Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session TP11: Poster Session VII: In-Person, Hall A (9:30-11:00am) and Virtual Poster Presentations (11:15am-12:30pm)
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Room: Exhibit Hall A and Online |
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TP11.00001: MFE: FRC, RFPS etc Session Chairs: |
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TP11.00002: Electrical modeling and scaling of the HelicitySpace peristaltic compressor Seth Pree, Natalija Marin, Setthivoine You, Carlos A Romero-Talamás, Paul M Bellan The Helicity Drive concept introduced in [1] and being developed by the HelicitySpace LLC will utilize a peristaltic magnetic compressor [2] to compress merged Taylor-State plasmas toward fusion conditions. The compression is predicted to occur as the plasma propagates along the bore of a linear array of Bitter coils arranged as a spatially varying, lumped-parameter transmission line driven by two capacitor banks discharged in succession. Circuit and magnetic field simulations have been developed and used to guide the design of a prototype compressor which has been built and tested at UMBC [3]. The timing and dispersion of the propagating magnetic field predicted by the simulations have been demonstrated in the prototype. The circuit simulations have been improved to calculate losses and complications which may occur when the compressor is placed in vacuum and used to transport and compress an actual plasma. Predictions of the plasma response to and back-reaction on the imploding field of the compressor will also be presented. |
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TP11.00003: Current status of the ECLAIR magneto-inertial fusion concept exploration experiment. Joseph I Samaniego, Setthivoine You, Paul M Bellan, Seth Pree, Carlos A Romero-Talamás, Natalija Marin, Michael R Brown, Shengtai Li, Hui Li ECLAIR is a new experiment under construction designed to investigate the Helicity Drive magneto-inertial fusion concept [1]. Helicity Drive operates in four sequential steps: (a) formation of multiple magnetized plectonemic Taylor states; (b) merging of the Taylor states into a single magnetized plasma jet heated via magnetic reconnection; (c) peristaltic compression of the merged jet to fusion conditions; (d) peristaltic expansion of the burning plasma to produce thrust and electrical power. We are now constructing 4 custom triple electrode plasma guns adapted from the precursor MOCHI experiment design [2]. The guns aim towards one focal point to promote reconnection-heating of the 4 plectonemes [3] at the inlet of the peristaltic magnetic nozzle. The magnetic nozzle consists of 20 Bitter-type coils connected in a transmission line setup [4] to peristaltically compress the preheated plasma. First plasma is expected end of 2022. |
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TP11.00004: Testing of the HelicitySpace Magnetic Field Compression Scheme. Natalija Marin Experimental results for a novel fusion propulsion concept proposed by HelicitySpace in collaboration with the Caltech and UMBC research teams are presented. The Helicity Drive is a novel magneto-inertial fusion propulsion concept for deep space travel [1]. The experiments were conducted at UMBC without plasma, closely matching theoretical predictions [2]. The experimental parameters were determined with a simulated peristaltic compressor [3], which is meant to adiabatically compress plasma preheated by magnetic reconnection. The nozzle consists of twenty Bitter-type magnets arranged as a transmission line, intended to compress merging plasma jets by forming a double-peaked traveling pulse. The pulses are initiated by an SCR trigger circuit which discharges a capacitor bank into the transmission line. Measurements of the time-varying, peristaltic magnetic field were performed with a B-dot probe, numerically integrated, and compared to theoretical and simulated predictions. |
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TP11.00005: Review of plasmoid reconnection and ion heating in the CHI experiments on Helicity Injected Spherical Torus (HIST) Masayoshi Nagata, Hideaki Miyamoto, Naoyuki Fukumoto, Takashi Kanki The key role of plasmoid-mediated magnetic reconnection was experimentally investigated during transient-Coaxial Helicity Injection (T-CHI) for non-inductive plasma start-up in the HIST device. The fast magnetic reconnection is required for the flux closure and ion heating at once in T-CHI discharges. Here, we will review them as follows; (a) In the ejection of plasma flow from the magnetized coaxial plasma gun during the helicity injection phase, a narrow current sheet is elongated and broken apart at some points inside it due to a tearing instability, so that three or four small-size plasmoids are born in sequence. The separation and coalescence of the multiple plasmoids are repeated through the reconnection, leading to a bigger plasmoid, namely closed flux surfaces. We observed the phenomena as magnetic field oscillations, which was newly named as the plasmoid oscillation. (b) Doppler ion temperature increased from ~10 eV up to 80 eV during the plasmoid oscillation. The ion heating driven by the regular reconnection during the repeated plasmoid merging has been for the first time identified on HIST. |
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TP11.00006: Modification of the RELAX for producing tokamaks as well as RFPs for investigating two-fluid toroidal plasmas Takeru Inoue, Haruhiko Himura, Akio Sanpei, Shinichiro Inagaki, Natsuki Kojima, Ryota Takaoka, Takahiro Sasaki, Mitsutaka Isobe, Abdulgader F Almagri The RFP machine "RELAX" has been upgraded to produce tokamak plasmas as well as RFPs to study the validity of two-fluid descriptions for those toroidal plasmas in low density regimes. For this purpose, the strength of the toroidal magnetic field (Bt) in the RELAX was planned to increase up to approximately 0.2 T, which would be about four times larger than that of RFPs. In the case, stronger electromagnetic (EM) forces obviously act on the set of toroidal field coils (TFCs). To mechanically support the TFCs during the tokamak formation, a complete set of three-dimensional EM forces and stresses were calculated by use of a finite element analysis method. According to those results, TFCs were completely fixed and tested in experiments. Regarding the discharge circuit supplying the current flowing into the TFCs, it achieved approximately 21 kA, which corresponds to Bt = 0.2 T. Currently, the first tokamak will be planned in the RELAX. This comparative study would help understanding the two-fluid description of the plasmas with relatively lower density where the ion skin depth is hardly short compared to the plasma size. |
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TP11.00007: Progress towards a high voltage, independently triggered, modular-coil Field Reversed Configuration experiment John C Boguski, Ian A Bean, Thomas E Weber Field-Reversed Configuration (FRC) plasmoids are ideal candidates for Magnetized Target Fusion (MTF) concepts, which rely on generating high density, translatable plasmas with sufficient lifetime to undergo compression. A new Field-Reversed Configuration (FRC) experiment is being constructed at Los Alamos National Laboratory capable of exploring high-density FRC formation with fast (sub-microsecond) reversal times and large inductive electric field (0.7 kV/cm) using new high voltage (80 kV), low inductance (100s nH), modular-coil hardware. Initial FRC formation results using the new hardware will be presented and performance limits of current techniques discussed. |
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TP11.00008: X-ray measurements of electron density and temperature in the PFRC-2 Christopher A Galea, Sangeeta P Vinoth, Stephanie J Thomas, Samuel A Cohen The Princeton Field-Reversed Configuration-2 (PFRC-2) is an FRC heating and confinement experiment. FRC plasmas are formed and heated by odd-parity rotating magnetic fields (RMFo). X-rays emitted via Bremsstrahlung from PFRC-2 plasma are of interest in order to measure electron energy distribution functions (EEDFs) from which electron number density ne and temperature Te can be extracted. Three Silicon Drift Detector (SDD) x-ray pulse-height detectors in the center cell measure the Bremsstrahlung emissions above 150 eV from three viewing chords, where two are near the central plane and the third is near the nozzle. We describe x-ray measurements of the PFRC-2 experiment both in the case where RMF is applied, resulting in an FRC, and in the case where RMF is not applied, which results in a quasi-Maxwellian tenuous plasma (ne < 109/cc) with effective temperatures reaching 1500 eV. For the FRC plasma, x-ray measurements have been conducted at 4.3 MHz RMF frequency, 70 - 100 kW RMF power, and 300 G vacuum field. Machine updates are in progress to lower RMF frequency to 2 MHz and increase magnetic field to 800 G in order to directly heat ions using RMFo. X-ray measurements for this new regime will also be discussed. |
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TP11.00009: The Balmer-line-ratio method to predict electron temperature using Collisional Radiative model for Hydrogen plasma in PFRC-II Sangeeta P Vinoth, Eugene S Evans, Eric Palmerduca, Samuel A Cohen A collisional-radiative (CR) model [1-4] to extract the electron temperature of hydrogen plasmas from Balmer-line ratio measurements has been developed. The forward component of the model computes the densities of excited states (up to n=15) as a function of electron temperature , electron density and the molecular-to-atomic neutral ratio . The backward component of the model uses interpolation to obtain electron temperature as a function of Balmer ratio, electron density , and the molecular-to-atomic neutral ratio . This CR model could yield time resolved predictions in the range 1-500 eV for hydrogen plasmas with up to cc and specified densities of molecular and atomic hydrogen neutrals. A comparison of different methods for determining the counts in a spectral line to calculate the Balmer line ratio and inferring the electron temperature is presented. The most trusted method in inferring the electron temperature is also discussed. |
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TP11.00010: An analytical approach to evaluate magnetic field closure and topological changes in FRC devices. Taosif Ahsan, Samuel A Cohen We describe mathematical methods, one based on analyzing the topology of modified non-linear flux function (MFF), |
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TP11.00011: Progress and Plans of C-2W Advanced Beam-Driven Field-Reversed Configuration Experiments Hiroshi Gota, Artem Smirnov, Michl Binderbauer, Deepak Gupta, Sergei Putvinski, Thomas Roche, Erik Trask, Peter Yushmanov, The TAE Team TAE Technologies, Inc. (TAE) is pursuing an alternative approach to magnetic confinement fusion, which relies on field-reversed configuration (FRC) plasmas composed of mostly energetic and well-confined particles. The high-energy particle population is produced by a state-of-the-art tunable energy neutral-beam (NB) injector system. TAE’s current experimental device, C-2W (a.k.a. Norman) [1], is the world’s largest compact-toroid device. It has made significant progress in FRC performance, producing record breaking, high temperature (Te >500 eV, Ttot >5 keV) advanced beam-driven FRC plasmas, dominated by injected fast particles and sustained in steady-state for up to 30 ms (limited only by the energy storage on-site). An active plasma control system has been developed and utilized in C-2W to produce better and consistent FRC performance using magnets, electrodes, gas injection, and tunable NBs. Overall FRC performance is well correlated with NBs and edge-biasing system, where higher total plasma energy is obtained by increasing both NB injection power and applied-voltage on biasing electrodes. This paper will review the highlights of recent C-2W experimental campaigns as well as future plans. |
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TP11.00012: Helicon waves in FRC configurations Francesco Ceccherini, Laura Galeotti, Sean Dettrick, Kevin Hubbard, Daniel C Barnes, TAE Team RF_Pisa is a full wave code that has previously been used to model HHFW in the LAPD device, as well as ICRH, ECH, mode conversion and minority ion heating in FRC geometry [1,2]. Recently, it has been extended to model the so-called Helicon regime. Waves in this regime are whistler-type waves with a two-branch dispersion relation and characteristic frequencies higher than the Lower Hybrid frequency. The two types of waves, referred to as Trivelpiece-Gould and Helicon, can access specific plasma density values only and transfer energy to the plasma through Landau and collisional dampings. Here through RF_Pisa simulations we first review and discuss the dispersion relation of the Helicon waves beyond the well-known limit cases that can be recovered analytically and then we present a series of results obtained for different plasma and antenna scenarios. Quantities of interest that shall be discussed include wave-plasma coupling, energy and momentum deposition, mode impedance as well as resistance spectra and resonances. Full 3D reconstructions for multi-phase antenna configurations shall be presented. |
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TP11.00013: Simulation of Neutral and Ion Sources and Sinks in Steady State C-2W Plasmas Sean Dettrick, Erik Granstedt, Martin Griswold, Erik Trask On the C-2W experiment it is possible to maintain Field Reversed Configuration (FRC) plasmas in steady state for tens of milliseconds [1]. The main energy and momentum source terms are provided by neutral beam injection and electrode biasing and the main particle source term is neutral gas injection. The sink terms, which balance these sources in steady state, include charge exchange losses of the fast ions, parallel losses to the divertor, and wall contact. To study the interplay between these sources and sinks, kinetic simulations of neutral and ion transport during neutral beam injection and gas fueling have been performed using a particle transport model where atomic and molecular ions and neutrals co-evolve, with each species acting as the target background for Monte Carlo Collisions with the other species. In this study we compare the particle fueling rate required to maintain constant inventory in different C-2W fueling configurations. |
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TP11.00014: Towards a Direct Internal Magnetic Field Measurement of a Translating Field-Reversed Configuration Plasma on C-2W Anton S Bondarenko, Juan Aviles, Kevin Phung, Jesus A Romero, Andrey Korepanov, TAE Team In TAE Technologies' current experimental device, C-2W (also called ”Norman’’) [1], record breaking, advanced beam-driven field reversed configuration (FRC) plasmas are produced and sustained in steady state utilizing variable energy neutral beams (15 - 40 keV, total power up to 20 MW), expander divertors, end bias electrodes, and an active plasma control system. Direct measurements of the FRC magnetic field topology are useful for validation of theoretical models and simulations but present an experimental challenge, as diagnostic probes generally disrupt plasma performance and suffer damage in the energetic core. In an effort to measure the internal magnetic field with minimal degradation of both probe and plasma, a novel experiment has been developed in which the programmable C-2W magnet system is utilized to rapidly translate an FRC past a custom insertable B-dot array. The array measures the axial and radial components of the magnetic field at four simultaneous locations along a radial axis and can be inserted via a motorized actuator to any position from the vessel wall to within the FRC null radius. In situ corrections for small rotational misalignments in the B-dot windings are achieved via calibration against a vacuum field eddy current model. In a preliminary deployment, the probe detects deformation in the poloidal field structure of the scrape-off layer that is consistent with a simple equilibrium FRC model. Diagnostic and experimental considerations for probe survivability, acquisition electronics protection, and future direct measurement of field reversal inside the null radius are addressed. |
Author not Attending |
TP11.00015: Non-singular computation of magnetic field created by 3D distributed plasma current density Sergei A Galkin, Jesus A Romero Computation of 3D magnetic field inside and nearby of 3D current carrying plasma is presented. Non-singular, accurate and “fast” (a few seconds on laptop with moderate dense 3D grid) method, based on numerical solution to a few 3D Poisson’s equations, is used. The 3D magnetic solver “ELSOME” was developed and aligned with plasma and vessel geometry and parameters typical for plasma shots in the C-2W device [1]. Although FRC plasmas and currents are mainly designed to be axisymmetric, some physics models naturally bring 3D effects. Any unstable mode with mode number greater than 0 produces 3D current perturbation, which can be transformed into 3D magnetic field (MF) perturbation with help of ELSOME. Non-axisymmetric fast ion current, due to the finite number of neutral beams on each injection plane, generates 3D MF perturbations, which can be computed by ELSOME too. We will discuss possible implementations of ELSOME to improve plasma operations, including some 3D diagnostic effects also. Details of the 3D magnetic model and the solver will be presented too. |
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TP11.00016: Generation of Terahertz Radiation from Laser Irradiation of Wires to Enable Internal Magnetic Field Measurement in Burning Plasmas via Pulsed Polarimetry ALES NECAS, Roger J Smith, Kan Zhai, Gerrit Bruhaug Advanced Bayesian Analysis and interpretive physics modeling of the C-2W beam-driven Field-Reversed Configuration (FRC) experiment provide ample indirect evidence of magnetic field reversal [1]. However, a direct measurement of the magnetic field reversal in an FRC is an extremely challenging task. |
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TP11.00017: Measurement of End Losses from C-2W's Open Field line Plasma Martin Griswold, The TAE Team In TAE Technologies’ current experimental device, C-2W (also called “Norman”) [1], the FRC core plasma is surrounded by a mirror-confined scrape-off layer on open field lines. These open field lines expand by a factor of ~30 in the divertors before terminating on a set of concentric electrodes that are used for plasma biasing. An array of energy analyzers and bolometers mounted on the divertor electrodes [2] measures axial power losses as well as the electron temperature and ion energy distribution function (IEDF) of the plasma at the termination point of the open field lines. We use this system to study the sheath and pre-sheath voltage drops that form in the expanding magnetic field divertors at various levels of electrode bias. We show that a "clean divertor" ambipolar potential of (~4.5 Te) forms to limit electron parallel transport whether or not the biasing system is active. |
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TP11.00018: Monitoring Impurities and Hydrogen Isotopes using Survey Spectroscopy in C-2W Yasmeen Musthafa, Marcel Nations, James Sweeney, Dima Osin, Deepak Gupta In TAE Technologies’ current experimental device C-2W (also known as “Norman”), steady-state beam-driven field reversed configuration (FRC) plasmas are produced and monitored with an extensive suite of plasma diagnostics [1]. In order to investigate impurity and hydrogen isotope composition in C-2W, an array of survey spectrometers was deployed to measure the spectral distribution of lines from the ultraviolet to the near-infrared in different regions of the device on a shot-to-shot basis. Spectral analysis using sophisticated line identification methods offers a comprehensive picture of the plasma composition as a function of machine configuration and operating conditions. The measured spectra can provide a significant amount of useful information, including insight into wall conditions following machine vents, electrode arcing events, metal sputtering by fast particles, and leak detection. In addition, some systems can resolve hydrogen and deuterium Balmer-alpha lines for studies of particle confinement, gas fueling, and wall recycling. In this poster, we will summarize C-2W’s survey spectroscopy capabilities and present data exploring impurity trends, hydrogen isotope confinement, and various other phenomena in C-2W. |
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TP11.00019: Microwave to THz diagnostic opportunities on FRC plasmas of TAE's Norm and Copernicus devices Roger J Smith, Eli Parke, Michael Beall, Chuanbao Deng, Laura Galeotti, Kan Zhai The field reversed configuration (FRC) is a high beta poloidal field equilibrium with presumably negligible toroidal field. The FRC equilibrium concept being pursued at TAE Technologies has a significant neutral beam injected (NBI) fast ion component and plasma, extended outside the separatrix, connected to biasing electrodes lying outside the confining mirror regions. These FRC equilibria offer unique instrumental challenges to optical diagnostics that seek to provide density and magnetic field profile details. A study of the utility of interferometry, polarimetry and reflectometry diagnostics to the present Norm device and extrapolation to the future Copernicus device is presented. The parameter range of density and magnetic fields require probing wavelengths in the 100 micron to cm range. Conventional diagnostic systems and lesser known Pulsed Polarimeter and Radial Interferometer Polarimeter (RIP) diagnostics will be discussed for their utility in determining internal equilibrium distributions of ne and B and providing measurements of fluctuation activity in ne and B, such as identifying the internal tilt instability. Measured density distributions on Norm and simulated equilibrium data on Copernicus are used. |
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TP11.00020: Helium jet spectroscopy in the divertor region of C-2W Marcel Nations, Erik Granstedt, Dima Osin, Deepak Gupta, Kurt Knapp, the TAE team TAE Technologies’ current experimental device, C-2W (also called “Norman”), is an advanced, neutral beam-driven, field-reversed configuration (FRC), which utilizes edge control by means of electrode biasing to stabilize the FRC. [1] Applied potentials at the boundary generate radial electric fields which affect plasma rotation in open field lines due to azimuthal ExB drift. A recently deployed supersonic helium gas injector provides target impurities and a promising opportunity for spectroscopic measurements in the divertor region of C-2W. A high-resolution spectrometer was utilized to measure the Doppler shift of target helium transitions and infer radial electric fields from the temporal evolution of azimuthal velocities. These measurements can help validate axial electrostatic potential and circuit models under development at TAE. Experimental design details and diagnostic capabilities will be presented and discussed.
