (ML) has demonstrated effectiveness on other difficult plasma physics problems, such as predicting turbulent fluxes and estimating thermodynamic profiles from sensing data. Here we apply two machine learning models to predict ELM onset directly from Mirnov coil sensor data taken from a General Atomics DIII-D tokamak. The ML models support a prediction horizon long enough for realistic real-time ELM detection and mitigation. The models (multivariate polynomial regression and multilayer perceptron neural network) perform better than chance, with mean R2 values of 0.39 and 0.45, respectively. In addition, we extract analytical representations from the polynomial regression model, yielding relationships between ELM occurrence and the presence of resonance modes in the magnetic flux density of fusion reactors. |
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JP11.00235: Investigation of neoclassical transport in an axisymmetric tokamak using a Neural Network Desiree Garcia, Nathaniel M Ferraro, Priyanjana Sinha, Michael Churchill Toroidal geometry and non-uniform magnetic fields give rise to a class of heat and particle transport known as "neoclassical transport." Neoclassical transport can play an important role in magnetic fusion devices, especially in the presence of non-axisymmetric fields or in regions where turbulence is suppressed, where it can become a dominant mechanism for heat and particle loss in the plasma. Several codes exist that can calculate neoclassical transport, including NEO. Although these codes are relatively efficient, they are too slow to be used effectively inside optimization loops, for real-time control, or within large-scale fluid models, especially when multiple ion species are present or in non-axisymmetric magnetic fields. This project seeks to develop a fast method for evaluating neoclassical transport using machine learning, by training a neural network using the output of NEO calculations. This neural network will be able to accelerate neoclassical transport modeling. Initial results are calculated using a single ion species in axisymmetric Miller geometry. This work can be extended in the future to consider multiple ion species and non-axisymmetric geometries. |
Not Participating |
JP11.00236: Critical Gradient Computation with Respect To Stellarator Geometry Brian X Jiang, Mike Zarnstorff, William D Dorland, Tony Qian, Chesson Sipling, Braden Buck, Sorah Fischer, Nastassia Patnaik, Nathaniel Stauffer, Santiago Lisa, Wenxi Wu Surpassing the critical ion temperature gradient of a stellarator results in the onset of ion-temperature-gradient turbulent transport. Calculating this temperature gradient is important for modelling stellarator transport and temperature profiles. To this end, analytical and numerical methods for analyzing the growth of modes with respect to stellarator geometry are presented and evaluated. A description of the magnetic field and stellarator geometry is computed by VMEC, a magnetohydrodynamic optimizer, and GIST, which calculates drifts from curvature and shear, respectively. The stability of turbulence in the resulting simulation is analyzed by either solving an eigenvalue stability problem [1] or applying the GX gyrofluid turbulence simulation code. The efficiency and accuracy of these methods are discussed. |
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JP11.00237: Consideration of Vacuum Vessel Properties Required for PFRC-type Fusion Reactors Miles J Kim, Samuel A Cohen The fourth Princeton Reversed Field Configuration (PFRC-4) is a device designed to produce net power output through the fusion of deuterium and helium-3. Its inner walls would be bathed by 2.45 MeV neutrons as well as synchrotron and Bremsstrahlung radiation. The PFRC-4 device’s vacuum vessel must serve several purposes including: shielding its magnets and any nearby human operators from neutron radiation; extracting useful energy from the incident radiation; and providing compatibility with RF heating. To find a suitable wall material, we report on nuclear, thermal, electrical, optical, and mechanical properties and fabrication techniques for the vessel. Neutron shielding, combined with weight and thickness requirements, strongly support the use of pure B-10 and its light compounds, e.g., boron carbide, and boron nitride. The variability of these properties with temperature and prolonged neutron exposure is described. We identify data not currently available for the materials considered. The dimensions of the vessel, the design of the cooling channels and how their geometry will affect thermal gradients and stresses in the vessel, and methods of manufacturing and assembling the vessel are also discussed. A multi-layer wall which separates the required functions is described. |
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JP11.00238: Self-regulation of particle acceleration in quasi-parallel shocks in MHD-PIC simulations Alisa Galishnikova, Anatoly Spitkovsky Shock waves in supernova remnants are known to produce non-thermal particles, cosmic rays, via the first order Fermi acceleration mechanism. The most self-consistent way to study this process is to solve kinetic equations using particle-in-cell methods, which are computationally expensive due to the need to resolve microscopic plasma scales. In this work, we study electron acceleration in quasi-parallel shocks using a hybrid code which treats cosmic ray electrons (CRe) as particles, while the thermal electron-ion plasma is described as a fluid by magnetohydrodynamic equations. This MHD-PIC method captures the microphysics of CRe and includes their momentum and energy feedback in the fluid equations. We study the acceleration and feedback mechanisms of CRe on macroscopic scales during the long-term evolution of the system. Instead of utilizing constant injection parameters, we implement injection prescriptions based on a self-consistent reflectivity of the shock which we determine by tracing test particles through MHD turbulence. This approach allows us to study the long-term evolution of the upstream turbulence and the particle acceleration process. We show how the injection efficiency of quasi-parallel shocks is self-regulated by accelerated particles. |
Not Participating |