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TP11.00021: Density Fluctuation Measurements in C-2W FRC Plasmas Eli Parke, Michael Beall, Chuanbao Deng, Roger J Smith, James Titus, Kan Zhai, the TAE Team In TAE Technologies’ current experimental device, C-2W (also called “Norman”) [1], record breaking, advanced beam-driven field reversed configuration (FRC) plasmas are produced and sustained in steady state utilizing variable energy neutral beams, advanced divertors, end bias electrodes, and an active plasma control system. Line-integrated electron density measurements from the multi-chord far-infrared (FIR) interferometer system provide high resolution, high bandwidth fluctuation measurements that can be used to probe the interactions of injected energetic particles with the FRC. Beam-induced instabilities like micro-bursts have been observed at frequencies above those observed for rotational instabilities (typically a few tens of kHz) [2]. For mode activity found above 100 kHz, measurements of the spatial structure and location of the instabilities are presented for different plasma conditions. |
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TP11.00022: The Optimization of the C-2W Experimental Device for Energetic, Long-Lived Plasma Thomas Roche, Hiroshi Gota, Erik Trask, E A Baltz, The TAE Team The experimental device C-2W [1], also known as Norman, was initially optimized in early 2019 to performance levels up to and exceeding its specified design points. Plasma durations on the order of 100s of Alfven times (????) coinciding with the energy storage capabilities of the facility (30 ???? duration) and total plasma temperatures in excess of 1000 ???? represent a minimal expression of these design points. Through an iterative series of optimization of formation / target generation, magnetic field topology shaping, neutral beam power, edge biasing, and gas fueling this goal was realized. Google's optometrist algorithm was integral to this process [2]. Here we describe some of the processes involved in these optimizations and how they have led to greater insight about FRC plasmas and the most high-performance FRCs ever generated. |
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TP11.00023: Z-effective measurements using visible Bremsstrahlung radiation during impurity injection experiments in C-2W James Sweeney, Marcel Nations, TAE Team The C-2W fusion experiment [1] at TAE Technologies is an advanced experimental device for creating field-reversed configuration (FRC) plasmas. The FRCs are produced using neutral beam injection, edge biasing, and fueling with hydrogen pellets, compact-toroids, and neutral gas. The plasma also contains impurities, and to enhance understanding of impurity transport in C-2W a study was conducted in which gas impurities were edge-injected. An optical mount collected line-integrated emission from 15 chords along a radial plane through the plasma center. For each view a photomultiplier tube and narrow bandpass filter (~523nm) sampled the visible background Bremsstrahlung radiation. [2] These line integrated measurements were inverted into local profiles and utilized with electron temperature and density from Thomson scattering and far-infrared interferometry to provide time-resolved radial Z-effective profiles. Injection of impurities of higher Z at the plasma edge resulted in an increase in Z-effective at the plasma core, suggesting both parallel transport along the FRC scrape-off-layer and radial transport through the FRC separatrix. |
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TP11.00024: C-2W FRC plasma Te and ne profiles comparison under different machine configurations Kan Zhai, Kan Zhai, Eli Parke, Michael Beall, Christina Stonier, John Kinley, Angelica Ottaviano, the TAE Team C-2W is an advanced beam driven Field Reversed Configuration (FRC) fusion device, in which plasma sustainment with total temperature above 5 keV has been demonstrated [1]. In order to better understand the machine performance and to prepare for the design of TAE’s next generation experiment device, called Copernicus, a series of experiments with different field configuration and fueling schemes have been carried out on C-2W. In summary we have studied plasma behavior in three mirror field configurations with no mirror plug, external mirror plug, and internal mirror plug. In parallel with these field configuration experiments, we have also studied different fueling schemes in which gas fueling is introduced from different locations and from the additionally installed gas section with moveable fueling pipe. The corresponding plasma behavior of electron temperature and density profile measured in these experiments will be reported. |
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TP11.00025: 2-D Electron Density Profiles Using Inverse Radon Transformation in C2W Field Reverse Configuration Chuanbao Deng, M. Beall, E. Parke, R. Smith, C. Stonier, K. Zhai, TAE Team In the TAE Technologies current experimental device, C-2W (also called “Norman”) [1], record breaking, advanced beam-driven, high temperature field reversed configuration (FRC) plasmas are produced and sustained in steady state utilizing variable energy neutral beams, advanced divertors, end bias electrodes, and an active plasma control system. The density equilibrium profiles and fluctuations are measured with the powerful 14 chords FIR interferometer system [2]. An inverse Radon transformation algorithm has been developed to calculate the 2-D density profile structures at mid-plane from the multi-channel FIR interferometer measurement. The variation of electron density profiles in different plasmas and configurations are observed, which may indicate the changes in particle confinement. |
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TP11.00026: Magnetic Field-Shaping Effects on Tilt Stability in C-2W Field Reversed Configuration Timothy A DeHaas TAE Technologies’ current experimental device, C-2W (also called “Norman”), is an advanced, neutral beam-driven, field-reversed configuration (FRC). [1] Traditional FRCs are known to be theoretically unstable to an internal tilt mode whose threshold is characterized by the parameter S*/E. Here, S* is the FRC radius divided by the ion inertial length, and E is the FRC elongation. [2] Experimental evidence from previous FRC devices has suggested that the threshold for the tilt is S*/E ~ 3. C-2W has demonstrated higher S*/E than this prior empirical limit due to a large population of fast ions from neutral beam injection. Understanding this link between the two will be crucial for any future FRC device. A series of experiments was conducted to change the shape of the FRC and the distribution of fast ions therein by utilizing the field-shaping modularity from fast, external magnetic coils. FRC was found to be stable to the tilt mode for the entire range of mapped space in S* and Elongation. By concentrating the fast ions near the midplane of the device, S* was pushed to its highest levels recorded in C-2W, while lengthening the FRC helps stabilize fast ion-driven modes. |
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TP11.00027: Equilibrium Reconstruction of Beam Driven C-2W Plasmas Sean Dettrick, Sangeeta Gupta, Isabelle Sato, Kevin Hubbard, Peter Yushmanov In TAE Technologies' current experimental device, C-2W (also called ``Norm'') [1], record-breaking, advanced beam-driven field reversed configuration (FRC) plasmas are produced and sustained in steady-state utilizing variable energy neutral beams, advanced divertors, end bias electrodes, and an active plasma control system. An axisymmetric 2-D interpretative equilibrium code with Kinetic fast ions is developed to infer the internal magnetic field configuration from experimental measurement including the radial profile of density and temperature at the midplane, and the axial profile of magnetic field along the wall. Ampere’s law is solved with actual magnetic field coils, C-2W geometry, and realistic neutral beam sources. An objective function, consisting of comparison between experimental and simulated magnetic fields, is minimized by varying the fast ion sink term until a steady state solution is achieved. The final steady state solution provides a plasma equilibrium with a significant fast ion population. The steady state equilibrium can be used further to estimate the electric field, total energy, and hence for power balance analysis in the new high-confinement operating regime. |
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TP11.00028: Feedback Control of the C-2W Field Reversed Configuration Jesus Romero, Colin Finucane, Sergei Galkin, Kevin Phung, Thomas Roche, Erik Trask C-2W is a linear device [1] producing a field-reversed configuration (FRC) toroidal core surrounded by a mirror confined open field line scrape-off-layer (SOL) plasma. |
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TP11.00029: Neutral Beam Injection on C-2W James Titus, Sergey Korepanov, Dima Osin, Anthony Cooper, Angel Rios, Ivan Isakov, Jesus A Romero, The TAE Team In TAE Technologies' current experimental device, C-2W (also called "Norman"), record breaking, advanced beam-driven field-reversed configuration (FRC) plasmas are sustained in steady state utilizing variable energy neutral beams, advanced divertors, edge-biasing electrodes, and an active plasma control system.1 The ensemble of neutral beam injectors (NBI) includes: four static energy 15 keV, 140 A H/D beams, four tunable energy 15-40 keV, 150 A H/D beams, and one diagnostic 40 keV, 15 A beam. Traditionally, NBI provides heating, current drive, and fuel to a plasma system. On C-2W, the heating beams provide stability and sustainment, as well. We will present recent experimental observations of NBI effects on plasma stored energy, and we will report updates on utilizing feedback control of NBI in conjunction with other control systems and the use of multiple diagnostics to measure plasma quantities. |
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TP11.00030: Observation of Fast Ion Tail Using Neutral Particle Analyzer in C-2W Shuji Kamio, Erik Granstedt, Ryan Clary, Gabriel Player, Sergey Korepanov In C-2U experiments, thermal ion acceleration by a beam-driven wave was observed [1]. This thermal ion acceleration is pointed out to dramatically enhance the fusion rate because the beam energy is transferred to thermal ions, bypassing the electron channel and related loss mechanisms. |
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TP11.00031: Effect of mirror and confinement vessel fields on the power flows from biased electrodes to the FRC electrons Manjit Kaur, Erik Trask, Deepak Gupta, Peter Yushmanov, the TAE team In TAE Technologies’ experimental device, C-2W [1], record-breaking, advanced beam-driven field-reversed configuration (FRC) plasmas are produced. Long-lived, hot FRCs with large excluded flux radius are sustained in steady-state in the central confinement vessel by utilizing several advanced subsystems. These subsystems include variable energy neutral beams, advanced divertors, open field-line biased electrodes, variable axial magnetic fields with mirrors, a fueling setup, and an active plasma control system. In this presentation, we discuss dynamic biasing experiments used to infer power flows into FRC electrons from the biasing system at different mirror strengths and confinement vessel fields. The ionization of gas near the end electrodes creates high-energy electrons in the midplane due to the large axial potential between the electrodes and the confinement region. The presence of high-energy electrons is supported by the observation of high-energy x-rays in the confinement vessel that can couple energy to bulk electrons likely via beam-plasma/two-stream instability. With an increase in mirror strength, the fraction of the electrons passing through the mirror would drop, resulting in reduction in the power coupling to the FRC electrons. |
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TP11.00032: Upgrade of magnetized coaxial plasma gun system to generate high flux spheromak Tadafumi Matsumoto, Thomas Roche, Ian A Allfrey, Hiroshi Gota, Manjit Kaur, Leslie Webber, Masaaki Yamada, Jongsoo Yoo, Sayak Bose, Hantao Ji Magnetized coaxial plasma guns (MCPGs), also known as compact toroid injectors (CTIs), can control the total trapped flux of the ejected spheromak by adjusting the initial stuffing field between the electrodes. TAE technologies developed MCPGs for TAE's C-2 series devices, as part of the particle fueling system [1]. We also conducted spheromak merging experiments using two MCPGs on the CTI testbed [2] and reported that it is possible to generate an FRC by colliding two spheromaks. Ejected spheromaks have a maximum flux of 1 mWb and lose some flux before CTs collide. The upper limit of the trapped flux generally depends on the geometry of the electrode design [3]. In order to expand the operating regime with high trapped flux, we redesigned the electrodes. New electrodes are 3x larger and the stuffing coil energy has been increased to improve attainable flux. By using this new MCPG configuration, we expect that the upper limit of the trapped flux can expand up to 15 mWb. We will present the details of the upgraded MCPG systems as well as preliminary results of spheromak formation. |
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TP11.00033: Orbit-Space Integrated Data Analysis of Fast Ions in the C-2W Field Reversed Configuration Gabriel Player, Sean Dettrick, Erik Granstedt, Richard M Magee, Bradley S Nicks, Toshiki Tajima The C-2W advanced beam-driven field reversed configuration (FRC) device utilizes 15-40 keV neutral beams to create a large population of fast ions, which are critically important for FRC heating, current drive, and stabilization. [1, 2] The suite of fast ion diagnostics on the C-2W device include neutral particle analyzers (NPAs), scintillating neutron detectors, silicon proton detectors, and particle bolometers. Fast and accurate diagnostic modeling techniques are vital to developing an understanding of these fast ion diagnostic signals, and how they relate to fast ion dynamics. We present an integrated data analysis (IDA) paradigm which utilizes weight functions to model these signals. Fast ion orbits in high-beta FRCs are well described by two conserved variables, which allows for the development of two-dimensional “orbit-space” weight functions which fully represent the diagnostic sensitivity, instead of the full four or six dimensions required by many traditional methods. Combined with Monte Carlo particle simulations, they provide a powerful tool for rapid modeling of fast ion diagnostics in an integrated framework with other diagnostic information. We also utilize this newly-developed IDA model to infer properties of the fast ion distribution and explore fast ion dynamics, utilizing both forward simulations and experimental data. |
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TP11.00034: Simulation of 2D electrostatic presheath potential in FRC SOL Wenhao Wang, Xishuo Wei, Zhihong Lin, Sean Dettrick, Calvin Lau, Toshiki Tajima The electrostatic presheath potential in the scrape-off layer (SOL) of a field-reversed configuration (FRC) could affect the turbulent transport in the SOL and the penetration of divertor biasing to the FRC confinement region. Full-f gyrokinetic simulation is needed to find the SOL equilibrium including presheath potential, which is intrinsically 2D resulting from the balance between radial and parallel transport. We have formulated an electrostatic simulation model for the SOL pre-sheath and implemented in the GTC-X code. The model has first been verified in a 1D presheath simulation on a single flux surface by recovering the parallel force balance and continuity equation. To further construct a 2D presheath, different radial boundary conditions and simulation domain size have been tested. With the absence of radial coupling between flux surfaces such as radial current, the radial electric field profile is mainly determined by the boundary condition at the divertor. To capture the penetration of the divertor biasing, a resistive radial current model is proposed to determine a more realistic 2D structure of the presheath potential. By including the 2D presheath as background time-independent equilibrium, we have carried out microturbulence simulation in the FRC SOL and found that the radial electric field of the presheath can reduce the ITG instability by providing a considerable ExB shearing rate. |
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TP11.00035: Inductive Probe Measurements in an RMF FRC Thruster Christopher L Sercel, Tate M Gill, Benjamin A Jorns The Rotating Magnetic Field (RMF) thruster is an example of an inductive pulsed plasma thruster which employs a rotating magnetic field to generate an azimuthal current in a plasma. This current then interracts with magnetic fields, including an applied bias field and self-induced fields, via the Lorentz force to produce plasmoid compression and thrust. In an ideal setting, a Field-Reversed Configuration (FRC) plasmoid is formed before the plasma slug is accelerated, which has the potential to reduce wall interractions through its confining magnetic field structure. The RMF thruster is thought to share many common characteristics of other inductive pulsed propulsion devices, including high power density, throttleability, and compatibility with exotic propellants. However, recent performance measurements show poor total efficiency (<1%), prompting investigation into the acceleration mechanism. In this work, we experimentally investigate the induced magnetic field structure to quantify the magnitude of the induced azimuthal current throughout the pulse. We find evidence of high (>2500 A) driven current and plasmoid formation. We also investigate the impact of flux conserving surfaces on the magnetic field structure and quantify their effect on the Lorentz force on the plasma slug. |
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TP11.00036: The TriForce Project: Progress and Plans Adam B Sefkow, John G Shaw, Ayden J Kish, Michael J. Lavell, Andrew T Sexton, Robert Masti We report on development progress of our particle-based hybrid fluid-kinetic simulation framework named TriForce. The GPU-accelerated code seeks to recover results from both radiation-magnetohydrodynamic and fully kinetic codes, as well as operate in between where both descriptions may co-exist and interact. Our group uses TriForce to investigate a range of topics in fields such as inertial confinement fusion, magneto-inertial fusion, magnetic confinement fusion, and high-energy-density physics. The goal of the TriForce Center for Multiphysics Modeling is to provide better predictive capability and access to modern and parallelized models for the benefit of the academic community. The current status of the project and its applications will be surveyed. |
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TP11.00037: Projections of spheromak configurations sustained with steady, inductive magnetic helicity injection (SIHI) toward high Lundquist number Derek A Sutherland, Christopher J Hansen, Aaron C Hossack, Kyle D Morgan The spheromak plasma configuration offers a potential pathway toward compact and simple magnetic fusion energy systems without the toroidal field coils (TFCs) or central solenoid (CS) characteristic of tokamaks. Due to the usage of large magnetic field-normalized plasma currents, spheromaks offer the potential for ohmic ignition provided sufficient energy confinement is achieved. For a spheromak system to operate continuously, both an equilibrium field coil (EFC) set and some method for plasma current drive are needed. Steady, Inductive Helicity Injection (SIHI) is actively being developed to efficiently sustain spheromak plasma currents while directly driving non-axisymmetric dynamics needed for MHD dynamo current drive. Based on recent data from both the HIT-SI3 and HIT-SIU experiments and supporting computational works, projections of SIHI-driven spheromak configurations toward high Lundquist number will be presented. These scaling laws are used to support the envisioned design point for a next-generation Proof-Of-Concept (POC) device that aims to demonstrate the highest core triple product and core ion and electron temperatures for the spheromak concept to-date with pulse lengths of ~ 50 - 100 ms. |
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TP11.00038: Electron density and ion temperature measurements of HIT-SI3 and HIT-SIU spheromak plasmas Aaron C Hossack, Kyle D Morgan, Joshua B Perry, Jamie L Xia, Christopher J Hansen, Derek A Sutherland The HIT-SI3 and subsequent HIT-SIU devices study application of steady inductive helicity injection, using multiple injectors driven with frequencies in the 10's of kHz, to form and sustain spheromak plasmas. The final run campaign of the HIT-SI3 experiment at the University of Washington produced discharges with record performance, including toroidal plasma current exceeding 100 kA, the first experimental observations of peaked plasma density profiles during sustainment as measured by a new multi-chord interferometer, and impurity ion temperatures up to 40 eV. Comparisons to initial results from the new HIT-SIU experiment, which provides additional control over the applied mode spectrum and plasma density, will be presented. |
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TP11.00039: Inductively driven helicity injection with non-axisymmetric perturbation control Kyle D Morgan, Aaron C Hossack, Joshua B Perry, Christopher J Hansen, Derek A Sutherland The HIT-SI (2005-2013), HIT-SI3 (2013-2021), and HIT-SIU (2021-present) devices use sets of inductively driven helicity injectors to form and sustain spheromak plasma equilibria. Each injector is a semi-toroid connected to the main confinement volume and is operated by two sets of coils oscillating in phase to inductively inject magnetic energy and helicity. The HIT-SIU device additionally features a toroidal geometry connecting the four injectors to provide additional control over operation. The toroidal spectrum of the imposed perturbation depends primarily on the geometry of the helicity injectors and the relative temporal phase of the helicity injection waveforms, with a variety of spectra involving n=1, n=2, and n=3 perturbations [1]. Experimental results from the three injector configurations are compared with Taylor state equilibria (PSI-Tet) and dynamic extended MHD models (NIMROD) of the plasma. |
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TP11.00040: Inductively-Coupled Preionization Sources for the HIT-SIU Spheromak Experiment Joshua B Perry, Aaron C Hossack, Kyle D Morgan, Christopher J Hansen, Derek A Sutherland, Jamie L Xia The HIT-SI3 and HIT-SIU plasma experiments are designed to study spheromak plasmas created and sustained through steady inductive helicity injection. The oscillating fields inside the inductive helicity injectors tend to expel plasma inside them, meaning that it must constantly be replenished to avoid starvation. HIT-SI3 accomplished this by injecting neutral gas using puff valves and relying on Paschen breakdown for initial ionization, limiting the range of accessible densities. The HIT-SIU experiment attempts to expand the range of accessible operating densities by supplementing its neutral sources with a set of high power inductively-coupled plasma sources to feed pre-ionized gas into the injectors. This system aims to improve control of plasma density, which has a strong impact on current drive performance. The electron density and temperature inside the sources was measured across a range of values for applied magnetic field and input power, demonstrating a high-density, uniform source plasma for the injectors, over a wide range of fueling rates. Results comparing operation of HIT-SIU, with and without pre-ionization sources, will be presented along with comparison to the HIT-SI3 experiment. |
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TP11.00041: MHD simulations of inductive helicity injection in HIT-SIU using realistic low-impedance circuit boundary conditions Christopher J Hansen, Aaron C Hossack, Kyle D Morgan, Derek A Sutherland Due to the complexity of current drive mechanisms in inductive helicity injection, numerical simulations are vital to understanding present results and extrapolating to future devices. Numerical simulations of the HIT-SI(3) experiments using Hall-MHD models in the NIMROD and PSI-Tet [1] codes have produced good agreement with experimental observations. However, differences remain in several important quantities (eg. mean current and magnetic profiles). Prior simulations used a “high-impedance” boundary condition for some circuits in contrast to their experimental properties. This difference is important as significant feedback between plasma dynamics and driven circuit waveforms is observed, with increased coupling present in the newly commissioned HIT-SIU experiment. Improvements to the injector boundary conditions have been developed to enable “low-impedance” boundary conditions for all injector coils to provide a more complete circuit-to-plasma model. Development of this model and results from simulations of HIT-SI3 and HIT-SIU will be presented, focusing on experimental comparison and validation. |
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TP11.00042: One dimensional gyrokinetics of a high-field magnetic mirror Manaure Francisquez, Noah R Mandell, Maxwell Rosen, Ammar Hakim, Gregory W Hammett, Cary B Forest Magnetic mirrors have achieved MHD stability in the last two decades thanks to a combination of expanded flux regions at the ends, clever use of line-tying, biasing, sloshing ions and other strategies [1]. The increased stability and enhanced heating has allowed modern mirrors to approach the keV electron temperature milestone [2]. Leveraging this knowledge, and the latest advancements in high-temperature superconducting (HTS) technology, the Wisconsin HTS Axisymmetric Mirror (WHAM) aims to produce a compact device with fusion relevant energy densities and inform the feasibility of mirror-based fusion plants. These mirrors rely on the formation of a strong positive potential produced by the initial rapid loss of electrons due to their larger scattering frequency [3] to enhance electron confinement. In this work we present two types of one-dimensional (along a field line) simulations with Gkeyll's gyrokinetic solver [4], one with kinetic electrons and the other with adiabatic electrons, through which we examine end-losses and the self-consistent formation of the (Pastukhov) potential. Results are compared to previous analytical approximations based on Fokker-Planck calculations in the central region of the plasma [5]. Lastly, we discuss the challenges associated with the continuum gyrokinetic modeling of high-field mirror plasmas and the three-dimensional study of microturbulence in these devices. |
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TP11.00043: One dimensional gyrokinetics of a high-field magnetic mirror Maxwell H Rosen, Manaure Francisquez, Noah R Mandell, James L Juno, Ammar Hakim, Gregory W Hammett Magnetic mirrors have achieved MHD stability in the last two decades thanks to a combination of expanded flux regions at the ends, clever use of line-tying, biasing, sloshing ions and other strategies [1]. The increased stability and enhanced heating has allowed modern mirrors to approach the keV electron temperature milestone [2]. Leveraging this knowledge, and the latest advancements in high-temperature superconducting (HTS) technology, the Wisconsin HTS Axisymmetric Mirror (WHAM) aims to produce a compact device with fusion relevant energy densities and inform the feasibility of mirror-based fusion plants. This experiment relies on the formation of a strong positive potential produced by the initial rapid loss of electrons due to their larger scattering frequency [3] to enhance electron confinement. In this work, we present two types of one-dimensional (along a field line) simulations with Gkeyll's gyrokinetic solver [4], one with kinetic electrons and the other with adiabatic electrons, through which we examine end-losses and the self-consistent formation of the (Pastukhov) potential. These gyrokinetic simulations are compared against a kinetic simulation which resolves $v_\|$ and uses a fluid equation for the evolution of $T_\perp$. Results are compared to previous analytical approximations based on Fokker-Planck calculations in the central region of the plasma [5]. Lastly, we discuss the challenges associated with the continuum gyrokinetic modeling of high-field mirror plasmas and the three-dimensional study of microturbulence and interchange turbulence in these devices. |
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TP11.00044: Construction Status of the Wisconsin HTS Axisymmetric Mirror Jay K Anderson, Mike R Brown, Mike Clark, Douglass Endrizzi, Cary B Forest, Mykola Ialovega, Jeremiah Kirch, Grant Kristofek, Steve F Oliva, Jonathan D Pizzo, Oliver Schmitz, Kunal Sanwalka, Danah Velez, John P Wallace, Mason Yu A new magnetic mirror (WHAM) is under construction at UW-Madison with the primary mission of achieving MHD- and kinetically- stable plasmas in a low-collisionality regime, where the particle confinement increases rapidly with average ion energy. Axisymmetric MHD stability is achieved via biasing end rings with respect to a central limiter (the vortex confinement scheme) and will allow modest plasmas in initial experiments, and electron temperature approaching 1 keV following the boost of the central magnetic field in the 2nd experimental phase. Scenarios have been developed for fast ion deposition via neutral beam injection whose energy can be increased via rf heating, and electron cyclotron resonant startup in the strong field device. Here we report on construction status of the machine, magnets, and major auxiliary heating systems. |
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TP11.00045: Investigating MHD stabilized mirror configurations with theory and simulations Douglass Endrizzi, Jay K Anderson, Mike R Brown, Ari Le, Jonathan D Pizzo, Kunal Sanwalka, Danah Velez, Mason Yu, Cary B Forest Stabilizing the MHD interchange mode is fundamental to all mirror traps. With growth rates around an inverse ion bounce time ($\gamma \sim v_i/2 L$), this mode is lethal before any meaningful plasma can be made. The WHAM (Wisconsin High-temperature superconductor Axisymmetric Mirror) experiment anticipates $\gamma \sim 500$ kHz for a 10 keV Deuterium plasma in a 1 m device. It plans to use shear flow stabilization, which has been shown in several other experiments to saturate the $m=1$ interchange mode at small amplitude, rendering it harmless. However, some theoretical work predicts that a successful WHAM experiment may access regimes where shear-flow stabilization is insufficient. In anticipation, this work explores through application of theory and VPIC simulations alternative options, including high plasma beta effects, feedback stabilization (inductive and electrostatic), and the use of divertor geometries. Each of these options can lead to non-adiabaticity and rapid loss of the fusing fast ions. I will present research analyzing the trade-offs between these stabilization schemes and fast-ion confinement in realistic device geometries. To verify these results, several experiments will be proposed for the WHAM device. |
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TP11.00046: Status and Modeling of Electron Cyclotron Heating systems for the Wisconsin HTS Axisymmetric Mirror Jonathan D Pizzo, Cary B Forest, Jay K Anderson, Mike Clark, Steve F Oliva, John P Wallace, Roderick E McNeill, Kunal Sanwalka, Mason Yu, John Lohr, James Anderson, Kurt Zeller The Wisconsin HTS Axisymmetric Mirror (WHAM) is a high-field magnetic mirror under construction at UW-Madison. This device will use Electron Cyclotron Heating (ECH) for a variety of functions including breakdown, reducing fast ion slowing down, and achieving an electron temperature greater than 750 eV. An overview of the ECH system in WHAM will be presented including the 1 MW, 110 GHz gyrotron system, the waveguide run, and a rotatable launching structure which will aim ECH at different radial locations in the plasma. The current state of modeling for ECH waves using the Genray ray tracing code and CQL3D Fokker Plank solver will also be discussed, with emphasis on how ECH can create different Te profiles and what effect this can have on MHD stability in a vortex confined mirror plasma. Further discussion will detail how ECH may draw out a high energy tail of electrons, the effects of such on stability, and the diagnostic signatures it may produce. The focus will be on a high field side, fundamental X mode launch for which modeling shows >95% absorption, however alternative launch scenarios with up to 90% absorption under high density conditions are also examined. Lastly, results from gyrotron testing into vacuum waveguide will be shown. |
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TP11.00047: Neutral Beam Injection Experiments: modeling and fusion product diagnostics on Heating on WHAM Kunal Sanwalka, Cary B Forest, Jay K Anderson, Jonathan D Pizzo, Douglass Endrizzi, Mason Yu, Robert W Harvey, Yuri V Petrov The Wisconsin HTS Axisymmetric Mirror (WHAM) will utilize advances in high temperature superconductors and recent physics developments to explore the feasibility of axisymmetric magnetic mirrors as a fusion power-plant. WHAM will use neutral beam injection (NBI) to create a sloshing ion population that will confine a warm plasma in the center which helps with kinetic stability and creates a peaked reactivity profile which will be used for plasma facing materials testing. This sloshing population will be diagnosed with fusion product diagnostics including a neutron detector and proton detector array. Modelling is done via CQL3D (a Fokker-Planck diffusion equation solver) to capture the non-thermal effects of a beam dominated plasma. We present the latest simulation results, focusing on the effect of different density and temperature profiles, NBI parameters and RF heating have on the reactivity profile. We also present the current status of fusion diagnostics, emphasizing their ability to spatially resolve the plasma density, temperature and fusion reactivity as well as future upgrades for WHAM-0.8. |