JP11.00239: Analysis of Opaque X-ray Lineshapes from Hot Dense Plasma Paulette C Albino Castillo, Phil Efthimion, Brian F Kraus, Lan Gao, M Bitter, Kenneth Hill, Adam F Moreau, Reed C Hollinger, Shoujun Wang, Huanyu Song, Jorge J Rocca Irradiating solid targets with high intensity lasers creates some of the densest and brightest laboratory plasmas which are often used as a source of relativistic particles and x-rays. This analysis examines a collection of x-ray spectra from the ALEPH 400 nm laser facility at Colorado State University, obtained with a high-resolution Bragg crystal spectrometer. The laser deposited 8-10 J in 45 fs pulses, with an intensity of ∽3x10 22 W/cm2, focused onto multilayer targets composed of Al and Ti of varying thicknesses. Titanium plasma becomes highly ionized under these conditions, emitting photons through the resonance transition 1s2p → 1s2 that are energetic enough to escape the dense plasma, but which are susceptible to opacity effects. Resonance line widths were measured and fit to modeled lineshapes in order to gauge the presence and degree of self-reversal, which varies with optical depth and thus Ti layer thickness. Measuring opacity effects for different target parameters can constrain plasma conditions and aid in the understanding of radiation transport within these high temperature, solid-density plasmas. |
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JP11.00240: Reconnection Simulations for the affirmation of synchrotron induced photon distribution changes Emmanuel Aneke, Hayk Hakobyan, Alexander A Philippov Pulsars are essentially magnetized spinning neutron stars that emit radiation out of its magnetic poles. They are one of the potential remnants of a supernova. Magnetic reconnection is an astrophysical phenomenon where the colliding magnetic fields accelerate a beam of particles and produce radiation. Inherently, our knowledge on reconnection is limited because all we observe are the pulses of light form them. Using macroparticle with particle in cell codes driven by supercomputers, we simulate the reconnection process. Synchrotron radiation is light emitted by relativistic charged particles experiencing a magnetic field. This is impossible to avoid in reconnection and must be taken into account. The synchrotron radiation emitted by the reconnection particles causes them to lose some of their energy by a method called synchrotron radiation cooling. By performing simulations of reconnection with various synchrotron radiation cooling parameters, different particle distributions can be generated. From then, the particle distributions can be compared to observed photon distribution data from real pulsars. This poster discusses the accuracy of macroparticle simulations of local and global reconnection. In turn, implications of integrating synchrotron radiation cooling into the reconnection simulations and how the observed photon distributions can be found analogous to the simulated values are also discussed. |
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JP11.00241: Loss Particle Trajectories in Quasi-Axisymmetric Stellarators Matt Landreman, Landry Horimbere, Daniel Alex Stellarators are a class of plasma device designed to achieve nuclear fusion using magnetic confinement. The magnetic field must confine high energy alpha particles, a byproduct of a Deuterium-Tritium fusion reaction. Work involved the simulation of alpha particle confinement in Beams3d for multiple quasi-axisymmetric stellarator fields to analyze particle loss trajectories. MATLAB algorithms were developed to isolate and classify particle trajectories to examine disparities in performance between fields optimized for quasi-symmetry. Fields with multiple flux surfaces optimized for quasi-symmetry had the lowest particle loss fractions. Future work must focus on the development of improved objective functions for particle confinement. |
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JP11.00242: Probing the PMI Properties of Tungsten-based High-entropy Alloys as Plasma-facing Components Muhammad A Abdelghany, Meral Sharkass, Ming Kit Cheng, Jean Paul Allain High-entropy alloys (HEAs) are a novel class of complex materials that contain several principal elements in equal or near-equal atomic percent. W-based HEAs exhibit high structure stability under irradiation and outstanding mechanical properties at elevated temperatures. However, we still don’t fully understand the synergistic radiation and plasma interactions with this new class of material and how their properties change under extreme conditions. Our objective in this project is to probe the feasibility of understanding and predicting how irradiation-driven composition of W-based HEA affects its PMI properties, especially surface evolution. In this work, we adopted an energy landscape modeling technique to develop a Deep Neural Network that incorporates the potential energy functions of a W-HEA composed of WTaCrV. Machine learning was employed to use the deep potential MD scheme to perform MD modeling that has the same accuracy as the first-principle models. This approach was validated and compared with results from using EAM potentials. To capture the ion-induced mixing, BCA calculations of N and Ar irradiation were performed using DYNAMIX. Irradiation experiments of N and Ar with fluences of [1015-1017] cm-2, 45° incidence, and 1 KeV were also performed in IGNIS-I at UIUC. |
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JP11.00243: ExASIM: Robust Platform for Modeling Plasma Material Interactions Meral Sharkass, Muhammad A Abdelghany, Jean Paul Allain ExASIM is a framework that provides a computational conjunction of atomistic simulations with advanced MD and multi-component BCA calculations to handle complex reactive and geometric systems efficiently. It is used to study W-based complex alloys under conditions relevant to fusion plasma-materials interactions (PMI). It allows for more accurate simulations by prioritizing simulation techniques in appropriate energy, spatial and temporal physical regimes according to the PMI conditions studied. ExASIM generates surfaces with specific properties (Porosities, crystal structures, and grains). Then, it reduces surfaces to simple components such as: grain boundaries and materials interfaces. Modeling simple components is performed by fast BCA simulations using DYNAMIX. While for non-uniform components, complex interfaces, and low energy ion irradiation, LAMMPS is used for atomistic simulations. Simulations are iterated to determine self-interactions and at the final stage, results of the individual components from LAMMPS and DYNAMIX are coupled to reconstruct the resulting total surface. This platform is used to model irradiation of N and Ar beams with fluence of 1017 cm-2 incident on pure and porous W at 500 eV and 1 keV at 0o, 45o and 70o angles of incidence. |
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