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TP11.00048: Full Wave Modeling of HHFW Heating for WHAM Mason Yu, Cornwall H Lau, John C Wright, David L Green, Cary B Forest, Jay K Anderson The Wisconsin HTS Axisymmetric Mirror (WHAM) experiment will utilize up to 1 MW of High Harmonic Fast Wave (HHFW) heating power in the Ion Cyclotron Range-of-Frequencies (ICRF) to preferentially create a high energy sloshing ion population. To provide quantitative predictions of antenna loading and the wave field profile while capturing accurate geometric features, a full wave Finite Element Method (FEM) model has been constructed based on COMSOL Multiphysics' RF module. The model utilizes a cold plasma dielectric tensor with artificial damping, and we will report on the progress of implementing and validating an external iterative solver in which a hot plasma dielectric tensor with a bi-Maxwellian ion distribution function is used to account for parallel spatial dispersion and finite Larmor radius effects. Results from 2D axisymmetric and 3D simulations will be compared across scenarios with different source frequency, plasma density and temperature profiles. Based on these results, a preliminary single loop antenna and transmission line design will be shown along with predicted antenna loading. Finally, the effect of scrape-off layer thickness and density on antenna loading will be demonstrated. |
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TP11.00049: Exploring novel electromagnetic algorithms for efficient Hybrid Fluid-Kinetic Multiphysics Simulations Andrew T Sexton In particle-based fluid-kinetic plasma simulations1, an electromagnetic field solver is coupled to the particles via a mesh. Explicit finite-difference time-domain (FDTD) methods solve Maxwell's equations and require very small time steps when high-resolution meshes are used. Long time-scale simulations might require 105-107 time steps in order to reach the hydrodynamic time of interest. A critical area of research is to accelerate these computations using GPU hardware. The use of implicit methods generally requires additional operations to solve banded matrices and has more complex algorithm design, but benefits by being unconditionally stable and unrestricted by the need to resolve the speed of light on the mesh. This enables larger time steps and shorter computation times. The fundamental locally one dimensional complying divergence (FLOD-CD-FDTD2) method is an unconditionally stable semi-implicit noniterative method. We report on our efforts to test this and similar algorithms for accuracy, efficiency, memory use, and how well they can be accelerated and parallelized. Our goal is to stably and accurately achieve very long simulation times for ICF, HEDP, and MFE applications. |
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TP11.00050: A staged pre-ionization approach for Field-Reversed Configuration formation on MSX-II Ian A Bean, John C Boguski, Colin S Adams, Thomas E Weber The density, temperature, flux retention, and stability of an equilibrium Field-Reversed Configuration (FRC) strongly depend on the parameters of the pre-ionized plasma prior to field-reversal. Pre-ionization studies on the new MSX-II experiment at Los Alamos National Laboratory are investigating the impact of the pre-reversal plasma density, purity, and uniformity on the FRC parameters after reversal. The first pre-ionization studies use a staged process, first firing an annular array of coaxial rail guns to inject a weakly ionized gas, followed by an inductively coupled ringing multipole to achieve full ionization. Results are compared to those of the MSX-I experiment, which used the same annular array of coaxial rail guns but followed with a ringing-theta method to achieve full ionization. |
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TP11.00051: Zap Energy Shear Flow Stabilized Z Pinch Reactor Results and Concept Benjamin J Levitt, Brian A Nelson, Uri Shumlak The sheared-flow stabilized (SFS) Z-pinch concept, developed at University of Washington with LLNL collaborators, is now on a path to commercialization at Zap Energy. Recent experiments corroborate expected thermonuclear fusion reaction rates, as the discharge current is scaled towards compact reactor conditions. The Fusion Z-pinch Experiment (FuZE) employs high power-handling electrodes, flexible gas injection, and independently-switched capacitor bank modules to tailor the discharge current and gas distribution to establish stabilizing sheared flow and pinch current. Experimental campaigns are underway to increase the pinch current, stability duration, and DD fusion neutron production. We’ve recently achieved record pinch currents, > 500 kA, electron temperature > 2 keV, ion temperature > 2.5 keV and neutron yield > 2e8/pulse. These efforts aim to scale the pinch current, plasma density, and plasma temperature to reach scientific breakeven by 2023 in the next generation device FuZE-Q, which is now operational. Scientific and engineering status of both experimental platforms will be discussed. |
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TP11.00052: X-ray Diagnostics for the Flow-Shear-Stabilized Z-Pinch Lucas A Morton, Aria R Johansen, Glen A Wurden, Anton D Stepanov, Chelsea Liekhus-Schmaltz, Will McGehee, Benjamin J Levitt Two multi-foil X-ray probes for electron temperature measurements have been fielded on FuZE. The probes consist of 7 thick Si PIN photodiodes, each with separate foils, optimized for measuring temperatures of order 1 keV. The probes also contain paired filters that allow detection of the presence of higher-energy X-rays (10-20 keV). Relative calibration of the detector sensitivities & estimation of the error due to the imperfect overlap of each diodes’ field of view are provided by testing with uniform filters applied to all channels. A Bayesian analysis process is implemented using non-informative priors. |
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TP11.00053: Radiation Emission and Evolution of Sheared-Flow-Stabilized Z-Pinches on FuZE and FuZE-Q Aria Johansen, Pi-En Tsai, Amanda E Youmans, Lucas Morton, Glen A Wurden, Drew P Higginson, Uri Shumlak Sheared-flow-stabilized Z-Pinches FuZE and FuZE-Q produce high energy photons and neutrons. The soft X-rays are detected by XUV photodiodes with foil filters, allowing for the transmission ratios to be taken to give information about the temperature of the plasma. Neutron yields are determined by various activation detectors. A series of 4 similar rhodium activation detectors gives spatial resolution of the devices’ neutron generation, while an arsenic activation detector gives a more sensitive though spatially less resolved measurement of the yield. In addition to numerous fast plastic scintillators, a set of organic glass pulse shape discriminating scintillators measure neutron energies, assuring that there is no signal contamination of the spectroscopic data from prompt gammas created by neutron interactions with surrounding materials, or other high energy photons produced by the machines. This suite of detectors are used for monitoring the evolution of the radiation emitted, and the optimization of the performance of the two fusion reactor concept devices. |
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TP11.00054: Measurements and Monte Carlo Simulations of DD Fusion Neutrons Generated by FuZE Pi-En Tsai, Aria Johannsen, Amanda E Youmans, Drew P Higginson, Brian A Nelson, Benjamin J Levitt The Fusion Z-pinch Experiment (FuZE) employs the sheared-flow-stabilization concept to form plasma pinches at Zap Energy. Neutral deuterium gas injected into the machine is ionized, gains energy from the capacitor banks, and then induces nuclear fusion reactions that emit 2.45-MeV neutrons as one of the reaction products. The neutron spatial and energy distributions can be used to better understand the properties of the constituent fusion fuel. Fast plastic scintillators coupled with photomultiplier tubes are used to measure the DD fusion neutrons at FuZE. In addition, FuZE is modeled in the Monte Carlo radiation transport code - PHITS, and the detector responses are simulated in aid of determining the origin of the neutrons. The comparison of the measurements and the simulation results with various FuZE experimental parameters, which include the gas injection timing, gas injection pressure, bank voltages, etc., will be presented. |
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TP11.00055: Optical tracking of Low-Z Impurities in a Stabilized Z Pinch through EUV-VIS Emission Andrew Taylor, Aidan W Klemmer Measurement of impurity ion parameters (ne, ni, vi, B, etc.) via optical emission is an easily-accessed method of inferring the plasma conditions in a high-density, high-temperature deuterium plasma. Previous optical diagnostics on the FuZE shear-flow-stabilized Z pinch included high-resolution Ion Doppler Spectroscopy of C III/C V lines (227 & 229 nm) in conjunction with a Hadland 12-frame ICCD fast framing camera in the 350-900 nm region. These diagnostics provide high spectral resolution and nanosecond time resolution at the cost of limited understanding of the entire snowplow and quiescent period of pinch formation in FuZE. To rectify this limitation, two additional diagnostics will be fielded on FuZE-Q to track impurity movement across a long timescale and a wide spectral range. A vacuum EUV spectrometer with multichannel gating will be able to collect a sequence of spectra in the pinch formation region from excited-state C V and O VII emission in the 9-19 nm range as well as C VI and O VIII ground-state transitions in the 1.5-5 nm range. This will complement the current spectroscopic measurements of C V in the UV range, which can be compared against theoretical spectra. In addition, a fast framing Shimadzu camera, capable of 128 frames at 100 ns each, will be used to track carbon and oxygen impurity motion. A selection of narrow bandpass filters will provide the ability to select individual impurity emission lines (C II, C III, C V, O III, D-beta, etc.) instead of viewing the entire 200-900 nm emission profile. Initial spectra and images are presented. |
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TP11.00056: Two-fluid modeling of linear and nonlinear stability of the sheared-flow-stabilized Z pinch Eric T Meier, Uri Shumlak Five-moment two-fluid modeling is used to generate new insight into stability of the sheared-flow-stabilized Z pinch. Simulation results [1] identify linear and nonlinear behaviors that may enable long-lived quiescent Z-pinch plasmas. In sheared plasmas that are linearly unstable, nonlinear relaxation leads to stable quasi-equilibrium conditions in both 2D and 3D simulations. Key features of previous PIC results for linear stability are reproduced, opening the possibility of whole device modeling with physical fidelity comparable to kinetic simulations. Modeling is done in the high-order discontinuous Galerkin WARPXM framework [2], beginning from Bennett equilibrium profiles that approximate observed plasmas in the FuZE experiment. Instability growth rates, with varying degrees of radially sheared axial flow, agree closely with prior results for linear growth. In the nonlinear phase of the instabilities, sub-Alfvenic sheared flow drives mixing that yields quasi-equilibrium conditions. Such quasi-equilibria provide a cornerstone for more completely understanding and exploiting sheared-flow stabilization of the Z pinch as it is scaled toward fusion reactor conditions. |
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TP11.00057: Whole-Device Modeling of the FuZE Device I. A. M. Datta, Eric Meier, Uri Shumlak, Peter Stoltz, Noah Reddell, Nolan van Rossum, Anton D Stepanov, Lucas Morton, Morgan Quinley, Aria R Johansen, Pi-En Tsai Simulations of the sheared-flow-stabilized (SFS) Z-pinch device (FuZE) aid experimental efforts by contributing to interpretation of diagnostic data as well as providing predictive capability needed for continuing design work. Current work focuses on leveraging magnetohydrodynamics (MHD) to perform whole-device modeling using the WARPXM finite-element code for cases of FuZE shots up to 500 kA with an initial slug of plasma as well as injection of a plasma source. This provides a relatively computationally inexpensive way to understand the plasma dynamics in the device. Connection with experiment is made through the development of synthetic diagnostics which can be compared to corresponding efforts on the actual device. These include the calculation of line-integrated densities for comparison with interferometry, magnetic field measurements along the outer electrode for comparison with Bdot probe data, Bremsstrahlung radiation for comparison with X-ray detectors, and neutron yield calculations for comparison with scintillator data. A circuit model will also be implemented to match the current profiles seen in the experiment. Simulation results including diagnostic comparisons will be presented. |
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TP11.00058: Sheath Effects for Electrode Research at Zap Energy Peter H Stoltz, Eric Meier, Iman Datta, Uri Shumlak, Morgan Quinley The goal of this work is to investigate the electrode sheaths in a high power Z-pinch plasma configuration. A Z pinch is one of the oldest plasma fusion configurations, but Z pinches have always suffered from a series of instabilities that limit their performance. Recently, sheared flow stabilization has resulted in significant stability gains, with some pinches lasting more than 10 us (several thousand linear instability growth times). Zap Energy is currently operating two sheared-flow-stabilized Z-pinch experiments: the Fusion Z-pinch Experiment (FuZE) and a newer, higher voltage, higher current machine, FuZE-Q. As these devices reach higher voltages and currents, the resulting plasma effects on the electrodes may play a key role in the device performance. For example, presently research conditions on FuZE are tens of kV of applied voltage that draws several hundred kA of current through a plasma with density of several times 1023 m-3 and temperature of several keV in a pinch of radius less than a cm. This set of parameters leads to demanding conditions on the anode and cathode. Particle-in-cell simulation offers a way to estimate the sheath size and particle flux at the anode and cathode, the plasma potential, and sputtering rate. We can examine those quantities as we vary the current emitted from the cathode, the magnetic field strength, and the amount of sputtered material. |
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TP11.00059: Phase space eigenfunctions for continuum kinetic simulations Daniel W Crews In weak turbulence the linear eigenfunctions contain most of the fluctuation energy, and this is also true for phase space turbulence in collisionless plasma. In this work, phase space eigenfunctions are studied in the unmagnetized and strongly magnetized regimes. Further, the nonlinear structures, or phase space vortices, corresponding to the linear eigenfunctions are studied. The phase space cascade responsible for anomalous dissipation is composed of such phase space vortices. Here nonlinear structures are presented for Weibel modes of the bi-Maxwellian and electron cyclotron instabilities in loss-cone distributions. In addition, ensembles of randomly phased eigenfunctions are utilized as initial conditions for Vlasov and quasilinear simulations. Such simulations are presented for Langmuir and Weibel turbulence in two-dimensional configuration space. The insights gained from this particular work are discussed in the context of cross-field anomalous resistivity in hot Z-pinch plasmas. |
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TP11.00060: Fusion Power Systems Engineering Program at Zap Energy Matthew C Thompson, Alex Cheung, Vidya Nalajala, Clemente J Parga, Sean C Simpson Zap Energy is rapidly developing the technology of Z-pinch plasma discharges stabilized via sheared flow [1]. The Z-pinch configuration offers the promise of a compact fusion device owing to its simple geometry, unity beta, and absence of external magnetic field coils. In addition to a robust experimental program pushing plasma performance towards breakeven conditions, Zap Energy has parallel programs developing power handling systems suitable for future power plants. Technologies under development in the test stand program include high-average-power repetitive pulsed power, high-duty-cycle cathodes, and liquid metal wall / blanket systems. Our plant design group is simultaneously developing overall power plant architectures, including neutron flux modeling. |
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TP11.00061: Improved S/XB Measurements on the Sheared-Flow-Stabilized Z-Pinches at Zap Energy Clyde J Beers, Andrew Taylor, Sean C Simpson, Ben Levitt, Matthew C Thompson Electrode erosion rates on the Fusion Z Pinch Experiment (FuZE) device at Zap Energy, which makes use of sheared-flow stabilization, are important to know for determination of the component lifetime. An in situ erosion measurement using the ionizations per photon (S/XB) technique is presented with an updated telescope design. In this work, an ultraviolet spectrometer coupled to an in-house built telescope via a multi-cord fiber optic cable is used to measure the sputtering across the electrode faces. The small size of the pinch (~1 mm radius) makes it important to understand where the telescope is pointed with respect to the electrode attachment location and the telescope design allows for sub mm scanning across the surface. The design, calibration, and experimental setup is discussed and comparison to the calculated physical sputtering yields is also presented. |
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TP11.00062: Spectroscopic investigation of plasma-material interactions on the ZaP-HD sheared-flow-stabilized Z-pinch device Amierul Aqil b Khairi, Bennett H Diamond, Eric T Meier, Uri Shumlak High energy density plasma-material interactions occur on the ZaP-HD sheared-flow-stabilized Z-pinch device. In particular, erosion of the graphite cathode contributes to impurity production and limits the lifetime of the component. Understanding the plasma-electrode interaction is critical for ongoing work in scaling the concept to a reactor device and the associated increase in energy density. Spectroscopic methods provide in-situ, non-perturbing measurements of various parameters in this extreme environment. A fast-framing camera coupled to a Czerny-Turner spectrometer provides time-resolved relative intensity measurements of impurity ions over a range of spatial locations. These can also be used to calculate plasma temperature and velocity near the cathode. In addition, a CCD camera and PMT provide a time-integrated spectrum and time-resolved intensity respectively for a single impurity line. Together, these instruments characterize the spatiotemporal distribution of impurity ionization stages. These results will support implementation of the ionizations per photon (S/XB) method to infer sputtered impurity flux. |
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TP11.00063: Multichannel Radial Transport Simulation of a Rapidly-Rotating Axisymmetric Plasma Myles Kelly, Ian G Abel The Maryland Transport Solver (MTS) is a one-dimensional numerical framework with the goal of providing a predictive scoping and design tool for the Centrifugal Mirror Fusion Experiment (CMFX). MTS solves the simplified transport equations of a centrifugally confined, rapidly-rotating plasma in a magnetic mirror from first principles. This framework is an iteration of MCTrans++ [Schwartz, N., et al, 2022, this conference], a zero-dimensional model designed for the same problem. MTS utilizes a one-dimensional, radial, finite-element, Hybridized Discontinuous Galerkin (HDG) model [Nguyen, N.C., Peraire, J. and Cockburn, B., 2009. Journal of Computational Physics, 228(9), pp.3232-3254 and 228(23), pp.8841-8855.] combined with MCTrans++ to solve for multichannel particle, momentum, and heat transport. The coupling of the transport of such thermodynamic quantities allows the co-dependent nature of their fluxes to be investigated. The SUNDIALS IDA package provides a multi-step implicit backward differentiation formula (BDF) to model the time integration of the equations. Additionally, the plug-and-play nature of the input flux equations allows for the generalization of the numerical framework to any axisymmetric plasma. Thus showing potential for optimization and adjoint method studies for multiple fusion reactor designs. |
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TP11.00064: On the asymptotic equilibrium of a rapidly-rotating Mirror Plasma Ian G Abel Due to the success of the Maryland Centrifugal Experiment (MCX) [R. F. Ellis et. al. PoP 8, 2057 |
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TP11.00065: Overview of the Centrifugal Mirror Fusion Experiment (CMFX) Carlos A Romero-Talamás, Brian L Beaudoin, Adil B Hassam, Timothy W Koeth, Nathan Eschbach, Zachary D Short, Nick R Schwartz, Myles Kelly, Ian G Abel, Debjyoti Basu, Ryan Schneider The goal of CMFX is to azimuthally rotate plasmas in a mirror configuration at supersonic speeds and densities of at least n = 1018 - 1019 m-3 and Te = Ti = 0.5 keV, for 15 ms or longer. An applied voltage across the magnetic field yields an azimuthal E x B drift that has been shown to create stabilizing velocity shear in prior centrifugal mirror experiments. A pair of superconducting magnets are now in place and tested at 3 T fields at the mirror throat and 0.375 T at midplane. The cylindrical chamber with a length of 6.7 m and diameter of almost 0.8 m contains a high-voltage center electrode, tungsten-coated circular grounding limiters, and bucket-shaped insulators to allow for applied voltages of up to 100 kV with an existing capacitor bank. A gas-puff and pre-ionization system will allow for fine control of density. Ion Doppler spectroscopy and interferometric density diagnostics are being calibrated and tested with low temperature plasmas in preparation for high-voltage experiments. Results from first discharge tests as well as future experimental plans to test analytical models and simulations, will be discussed. |
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TP11.00066: High Voltage Power Driver for the Centrifugal Mirror Fusion Experiment Brian L Beaudoin In this work, we present a high voltage power driver scheme that will be used in tandem with the magnetic mirror field to rotate a plasma in the Centrifugal Mirror Fusion Experiment (CMFX) at the University of Maryland. The high voltage power driver would energize a long center electrode placed in the middle of the machine that would create a radial electric field that when crossed with the static magnetic field provided by two superconducting MRI solenoidal magnets, would create a centrifugal force that spins the plasma at high Mach numbers, thus providing axial confinement. This high voltage power driver would nominally operate in a two-stage mode. Initially it would drive the low impedance plasma with a low voltage 10kV capacitor bank and then phase in a separate power supply/capacitor bank that would drive the higher impedance plasma after the initial start-up. Simulations of the future experimental circuitry and results of a previous experiment, the Maryland Centrifugal Experiment (MCX) [R. F. Ellis et. al. Phys. Plasma 8, 2057 (200) & Phys. Plasmas 12, 055704 (2005)] will be presented. |
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TP11.00067: Ion Rotational Velocity Diagnostic for the Centrifugal Mirror Fusion eXperiment Zachary D Short, Nathan Eschbach, Brian L Beaudoin, Carlos A Romero-Talamás A multi-chord ion Doppler spectroscopy (IDS) diagnostic has been developed for the Centrifugal Mirror Fusion eXperiment (CMFX) at the University of Maryland, College Park. The cylindrical, mostly hydrogen CMFX plasma is set into azimuthal E x B rotation in a magnetic mirror. The resulting rotational velocity shear can suppress magnetohydrodynamic instabilities. Therefore, the measurement of ion rotational velocity profiles is critical to the characterization of the CMFX plasma. A fiber-optic array consisting of ten tangential viewing chords is set up to take ten simultaneous line-integrated spectroscopic measurements of the intensity, Doppler broadening, and Doppler shift of introduced impurity helium emission (He II, 468.6 nm) at the midplane. The system is easily reconfigured to measure emission from hydrogen neutrals (H I, 656.3 nm). The diagnostic can be moved to different positions along the axis of symmetry. Radial profiles of emissivity and rotational velocity are obtained via an Abel-like matrix inversion of the spectra. We present the updated design of the IDS system and the inversion method, along with the calibration procedure and initial spectroscopic measurements. |
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TP11.00068: MCTrans++: A Scoping Tool for Centrifugal Mirrors Nick R Schwartz, Ian G Abel, Adil B Hassam, Myles Kelly The centrifugal mirror confinement scheme incorporates supersonic rotation of a plasma into a magnetic mirror device. This concept has been experimentally shown to drastically decrease parallel losses and dampen instabilities as compared to classical mirrors. MCTrans++ is a 0D scoping tool which rapidly models experimental operating points in the Centrifugal Mirror Fusion Experiment (CMFX) at the University of Maryland. |
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TP11.00069: Electron Density Measurements with a Multi-Beam Interferometer at the Centrifugal Mirror Fusion Experiment Nathan Eschbach, Nick R Schwartz, Zachary D Short, Brian L Beaudoin, Carlos A Romero-Talamás First plasma measurements, methods, and future plans for interferometric electron density diagnostics at the Centrifugal Mirror Fusion Experiment (CMFX) are presented. Expected line-integrated densities of 5 x 10^17 to 5 x 10^20 m^-2 will be measured. A single, and eventually multi-beam 1310 nm NIR interferometer will be used at CMFX. Mechanical and optical components will be exposed to fields in excess of 1T. Utilizing a rigid 2D mechanical alignment system, and CMFX’s many near-midplane ports, line integrated density measurements will be possible at multiple axial and radial locations inside the mirror. With verified axial symmetry and reproducible plasmas, Abel inversions can be used to deduce radial density profiles. Density measurements at midplane and near the mirror throat will help track cone losses and validate new theoretical models for transport and stability. Methods and considerations regarding testing, installation, data interpretation, and vibration mitigation will also be discussed. |
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TP11.00070: Digitization of Analog Gauge Readings from Video Footage Autumn T Jackson Bartholomew, Carlos A Romero-Talamás, Landry Horimbere Continuously checking analog gauges manually in high-voltage or high magnetic field environments is neither safe nor efficient. A computer algorithm has been developed to retrieve the position of the dial-pointer of analog gauges from laboratory camera footage. For circular dials, the image is mapped to a linear image and then the pixel position of the pointer is converted to a scale value using a calibration factor. The digitized reading can be logged, plotted, and accessed remotely, and alerts can be sent over the network depending on predetermined thresholds. The program is being implemented in the Centrifugal Mirror Fusion Experiment (CMFX) to digitize and log pressure readings of gauges on superconducting coils and compressors near high-voltage capacitors. |
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TP11.00071: ICF: FAST IGNITION Session Chairs: |
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TP11.00072: Simulating isochoric compression schemes for Proton Fast Ignition using the radiation-hydrodynamics code MULTI-IFE Matthias Brönner, Leonard C Jarrott, Pravesh K Patel, Markus Roth, Florian Wasser, Nils Schott In Proton Fast Ignition (PFI) an inertial fusion target is compressed to densities of the order of hundreds of g/cc using nanosecond-scale lasers. To reach the necessary temperature for ignition, a high-energy proton beam of multiple MeV is focused onto the compressed fusion fuel. In other inertial fusion schemes, the fuel is required to be in an isobaric state at ignition time, which typically involves the creation of a hot spot in the center of the fuel. In PFI the creation of a hot spot by the laser compression is not necessary, due to the ignitor pulse, allowing for an isochoric compression scheme with relaxed conditions. |
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TP11.00073: The T-STAR Experimental Facility for IFE and HED Science at the University of Texas Andrea Hannasch, Sandra Bruce, Ahmed Helal, James Heisler, Doug Hammond, Martin Sokol, Michael M Spinks, Eli Medina, Cris W Barnes, Juan C Fernandez, Leonard C Jarrott, Pravesh K Patel, Markus Roth, Todd Ditmire With the recent demonstration of 1.3 MJ yield at the National Ignition Facility (NIF), the promise of near-term commercialized Inertial Fusion Energy (IFE) has sparked increased interest in new, moderate rep-rate, kJ-class laser facilities for high energy density and plasma physics studies. This enthusiasm has emphasized a gap in the present capabilities of IFE-focused laser facilities. Currently no user facilities deliver multiple kJ beams at repetition rates exceeding a shot per hour, limiting the possible avenues of experimental exploration as well as the level of statistical certainty that these experiments can generate. |
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TP11.00074: ICF: DIAGNOSTICS Session Chairs: |
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TP11.00075: Experimental measurement of planarity of a 1 TPa shock on exit from a shock amplification system rosie l barker, Joshua Read, Matthew Betney, Christian Bradley, Hugo W Doyle, Nicholas Hawker First Light Fusion uses one sided projectile impact to produce fusion within a target cavity. Projectile impact velocities and pressures are of order 10 km/s and 100 GPa respectively. An intermediate shock amplification stage amplifies the pressure incident on the fuel cavity by ~10 times. |
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TP11.00076: Pressure measurement of the amplified shock delivered to an FLF fusion target using VISAR Joshua Read, Sofia Balugani, Jonathan Skidmore, Hugo W Doyle, Nicholas Hawker We report on an experiment designed to measure the output pressure of a First Light Fusion (FLF) amplifier target using VISAR. The amplifier increases the pressure of a projectile-driven planar input shock before it is delivered to the fusion target. Previous experiments at FLF have deduced the amplifier unload pressure within a transparent PMMA block by measuring the output shock position as a function of time using streaked optical shadowgraphy. These measurements are hampered by non-uniformities along the line-of-sight and the inherent noise introduced when differentiating the position-time data. This experiment used FLF's 38 mm two stage light gas gun and an amplifier target to produce a 300-400 GPa shock in water. These conditions are sufficient to transform the water into a metallic-like optical reflector, which has 40-50% reflectivity above 250 GPa. A velocity measurement was made using the shock front in water as a reflector for VISAR. This method is directly sensitive to the shock velocity and allows the pressure profile across the shock to be resolved. We present experimental results and comparisons to simulations performed using our in-house codes. Future improvements to the diagnostic are also discussed. |
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TP11.00077: Accelerating HEDP diagnostic analysis using machine learning without surrogates Avram Milder, Archis S Joglekar, Wojciech Rozmus, Jason F Myatt, Dustin Froula High Energy Density Physics requires robust and repeatable data analysis techniques which provide parameters and uncertainties for workhorse diagnostics such as Thomson Scattering. While gradient descent is an effective technique for solving such optimization problems, when paired with a physical model, it can be computationally cumbersome, especially when the gradients are acquired using finite differences. However, modern scientific computing libraries provide an alternative in the form of Automatic Differentiation(AD). AD enables the performant use of a physical model in conjunction with gradient descent by providing fast, exact gradients and circumvents the need for building and relying on a black-box surrogate model. In this work, Thomson scattering analysis was implemented in an AD-capable framework and showed a significant improvement in runtime by reducing the time to calculate a spectrum and the number of spectrum calculations. This technique can be applied to many inverse problems where an algorithm can effectively describe the physics of a diagnostic. |
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TP11.00078: Mathematical methods for shape analysis of double-shell inertial confinement fusion capsules Saba Goodarzi, Joseph M Levesque, Elizabeth C Merritt, Joshua P Sauppe, David S Montgomery, Eric N Loomis, Noah Dunkley, Paul A Keiter Implosion symmetry is a key requirement in achieving a robust burning plasma in inertial confinement fusion (ICF) experiments. In double shell capsule implosions we are interested in the shape of the inner shell as it pushes on the fuel. Shape analysis is a popular technique for studying said symmetry during implosion. Paired filtering and contour finding algorithms are studied for their promise in reliably recovering Legendre shape coefficients from synthetic radiographs of double-shell capsules with x-ray framing camera noise. What we call the maximum intensity marching squares and the non-local means max(slope) methods are able to recover p0, p2 and p4 maxslope Legendre shape coefficients with mean pixel discrepancy errors of 2.16 and 2.18, respectively, over all noisy synthetic radiographs studied. This improves upon prior radial lineout methods paired with Gaussian filtering which we show to be unreliable and whose performance is highly dependent on input parameters that are difficult to estimate. |
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TP11.00079: Proton Trajectory Assay - Recoil Telescope (PAJARITO) background study on Sandia Z-pinch Facility Tana Morrow, Samual Langendorf, Yongho Kim, Kevin C Yates, Justin Jorgenson, Ramon J Leeper, Matthias Hochanadel, Kevin D Meany, Johnny J Goett, Christopher Prokop The Los Alamos National Laboratory team has led design and validation efforts for a proton recoil telescope for application to experiments at the Z machine at Sandia, for measurement of nuclear reaction history and ultimately resolution of the neutron energy spectrum. This effort has focused on the feasibility of the diagnostic measurement at the yield levels produced by current Z platforms, which amounts to the question of the signal-to-noise ratio that can be obtained. In experiments at Z, there is expected to be significant background signal in terms of the x-ray and gamma ray radiation which is known to be emitted by strongly imploded targets, so the signal-to-noise ratio is described here as a signal-to-background ratio, and ways are sought to maximize the system and detector sensitivity to the recoil protons (signal) and decrease sensitivity to the x-ray and gamma photon emission (background). The Proton Trajectory Assay - Recoil Telescope (PAJARITO) is a diagnostic method to characterize particle beams, making use of the scattering interaction of the beam with an inserted target foil. An approach is being pursued to empirically obtain measurements of the background signal level on candidate detectors in a representative PAJARITO geometry, which can then be used to benchmark radiation MC models and inform the instrument design. This PAJARITO Test Bed has been designed and was fielded on the Z center section in the summer of 2022. The design, integration, and preliminary in-situ measurements of the gamma/x-ray background will be presented. |
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TP11.00080: A Continuous Energy Instantaneous Point Source Model for Implosion Ablator Areal Density Measurements on National Ignition Facility Robert H Dwyer, Kevin D Meaney, Yongho Kim Recent work on Inertial Confinement Fusion (ICF) implosions have focused on measuring the gamma ray emission history from nuclear reactions inside of DT fuel capsules capsule utilizing the gamma reaction history (GRH) diagnostic. The ablator areal density from carbon based ablators <ρR>c has been measured by thresholding the GRH gas cells to resolve the emission from the 16 MeV DT gamma rays and 4.4 MeV gamma rays from metastable carbon through the 12C(n,n’)12mC reaction. These measurements relied on the assumptions of Monoenergetic Instantaneous Point-Source (MIPS) model. The error introduced by this model was found to be acceptable for simple capsule geometries and low fuel <ρR> values found in experiments on the OMEGA-60 laser (100 mg/cm2). For the National Ignition Facility (NIF) ICF experiments however, the larger fuel <ρR> value (500-600 mg/cm2) leads to more down scattered neutrons incident on the ablator. Furthermore, the presence of a holhraum creates a more complex scattering geometry where the DT neutrons interact with the holhraum walls producing more gamma rays incident on the detector. The assumption of the monoenergetic 14.1 MeV energy spectrum in the MIPS model was identified to be one of the largest sources of error in the interpretation of the data. Therefore, a Continuous-energy, Instantaneous, Point-Source model (CIPS) was developed using the MCNP6 code by simulating the down-scattered neutrons for various fuel and carbon <ρR> values for the NIF geometries. This model will allow for more accurate <ρR>c values that have been previously obtained and allow for the identification of trends in capsule performance with <ρR> for NIF shots. |
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TP11.00081: Physics-informed multiprobe instrument for IFE experiments (PiMIX) Zhehui Wang, Karl M Krushelnick, Mark A Foster, Jinsong Huang, Renyuan Zhu, Liyuan Zhang, Eric R Fossum, Jifeng Liu, Francis Alexander, Abul K Azad, Steven H Batha, Gabriella Carini, Matthew Freeman, Haixin Huang, Paul A Keiter, John L Kline, Wenting Li, Eric N Loomis, David S Montgomery, Nga T Nguyen-Fotiadis, Sasikumar Palaniyappan, Robert E Reinovsky, Joshua P Sauppe, Jack S Shlachter, Sky K Sjue, Xin Yue, Sven Vogel, Bradley Wolfe, Dmitry A Yarotski The record-setting MJ neutron yield in the recent NIF experiment opened up a new chapter in burning plasma science and technology. Here we discuss new possibilities that leverage this unprecedented regime of high-energy density laboratory plasmas to advance physics-informed multiprobe instrument (PiMIX), data handling and data interpretation capabilities for IFE experiments. In addition to reconstruction of 3D ICF target implosion movies, our goal is to achieve high-resolution density measurement in the range of one to ten microns, ideally with sub-ns temporal resolution to produce the movies of implosion dynamics. PiMIX will combine multiple-energy photon (X-rays and gamma rays, for example) imaging with neutron and proton measurements to achieve higher information yield than individual diagnostics alone. Initial proof-of-principle measurements will leverage existing LANL and collaborating facilities, new detector capabilities through fast scintillators, perovskites, high-speed imaging sensors, and metamaterial structures. Existing and new data will become available for machine-learning algorithm development and validation. Machine learning and especially physics-informed data-driven algorithms will aim at a unified data pipeline for heterogeneous data processing, constrained by physics models, statistics and the compressed sensing framework. |
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TP11.00082: The MIT HEDP Accelerator Facility for Diagnostic Development for OMEGA, Z, and the NIF Fredrick H Seguin, Patrick J Adrian, Cody W Chang, Skylar G Dannhoff, Tucker E Evans, Timothy M Johnson, Justin H Kunimune, Jacob A Pearcy, Benjamin L Reichelt, Graeme D Sutcliffe, Ernie Doeg, Robert Frankel, Maria Gatu Johnson, Chikang Li, Richard D Petrasso, Johan A Frenje The student-run MIT HEDP Accelerator Facility consists of a 125-keV ion accelerator, DT and DD neutron sources, and two x-ray sources for development and characterization of diagnostics for OMEGA, Z, and the NIF. The accelerator generates DD and D3He fusion products through the acceleration of D+ ions onto a 3He-doped Erbium-Deuteride target, with fusion product rates up to 106 s−1 . The DT and DD neutron sources generate up to 6´108 and 1´107 neutrons/s, respectively. One x-ray generator is a thick-target W source with a peak energy of 225 keV; the other are based on Cu, Mo, or Ti tubes to generate x-rays with a maximum energy of 40 keV. Diagnostics developed and calibrated at this facility include CR-39-based mono-energetic particle radiography, charged-particle spectrometers, neutron detectors, and the particle Time-Of-Flight (pTOF) CVD-diamond-based bang time detector. This poster includes discussion about recent x-ray filter calibration experiments for use in new temporally and spatially resolving x-ray diagnostics PXTD and XRIS for OMEGA, as well as development of precision Step-Range-Filter particle spectrometers for NIF and OMEGA, and analysis techniques for a new Z neutron spectrometer. |
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TP11.00083: Study of krypton helium-β line shifts versus electron density in NIF compressed capsules Kenneth W Hill, M. Bitter, L. Gao, Brooklyn Frances Kraus, P C Efthimion, N A Pablant, M B Schneider, H Chen, D B Thorn, R L Kauffman, D A Liedahl, M J MacDonald, A G MacPhee, S Stoupin, R Doron, E Stambulchik, Y Maron The possibility of using x-ray line shifts instead of Stark broadening to infer electron density (ne) in high ne plasmas has previously been studied theoretically and experimentally for lower Z elements, Ne, Al, and Cl. In this work the time evolution of shifts of the Kr 1s3p1P1 -> 1s2 1S0 He-β spectrum has been measured in NIF compressed capsules using the dHIRES x-ray spectrometer. Densities of 1.8-4x1024 cm-3 were inferred from Stark broadening. Measured line shifts of 5-14 eV were about 60% of theoretical predictions of Li and Rosmej [EPL, 99, 33001 (2012)]. A theoretical understanding of line shifts and broadening and continuum lowering is important for, e.g., dense plasma equation of state and radiative opacity in stellar interiors, inertial confinement fusion, and planetary interiors. |
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TP11.00084: Bayesian Analysis Applied to Neutron Activation Diagnostics Measurements of MagLIF Experiment Michael Mangan, Patrick F Knapp, William E Lewis, Gary W Cooper, Gary M Whitlow, David J Ampleford Neutron activation diagnostics are commonly used to infer neutron yields in inertial confinement fusion experiments (ICF). At Sandia’s Z-Facility, ICF experiments using the Magnetized Linear inertial Fusion (MagLIF) concept are being conducted and activation diagnostics are employed to infer neutron yields. To infer neutron yields from the activation measurements, radiation transport modeling is relied upon to correct for scattering and attenuation present in the experiment that modifies the activation. To understand the likely error involved in those corrections Bayesian methods are used on inferred neutron yield data from a recent MagLIF experiment. |
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TP11.00085: Improving Dante flux measurements with parameterized gold M-band spectral information from NIF experiments* Nicholas D Ouart, James L Weaver, Alexander L Velikovich, Arati Dasgupta, John L Giuliani, Marilyn B Schneider, Klaus Widmann, Michael S Rubery, Mark J May, Gregory E Kemp Dante is a diagnostic used to measure the x-ray drive inside a hohlraum at the NIF. In indirect-drive ICF experiments, a low-Z shell of a small capsule filled with DT is heated and ablated by the x-ray drive, pushing the capsule inward through a "rocket effect." The x-ray drive is generated with laser beams depositing their energy in the non-LTE high-Z plasma created near the hohlraum's interior Au wall. Most of this energy is transferred via conduction to the wall, which becomes heated to a few hundred eV, producing the blackbody radiation to drive the capsule. The non-LTE plasma also emits Au M-band photons, which penetrate deeper into the capsule and can preheat the fuel, thereby significantly reducing the fusion yield. It is essential to measure the time history and spectral shape of the x-ray flux to understand the preheat and mitigate it by doping the capsule shell with a mid-Z element to absorb the Au M-band photons. The unfold can be improved with Au M-band information recorded from the high-resolution Virgil spectrometer. We approximate the recorded spectrum with two Gaussians to use it in the unfold. The x-ray flux and voltages will be presented and compared with the standard Dante unfold. *Supported by DOE/NNSA. This work performed under the auspices of the U.S. DOE by LLNL under Contract No. DE-AC52-07NA27344. DISTRIBUTION A: Approved for public release. Distribution is unlimited. |
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TP11.00086: Laser Optical Imaging Diagnostics for Investigation of Low-Density Plasmas for MagLIF Experiments Joe M Chen, George V Dowhan, Akash P Shah, Brendan J Sporer, David A Yager-Elorriaga, Ryan D McBride One of the major concerns in magnetized liner inertial fusion (MagLIF) experiments on Z is the development of the magneto Rayleigh-Taylor (MRT) instability, which causes degradation to the confinement of thermonuclear fuel. MRT is observed to create helical plasma striations when an axial magnetic field is pre-embedded along the liner with external coils. A hypothesis for the origin of this so-called helical instability is from magnetic flux compression of a low-density plasma (LDP) around the liner originating from the high current densities on the transmission lines leading up to the liner. To study this hypothesis, we are developing a suite of laser-based diagnostics that will provide temporally resolved images as well as density measurements capable of studying LDPs and their interaction onto an imploding liner. The two laser diagnostics under development are a laser schlieren refractometer [2] and a laser interferometer system, both with a 532-nm probe beam from a Nd:YAG laser. We present the development of the optical diagnostic suite along with a surrogate liner experiment used to study LDPs on the University of Michigan's MAIZE facility, a 1-MA class linear transformer driver. |
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TP11.00087: A Case Study of Using X-Ray Thomson Scattering to Diagnose the Plasma Conditions of Laser-Direct-Drive, DT Cryogenic Implosions at Stagnation Hannah Poole, Duc Cao, Reuben Epstein, Igor E Golovkin, Timothy Walton, Suxing Hu, Muhammad Kasim, Sam M Vinko, Ryan Rygg, Valeri N Goncharov, Gianluca Gregori, Sean P Regan The design of inertial confinement fusion ignition targets requires radiation-hydrodynamics simulations with accurate models of the fundamental material properties (i.e., equation of state, opacity, and conductivity). Validation of these models is needed via experimentation. This work presents spatially integrated, spectrally resolved x-ray Thomson scattering as a diagnostic possibility. Previous work focused on currently feasible x-ray sources available on OMEGA to demonstrate this platform's capability of resolving the plasma conditions of the compressed shell at two-thirds convergence. Expanding this work to diagnose peak compression, a different source of x rays is required to overcome the significant self-emission from the imploded target. Here we propose the use of an x-ray free-electron laser (XFEL) source to resolve the plasma conditions induced in the hot spot. Synthetic scattering spectra were generated using 2-D implosion simulations from the LILAC code that were post-processed with the x-ray scattering model that is incorporated within SPECT3D. While an XFEL is not yet available at an ignition-scale laser facility, this work suggests that such a facility would unlock powerful diagnostics capabilities. |
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TP11.00088: Optical spectroscopy of plasma impurities in a megajoule-class Dense Plasma Focus James Young, Clement S Goyon, Aduragbemi A Jibodu, Anthony J Link, Sheng Jiang, Paul C Campbell, Sophia V Rocco, Steven F Chapman, Owen B Drury, Christopher M Cooper, Pierre-Alexandre Gourdain, Andrea E Schmidt A Dense Plasma Focus (DPF1) such as the MegaJOuLe Neutron Imaging Radiography2 (MJOLNIR) is a coaxial deuterium plasma railgun that ends in a z-pinch to produce energetic neutrons. Careful consideration must be given to tracking and maintaining plasma temperatures that maximize neutron yield. Plasma contamination is one mechanism for reducing temperature and thereby reducing fusion events. It has been shown that copper from the anode is sputtered into the plasma during a DPF shot3. However, certain dopants may also increase neutron yield given the proper conditions4. The spatiotemporal location of impurities can be monitored with a spectrometer and compared with numerical results to explore the effect on neutron yield. We present a multi-point, time-gated optical spectrometer capable of differentiating these various mechanisms. Simulations are used to determine laboratory placement of a linear, 27-fiber bundle plug outside the MJOLNIR target chamber. On the detector end a micro-channel plate (MCP) provides light amplification and can be gated for a minimum of 10 nanosecond, which resolves the microsecond DPF dynamics. |
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TP11.00089: ICF: COMPUTATIONAL Session Chairs: |
Author not Attending |
TP11.00090: Vlasov-Fokker-Planck validation studies with ICF-relevant plasmas Steven Anderson, Luis Chacon, Andrei N Simakov The state-of-the-art for simulating high-energy-density (HED) plasma systems, including inertial confinement fusion (ICF) experiments, has been radiation hydrodynamics. Recently, it has become apparent that kinetic (long-mean-free-path) effects – both due to ions and electrons – may significantly impact the evolution of plasmas in HED and ICF contexts. Kinetic simulations of such systems are challenging due to their highly multiscale nature (in space and time), as well as their high dimensionality. The fully kinetic Vlasov-Fokker-Planck code iFP overcomes these challenges with a range of sophisticated numerical strategies [1,2] that make studying such systems tractable. In this work, we present a brief overview of the iFP code, and present several recent validation studies HED applications. In particular, we present comparisons with recent ICF-relevant experiments investigating plasma interpenetration in a hohlraum surrogates [3] and nonlocal electron heat conduction in laser-produced coronae [4]. |
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TP11.00091: Deep-Learning-Based Predictive Models for Laser Direct Drive at the Omega Laser Facility Rahman Ejaz, Varchas Gopalaswamy, Riccardo Betti The physics of inertial confinement fusion is rich and complex. Simulation codes that are used to design experiments are computationally expensive and lack the predictive capability required for extensive parameter exploration in search of a high-performing design for laser direct drive. In this work we use deep learning to build a fast emulator of experiments. To facilitate the development of the deep-learning model, an autoencoder is used to reduce the dimensionality of the input space. Two deep learning models are developed. One model is trained on a vast array of simulation data and is subsequently calibrated to expensive and limited experimental data using a technique known as “transfer learning.”[1] The other model is trained on a statistical model[2] and is subsequently calibrated using experimental data. A comparative study of the two predictive models is carried out. The models reproduce key experimental observables with high accuracy. Inference times on the DNN[JO1] models are unprecedented relative to the run time of simulation codes. The DNN models facilitate rapid exploration of a high dimensional input parameter space. Once high-performing designs are identified, high-fidelity simulations are used to understand the key physics of the design. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. [1] K. D. Humbird et al., IEEE Trans. Plasma Sci. 48, 61 (2020).
[2] V. Gopalaswamy et al., Nature 565, 581 (2019).
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TP11.00092: Efficient kinetic simulations in the Z inner MITL Evstati G Evstatiev, Mark H Hess The Z inner magnetically insulated transmission line (MITL) |
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TP11.00093: Using Deep Learning to Investigate Performance and Variability in Inertial Confinement Fusion Experiments Michael Pokornik, Jim A Gaffney, Shahab F Khan, Brian J MacGowan On August 8th, 2021 an inertial confinement fusion (ICF) experiment (N210808) at the National Ignition Facility (NIF) achieved a record-breaking fusion yield of 1.35 Megajoules. Follow up shots, investigating the sensitivity of N210808 implosion performance to engineering and design variability, demonstrated the importance of designing robust experiments. |
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TP11.00094: Hybrid-kinetic PIC modeling of fusion reactions in high-density laser-driven p-B11 plasmas Carsten H Thoma, Dale R Welch, Thomas A Mehlhorn, Igor E Golovkin The B11(p,α)αα fusion reaction is an attractive option for energy production due its aneutronic character [1]. But a purely thermonuclear approach appears to be prohibitive due to low reactivity of p-B11 fuels compared to conventional fusion reactions. A path to developing a high-gain p-B11 target will likely need to incorporate a fast-ignition-like approach to achieving burn, with high-energy protons accelerated by intense laser pulses interacting with a pre-compressed fuel. In order to determine possible burn regimes in such a configuration, it is important to model kinetic effects of the accelerated protons and resulting fusion products as well as account for loss mechanisms. For this purpose, the hybrid PIC code Chicago is utilized as a simulation tool which has binary coulombic collisions to include the effect of up-scattering of protons by alphas. Fusion reactions are also performed in a fully-binary fashion, and utilize the latest cross-section data for the p-B11 reaction. A radiation model using tabulated opacities is used to account for bremsstrahlung losses. Chicago can also be used to directly model laser-plasma interactions. We present the results of simulations of pitcher-catcher experiments performed at the Texas PW laser facility, in which simulations correctly predict alpha-particle production, and a preliminary survey of the burn-space of a potential p-B11 target. |
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TP11.00095: LASER PLASMA INTERACTIONS Session Chairs: |
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TP11.00096: Electron collisions with laser speckles Mark Sherlock, Pierre A Michel We show that the ponderomotive force and electric field associated with laser speckles can scatter electrons in a laser-produced plasma in a manner similar to Coulomb scattering. Analytic expressions for the effective collision rates are given and verified with numerical simulations of particles interacting with speckled lasers. The electron-speckle collisions become important in low-Z plasmas and at high laser intensity or during filamentation, affecting both the long- and short- pulse regimes. As an example, we find the effective collision rate in the laser-overlap region of hohlraums on the National Ignition Facility is expected to exceed the Coulomb collision rate by an order of magnitude, leading to a fundamental change to the electron transport properties in the presence of intense lasers. At high intensities (>1018Wcm2) the scattering is fast enough to cause direct absorption of laser energy. |
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TP11.00097: Mitigation of cross-beam energy transfer in inhomogeneous plasmas through increased laser bandwidth Alexander Seaton, Lin Yin, Russell K Follett, Ari Le, Brian J Albright We recently examined the efficacy of enhanced laser bandwidth for mitigation of cross-beam energy transfer (CBET) via a combination of linear theory and simulation[1,2]. Our theoretical results demonstrated that, in the linear regime, bandwidth is effective at mitigating CBET for bandwidths exceeding the ion-acoustic wave (IAW) frequency. These results were verified by simulation, and we showed that nonlinear effects may lead to deviations from the linear scaling. However, these simulations were of homogeneous plasmas, whereas under direct laser-drive conditions the plasma includes significant density and velocity inhomogeneity. We now present results from an extended study in which we incorporate plasma inhomogeneity. We demonstrate that bandwidth remains effective at suppressing CBET in the linear regime, and show results from simulations investigating the impact of nonlinear effects. |
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TP11.00098: Coupling nonlinear CBET effects to radiation-hydrodynamic modeling of ICF/HED experiments via laser ray tracing Lauren Green, Lin Yin, David J Stark, Luis Chacon, Brian M Haines, Guangye Chen CBET is an important energy redistribution mechanism in direct drive and indirect drive ICF/HED experiments performed on large-scale laser facilities. In order to model these experiments accurately, it is essential to include feedback from the laser-plasma instabilities on hydrodynamics. Nonlinear effects can cause CBET gain to deviate from linear theory predictions typically used in laser ray tracing codes. In this work, we developed a new CBET formulation in Mazinisin [1], a laser ray-tracing code developed by LLE, that includes effects of saturation in a physics-based nonlinear model and evolving plasma conditions from simulations using the LANL Eulerian radiation hydrodynamics code xRAGE. We performed simulations to test the implementation of the nonlinear CBET model using settings and results from experiments [2] at the LLE OMEGA laser facility. These experiments observe CBET saturation due to ion heating, which is not represented in a time-dependent manner by the linear model alone. We will compare results from linear and nonlinear CBET models and discuss the conditions necessary for improving the agreement between simulations and experiments. LA-UR-22-25814 |
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TP11.00099: Nonlinear Models for Coupling the Effects of Stimulated Raman Scattering to Inertial Confinement Fusion Codes David Stark, Lin Yin, Truong Nguyen, Guangye Chen, Luis Chacon, Lauren Green, Brian M Haines Laser plasma instabilities reduce driver-target coupling and are fundamental limiters of fusion performance for inertial confinement fusion (ICF). Being able to predict and model LPI effects is important for the success of ICF. We present VPIC particle-in-cell simulations of multi-speckled laser beams undergoing stimulated Raman scattering (SRS) at various densities and intensities relevant to indirectly-driven ICF systems. Based on the wavenumber of the SRS daughter electron plasma wave, regions with underpinning SRS saturation physics are identified: Electron-trapping dominated region with intermediate klD values, strong damping region at larger klD values, and region with the presence of Langmuir decay instability at lower klD values. We developed a nonlinear SRS reflectivity model that reflects the base scaling (klD)-4 and its modifications. Electron trapping manifests in the electron distribution functions, and we have developed a new ????-Gaussian-mixture algorithm enabling an accurate characterization of the trapped particle population. Together with this SRS hot electron description, VPIC simulations are used to develop a nonlinear energy deposition model and a hot electron source model based on the Manley-Rowe relations to couple SRS effects to a high-fidelity electromagnetic ICF design code. |
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TP11.00100: Nonlinear cross-beam energy transfer model for ICF/HED design codes Lin Yin, Truong Nguyen, Guangye Chen, Luis Chacon, David J Stark, Lauren Green, Brian M Haines Cross-beam energy transfer (CBET) allows crossing laser beams to exchange energy and is critically important for ICF/HED experiments. The nonlinear physics of CBET for multi-speckled laser beams is examined using particle-in-cell simulations for a range of plasma conditions, laser intensities, and crossing angles relevant to indirect-drive ICF experiments. |
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TP11.00101: Focusability in the multi-pump laser pulse amplification in plasma Kirill Lezhnin, Kenan Qu, Nathaniel Fisch Spatially combining multiple strong laser beams is a promising concept for achieving ultrahigh laser intensities. Proof-of-principle experiments have been conducted at the National Ignition Facility to report a combination of up to twenty pulses with high energy conversion efficiency [1]. However, the combination process could reduce the seed focusability due to the mismatch of the seed and pump wavefronts. Here, we investigate the effect of the finite pump beam size on the focusability of the seed pulse. We propose an approach to retain and even improve the seed focusability by specifically arranging multiple pump beams. The results are demonstrated by numerical solution of coupled nonlinear Schrodinger equations and 2D particle-in-cell simulations. |
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TP11.00102: A Photon Kinetic Description of Laser Bandwidth Mitigation of Laser Plasma Interactions Robert Bingham, Raoul M Trines, Luis O Silva In both direct and indirect drive laser fusion it is necessary to limit the level of stimulated scattering from laser plasma interactions to almost zero level. One way to accomplish this is to use broadband lasers. However, the inclusion of bandwidth or incoherence effects in theoretical models of laser driven parametric instabilities in plasmas is a long-standing problem. A generalized Wigner Moyal statistical theory of radiation, or generalized photon kinetics (GPK), formally equivalent to the full wave equation, is used to derive the general dispersion relation for Stimulated Raman Scattering (SRS) and Stimulated Brillouin Scattering (SBS) driven by a spatially stationary radiation field with arbitrary statistics. Both three-wave processes and four wave processes are included, and for a plane-wave pump field the standard results are recovered. Analytical results are derived for different regimes of SRS and SBS and wave number ranges, showing universal lowering of the growth rate with bandwidth. Laser bandwidths of around a percent can reduce the growth rates significantly to a level where the level of stimulated scattering is acceptable. Such photon statistical models can also be used to study other problems such as photon Landau damping and photon acceleration in plasmas. |
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TP11.00103: LPI Mitigation Studies Via Laser Bandwidth at the Nike Laser Facility* James L Weaver, Jaechul Oh, Jason W Bates, Stephen P Obenschain, David M Kehne, Andrew J Schmitt, Russell K Follett Increased laser bandwidth is currently of great interest as a means to mitigate laser plasma instabilities (LPI) in plasmas relevant to inertial confinement fusion. The output spectrum for the Nike laser (lpeak=248.5 nm) can be controlled by etalons in the front end over a range of (0.3-3 THz). This range is suitable for the investigation of bandwidth effects on slower growing instabilities such as stimulated Brillouin scattering (SBS) and cross-beam energy transport (CBET). A previous LPI campaign at Nike used a single type of low density foam target to produce large volume plasmas with estimated 5-10x longer density and velocity scale-lengths than solid CH targets. The current study explores SBS and CBET over a wider range of initial foam densities and utilizes exploding foil targets for comparison to LPI experiments from longer wavelength laser systems. Possible application of stimulated rotational Raman scattering (SRRS)[Weaver, et al. Applied Optics 2017] for broader bandwidth (> 3 THz) experiments will also be discussed. |
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TP11.00104: Hydrodynamic shocks produced by the ICF scale laser beams in flowing, underdense plasmas. Wojciech Rozmus, Joshua Ludwig, Stefan Huller, Harvey A Rose, Avram Milder, Paul-Edouard Masson-Laborde, William A Farmer, George F Swadling, Bradley B Pollock, Colin ruulsema, Pierre A Michel High energy randomized laser beams interacting with flowing plasmas can produce a plasma response that leads to beam bending and, by momentum conservation, to slowing down of the plasma flow velocity [1]. For the incoming plasma flow, with a velocity slightly greater than sound speed, the plasma response to a ponderomotive force exerted by speckled laser beams is the strongest, such that slowing down of the flow to subsonic velocities leads to the formation of a shock. Using hydrodynamic simulations and the scaling laws we will discuss designs of experiments on NIF and OMEGA facilities that will demonstrate bow shock formation and allow to verify theoretical predictions. Simulations have shown large density and velocity jumps for the LEH parameters on NIF. The necessary condition for the shock to be formed is the presence of the sonic velocity in the transverse flow across the laser beam. We will specify the required power and size of the interacting beams. Interaction of the expanding gold plasma in a hohlraum glint experiment will be examined for the shock generation. |
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TP11.00105: Laser scatter and re-scatter near the quarter critical surface Frank S Tsung, Benjamin J Winjum, SJ Spencer, Roman Lee, Warren B Mori Under IFE relevant conditions, the high frequency hybrid instability where the backward going daughter wave can contain an electromagnetic component. Under these conditions, the scattered lights from the quarter-critical surface can themselves undergo re-scatter down near its own quarter critical surface. Going down the gradient, the laser encounters the quarter critical surface first and therefore the HFHI instability takes on an even bigger role under these conditions. Using 2D and 3D particle-in-cell simulations, we will investigate the scatter and re-scatter of laser near the quarter critical surface under IFE relevant conditions, and demonstrate the importance of these instabilities in current and future experiments. |
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TP11.00106: Measurements of the effects of an external B-field on backscattered Stimulated Raman Scattering(SRS) reflectivity Alemayehu Bogale, Mathieu Bailly-Grandvaux, Simon Bolanos, Mario Manuel, Benjamin J Winjum, Chris A Walsh, Jacob Saret, Roman Lee, Frank S Tsung, Warren B Mori, Dustin Froula, Timothy Filkins, Farhat N Beg
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TP11.00107: Accounting for speckle scale beam-bending in classical ray tracing schemes for propagating realistic pulses in indirect drive ignition conditions Charles Ruyer, Pascal P Loiseau, Gilles Riazuello, Raphael Riquier, Arnaud Debayle, Paul-Edouard Masson-Laborde We propose a semi-analytical modeling of smoothed laser beams deviation induced by plasma flows. Based on a Gaussian description of speckles [1,2], the model includes spatial, temporal and polarization smoothing techniques, through fits issued from hydrodynamic simulations with a paraxial description of electromagnetic waves. This beam bending model is then included in a ray tracing algorithm, and carefully validated. When applied as a post-process to the propagation of the inner cone in a full-scale simulation of a NIF experiment, the beam bending along the path of the laser affects the refraction conditions inside the hohlraum and the energy deposition, and could explain the anomalous refraction measurements, the so-called glint observed in some NIF experiments [3]. We will finally discuss about possible inline implementation strategies. |
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TP11.00108: FUND: COMPUTATION
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TP11.00109: The PlasmaPy Project: Building an Open Source Software Ecosystem for Plasma Science Nicholas Murphy, Erik Everson, Dominik Stańczak, Peter V Heuer, Haman Bagherianlemraski, Shane Brown, Khalil J Bryant, Tiger Du, Rajagopalan Gangadharan, Elliott Johnson, Ritiek Malhotra, Bennett Maruca, Ramiz Qudsi, David A Schaffner, Stephen T Vincena The mission of the PlasmaPy project is to foster the creation of a fully open source Python ecosystem for plasma research and education. The PlasmaPy package is being developed to include the common core functionality needed by plasma physicists across disciplines. PlasmaPy prioritizes code readability, consistency, and maintainability while using best practices for scientific computing such as open development, version control, continuous integration testing, and code review. We will describe PlasmaPy's current capabilities, and describe new capabilities related to dispersion relation solvers, Thomson scattering, and magnetic topology. We will present code development plans for the next year, describe how PlasmaPy 0.7.0 was launched into space, and discuss how anyone in the community is welcome to contribute to the project. |
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TP11.00110: Conservative Finite Element Approach to Magnetized Plasma Simulation Ilon Joseph, Alejandro Campos, Milan Holec, Chris J Vogl, Ben Zhu, Andris M Dimits, Benjamin Dudson, Tzanio Kolev, Mark L Stowell, Ben S Southworth The physics of 2D drift-reduced MHD models, including generalizations of the Hasegawa-Mima and Hasegawa-Wakatani models are explored using a new finite element approach to magnetized plasma simulation and compared to results of the GDB finite difference code. These models are implemented using MFEM, a highly scalable finite element library, that can address the challenging physical, geometric, and numerical issues associated with edge plasmas. Recently, we derived and implemented [1] arbitrary polynomial-order finite element spatial discretizations for the drift-reduced magnetohydrodynamics (MHD) equations that conserve both energy and enstrophy to machine precision when coupled with generally symplectic time-integration methods. However, we discovered that the fully conservative model is not accurate at long times and that dissipation must be reintroduced to control the short wavelength part of the spectrum. We found that using an upwinded DG formulation, which dissipates enstrophy while conserving energy, is the most efficient method for generating accurate results for a suite of 2D turbulence test problems. We are extending these results to 3D incompressible MHD and plasma turbulence. |
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TP11.00111: Simulating quantum light in plasmas using programmable qubits Yuan Shi, Vinay Tripathi, Bram Evert, Yujin Cho, Amy F Brown, Max D Porter, Xian Wu, Vasily I Geyko, Alexander D Hill, Christina Young, Eyob A Sete, Ilon Joseph, Daniel A Lidar, Jonathan L DuBois, Matthew Reagor Light-plasma interactions are usually explored in the classical limit of laser light, which is a coherent state of photons. However, photons can occupy intrinsically quantum states, such as squeezed states, that are expensive to simulate using classical computers. Here, we develop a quantum model of plasma-mediated light amplification and demonstrate a two-qubit simulation on quantum hardware. Using the best-performing qubits, we show that the exact unitary, which maps initial to final states, can be realized to high fidelity. However, error mitigation is required before the quantum device can be used to simulate beyond a few time steps. We employ random compilation to suppress coherent error accumulation, such that each time step uses a different but equivalent gate sequence. Moreover, to account for decoherence, we rescale the exponentially decaying probability amplitudes using rates measured from randomized benchmarking. Finally, we reduce gate depth by merging single-qubit gates using optimal control and reducing two-qubit gate pulse duration using parametric entanglers. Using these techniques with readout error mitigation, present-day quantum hardware can advance enough time steps to capture interesting nonlinear dynamics. |
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TP11.00112: Hierarchical, Multimodel, Multiscale Parallel-In-Time Paul Tranquilli, Lee Ricketson, Terry Haut, Jeffrey A Hittinger Kinetic plasma simulations must reckon with many widely varying time-scales, and thus are routinely stability-limited and take many thousands of time-steps. While this makes parallel-in-time (PIT) methods appealing, the spatiotemporal coarsening required by standard PIT schemes can lead to iterations that bear little resemblance to the physical solution — or may even be unstable — thus slowing convergence and limiting speed-ups. We thus present a parallel-in-time strategy that employs a coarsening of models, rather than meshes, to accelerate time-to-solution for high-dimensional kinetic plasma models by leveraging their much cheaper, lower dimensional fluid approximations. The method is tested, with promising initial results, on the two-stream instability. |
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TP11.00113: Curved Mesh and Adaptive Mesh Refinement Strategies for Strong Magnetic Anisotropy Ilon Joseph, Chris J Vogl, Milan Holec, Ben S Southworth, Alejandro Campos, Andris M Dimits, Tzanio Kolev, Ketan Mittal, Ben Zhu Transport in magnetized edge plasma along the magnetic field lines is many orders of magnitude stronger than transport perpendicular to the field lines. As a result, the drift-reduced (extended) magnetohydrodynamics approach used to model the plasma results in operators that are highly anisotropic and in sharp boundary layers where the magnetic field topology changes, such as at the magnetic separatrix in a tokamak. Approximation theory results show that mesh elements must be smaller than the boundary layer width to properly resolve the solution in the layer, regardless of the order of finite element function space used. Thus, uniform mesh approaches quickly become unusable for the sharp layers in realistic anisotropy regimes. Instead, this work leverages the high-order curved mesh and adaptive mesh refinement capabilities of the MFEM finite element library to make simulating edge plasma in realistic anisotropy regimes more tractable. Curved meshes can conform the mesh edges to magnetic field lines in realistic tokamak geometry, enabling elements thin enough in the perpendicular direction to resolve the layer yet elongated enough in the parallel direction to reduce the problem size. Adaptive mesh refinement can systematically improve accuracy within and around boundary layers, especially when the location of layers is not predictable. The significant improvement in accuracy, given a fixed computational cost, provided by both curved meshes and adaptive mesh refinement is presented for simplified tokamak magnetic field geometries. |
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TP11.00114: Control variate hybrid particle-in-cell method with exact energy conservation Joshua W Burby, Adam J Stanier, Luis Chacon, Guangye Chen Kinetic plasma simulations based on the particle-in-cell (PIC) technique routinely employ control variates to reduce deleterious marker particle noise in fluid moment computations. However, when using the standard delta-f technique, noise reduction comes at the cost of unphysical total energy errors. We will report on a new approach to the delta-f PIC method in the context of a collisionless hybrid fluid electron - kinetic ion system that preserves total energy exactly. To achieve exact conservation, the method is deduced from a continuous-time particle discretization that modifies the electron pressure evolution equation with small, low-noise counterterms. Time is then discretized using a skew-gradient method. Notably, the scheme conserves the variance-reduced total energy, and not the standard full-f energy expression. |
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TP11.00115: Implementing Distributed-Weight Particle Loading for BARS with PIC Codes Sean M Finnegan, Bedros B Afeyan, Luis Chacon, David J Bernstein To implement the mini-BARS algorithm [1] for improved sampling of velocity-partitioned phase space, we use a methodology for generating mixed-Maxwellian-weighted electron velocity distribution functions (VDF) as initial conditions. We test these methods on kinetic, nonlinear initial value plasma waves. We show how to down-sample from a master VDF (e.g. ≥108 particles) so that low order moments are conserved as is entropy per velocity partition. From many samples those with the least pathological features are selected. Some advantages of this approach are observed over traditional PIC sampling, including the so called quiet start or random sampling strategy that Monte Carlo techniques such as PIC most naturally adhere to. This work is performed using the versatile and sophisticated LANL DPIC code [2] together with mini-BARS. |
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TP11.00116: Hybrid-VPIC Code and Applications Ari Le, Lin Yin, Adam J Stanier, Blake A Wetherton, Brett Keenan, Dan Winske, Misa Cowee, Fan Guo, Qile Zhang, Scott V Luedtke, William S Daughton, Brian J Albright, Li-jen Chen, Cary B Forest, Jan Egedal, Douglass Endrizzi, Chuanfei Dong, Liang Wang Hybrid-VPIC is built on the high-performance particle-in-cell code VPIC [1]. It combines a massless fluid electron model with a kinetic PIC ion model, allowing simulations of much larger systems where ion kinetics are important but the electrons are fluid-like. In addition to a standard explicit hybrid PIC algorithm, Hybrid-VPIC includes models for Coulomb collisions between particle ions and the electron fluid [2], fusion burn, electron heat transport in collisional multi-ion plasmas [3], and various open boundary conditions. Example applications include: interfacial mix in HED settings driven by ambipolar diffusion or by hydrodynamic instabilities; electromagnetic instabilities upstream of planetary shocks; the global dayside magnetopshere of Mercury; particle acceleration during magnetic reconnection; ionized debris transport after the 1962 Starfish high-altitude nuclear test; and interchange modes in magnetic mirror fusion devices. (LA-UR-22-25935) |
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TP11.00117: A multiscale hybrid Monte-Carlo-Gaussian Coulomb-Collision Algorithm for Hybrid Kinetic-Fluid Simulations Guangye Chen, Luis Chacon, Adam J Stanier, Bobby Philip, Steven Anderson Coulomb collisions in particle simulations for weakly coupled plasmas are typically modeled by Monte-Carlo (MC) methods [1]. One of the main disadvantages of MC is the timestep accuracy constraint γ△t<<1 to resolve the collision frequency γ [2]. The constraint becomes extremely stringent for self-collisions in the presence of high-Z species, and for interspecies collisions with large mass disparities, rendering such simulations impractical. To overcome these difficulties, we explore a hybrid MC-Gaussian model for hybrid kinetic-fluid simulations. Specifically, we devise a collisional algorithm that leverages Maxwellians (i.e. isotropic Gaussians) [3] for both highly collisional kinetic species and fluid ones. We perform Gaussian-particle collisions using the Lemons method [4], which we have improved by more careful treatment of low-relative-speed particles. We extend the standard MC method [1] for particle-particle collisions with a new variable-particle-weight-pairing scheme without losing conservation properties. The new hybrid MC-Gaussian method is strictly conservative and is orders of magnitude faster than straight MC. We will illustrate the accuracy and performance of the proposed method with several examples of varying complexity, including relaxation of species with disparate charges and masses, and transport problems with kinetic-ion-fluid-electron hybrid simulations. |
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TP11.00118: Meshfree particle model for kinetic plasma simulations John M Finn, Evstati G Evstatiev We revisit a meshfree particle model for kinetics of a 1D electrostatic |
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TP11.00119: Can Current Quantum Algorithms Speed Up Linear Vlasov Equation Simulations? Abtin Ameri, Paola Cappellaro, Hari K Krovi, Nuno F Loureiro Plasma physics is notoriously difficult to simulate. It is natural to seek alternative computational platforms that may offer speedups of such simulations. Quantum computers are an attractive option, as they have the potential to solve certain problems exponentially or polynomially faster than classical computers (Grover 1996, Shor 1999). Previous work in this area has focused on the collisionless, linearized Vlasov equation, and has claimed an exponential speedup with respect to system size (Engel, Smith, and Parker 2019). This is done by truncating the velocity space and recasting the linearized Vlasov equation as a Schrodinger-type equation, for which Hamiltonian simulation algorithms can be used (Low and Chuang 2019). We show that by expanding in velocity space using Hermite polynomials, we can solve the same problem using an exponentially smaller system, thereby yielding a classical algorithm with the same performance as the proposed quantum algorithm. We also discuss that it is unlikely that a quantum version of our classical algorithm can yield an exponential speed up, but it is likely that we can obtain polynomial speedup in some parameter regimes. It is also straightforward to add collisions to our system without changing the performance of the algorithm. |
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TP11.00120: Bracket Structure for Gyrokinetic Theory Bruce D Scott The Lagrangian for the gyrokinetic description of magnetised plasma |
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TP11.00121: A 1-dimensional electrostatic plasma model for testing kinetic theory validity Philip J Morrison, Francesco Pegoraro A starting point for deriving the Vlasov equation with a collision operator is the BBGKY hierarchy that describes the dynamics of coupled marginal distribution functions. With a large plasma parameter (number of particles in a Debye sphere) one justifies dropping certain correlations and makes assumptions so as to eliminate 2-point correlations in terms of the 1-point function. Prior to making the assumptions that lead to the Vlasov equation with the Landau-Lenard-Balescu collision operator, there exists a closure that is a Hamiltonian field theory for the coupled dynamics of the 1-point and 2-point functions [J. Marsden, P. Morrison, and A. Weinstein, Cont. Math. 28, 115 (1984)], whence the Vlasov-Landau-Lenard-Balescu (VLLB) theory can be derived. Because of the curse of dimensions, numerically testing the assumptions of the VLLB theory is prohibitive. In this poster, we will present a 1-dimensional Hamiltonian model composed of interacting aligned charged disks in order to address the validity of the Bogoliubov assumption on the decay of correlations, a basic premise of plasma kinetic theory. |
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TP11.00122: Accelerating Ensembles of Plasma Kinetic Simulations through Adaptive Learning: NSCAR, BARS, mini-BARS, TPOR and all that Bedros B Afeyan, Sean M Finnegan, Luis Chacon We will describe elements of NSCAR: Nearby Skeleton Constrained Accelerated Recomputing and its proginy BARS, mini-BARS and TPOR. Nearby solutions are compressed and added as a variational constraint on the overall Lagrangian formulation of the Kinetic modeling problem. The constraints force the search for solutions to favor proximity to the previously obtained solutions. BARS stands for Bidirectional Adaptive Reduction Scheme. This adaptively resampled phase-space algorithm that traverse forwards and backwards in time enables new variational optimization that benefits ensembles of simulations. The key is to use similar patches in phase space to provide excellent initial guesses for optimum computational performance in nearby parameter space. This way, what is learned with O(4x) overhead in one simulation is shared between nearby runs and becomes essentially free. A simplified version of BARS, called mini-BARS, has been used together with the PIC code DPIC to study ponderomotively driven electron plasma waves and KEEN waves with velocity-partitioned phase space (with variable-width velocity strips not general patches in phase space) and found to accelerate computations by a factor of O(100), at very low overhead cost (roughly 4x). The winning strategy is to learn how to over-sample the tail and undersample the bulk of the velocity distribution function adaptively. |
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TP11.00123: Generalizing the Yee Algorithm to Higher Order on an Unstructured Mesh Alexander S Glasser, Hong Qin It is well known that the Yee algorithm satisfies two crucial properties: (i) It faithfully preserves the geometric structure of Maxwell's equations, ensuring its accuracy in long-time numerical simulations; and (ii) its calculations are local and therefore parallelizable, enabling Yee's method to capitalize on the speed and scalability of high-performance computing architecture. In this work, Yee's algorithm is recast in the formalism of finite element exterior calculus and, in contrast with its usual finite-difference interpretation, it is thereby viewed as a low order finite element method with simplified mass matrices. Previous attempts to improve upon Yee's method with finite elements have sacrificed the indispensable computational efficiency afforded by its localness. Here, we leverage the finite element point of view to generalize the Yee algorithm to higher order and general meshes, while developing innovative techniques to maintain its geometric naturalness, physically-motivated localness, and parallel efficiency, nevertheless. |
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TP11.00124: Benchmarks of a conservative spectral solver for the nonlinear Boltzmann transport equation. George J Wilkie The Boltzmann equation provides the theoretical foundation for plasma physics and aerodynamics, while also appearing across physics in semi-classical contexts. While Monte Carlo techniques have been a robust and mainstream method, difficulties arise when coupled to deterministic fluid and kinetic plasma simulations. Spectral methods also have a long history of being applied to the Boltzmann equation, and recently a Galerkin-Petrov method has been found which is manifestly conservative for the full bilinear collision operator [Gamba & Rjasanow, JCP 2018]. LightningBoltz is an implementation of this algorithm, extended for inelastic collisions, tabulated cross sections, implicit time advance, and adaptive integration techniques. A key feature is the precomputation and online storage of the discrete collision operators, which allows users to solve the transient 1D+3V Boltzmann equation with remarkable efficiency. Several benchmarks across a range of disciplines are presented. Firstly, the artificial constructed solution with Maxwell molecules is shown (including inelastic processes). Next, the collisional Chapman-Enskog predictions for viscocity and thermal diffusivity are reproduced to high accuracy at small Knudsen number. Cross-code comparisons are shown to accurately reproduce the results of: BOLSIG+ for electrons in weakly ionized plasma, and DEGAS2 for neutrals in a 1D scrape-off-layer-like domain. Limitations of the spectral representation are also discussed, and several methods for generalizing the algorithm for broad energy scales will be discussed. |
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TP11.00125: In Computational Physics, Machine Learning Research is a Speculative Bubble Nicholas B McGreivy, Ammar Hakim In recent years, there has been a massive growth in the number of papers published that apply machine learning (ML) to computational physics. Some highly cited papers have shown, allegedly, that machine learning can dramatically accelerate the solution of PDEs. Given the number of papers being published and the success of these papers, it would be reasonable to conclude that ML is becoming a standard tool in computational physics. This narrative -- that machine learning is causing rapid progress in computational physics -- is, as we will argue, wrong. Instead, we will argue that within computational physics, ML research is a speculative bubble. We believe that a failure of ML papers to consider state-of-the-art baselines is the primary cause of this speculative bubble and the evidence that it exists. The extraordinary versatility of machine learning has made it easy to forget that versatility does not imply utility. For machine learning to have utility, it must beat state-of-the-art baselines. As we will show, all of the most impressive results and most highly cited papers either use a baseline which is not state-of-the-art, or they fail to compare to a baseline at all. As a result, readers are misled into believing that machine learning has been much more successful than it really is. |
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TP11.00126: Algorithms for electron dynamics in a Lorentz plasma – a case study of algorithmic plasma physics Hong Qin, Yichen Fu, Alexander S Glasser, Eric Palmerduca Standard algorithms, such as the RK4, symplectic RK4, and Euler-Maruyama, have been developed for solving generic deterministic and stochastic differential equations. However, these methods are not most suitable for applications in plasma physics. Using the example of electron dynamics in a Lorentz plasma, we demonstrate that it is necessary to develop custom structure-preserving geometric algorithms that preserve the symmetries and conservation laws specific to the system, including space-time symmetry and energy-momentum conservation, covariance, gauge symmetry, and symplecticity. These desirable features ensure the accuracy in physics generated by the algorithms, but also limit their applicability as general algorithms for generic differential equations. These bespoke algorithms belong to plasma physics. They make up a subset of plasma physics that can be appropriately called algorithmic plasma physics. The proposition that plasma physics has intrinsic algorithmic components should not be surprising. For example, to model the physics of electron pitch angle scattering, the governing stochastic differential equation cannot be correctly formulated without choosing an algorithm first, be it the Ito integral, Stratonovich integral, or others. |
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TP11.00127: Validation and benchmarking of 3d particle-in-cell simulations using multi-device architecture in the Vorpal code Steven Lanham, Jarrod Leddy, Scott W Sides, John R Cary The Vorpal code allows for the simulation of plasmas over a wide variety of conditions, typically solving for the plasma dynamics using particle-in-cell (PIC) and coupled electromagnetics solutions [1]. Recent improvements have been made to flexibly utilize heterogeneous architectures - from many CPUs to many GPUs, or a mixture of both. Computation on GPUs is most effective when algorithms are single-instruction multiple-data, so efficient computing of the entire PIC cycle can be challenging and often problem-dependent. Validation of the updated code was done by comparing simulation results to generally known, standardized test cases [2]. Performance benchmarking of the full PIC cycle was done for various architectures, efficiency and potential bottlenecks will be discussed. |
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TP11.00128: Dual PIC: A Geometric PIC discretization of Lie-Poisson brackets William Barham, Yaman Güçlü, Philip J Morrison, Eric Sonnendrücker Virtually all non-dissipative models in plasma physics, from the Liouville equations and the BBGKY hierarchy to various kinetic and fluid models, have been shown to possess a Lie-Poisson structure when modeled as noncanonical Hamiltonian systems. In discretizing such brackets, one encounters a closure problem. That is, given a finite representation of the fields, it is usually not the case that the dynamic evolution of those fields is prescribed only in terms of that finite dataset. Particle based representations circumvent this difficulty with relative ease, but typically suffer from limited accuracy and difficulties in coupling to grid-based variables. We present the "dual PIC" method for the Vlasov-Poisson system. This method makes explicit use of two different representations of the phase space density: a particle based discretization and a Galerkin representation. The two representations are related to each other through an L2 projection. Moreover, the error in this L2 projection is conserved as a Casimir invariant of the flow. While we present the method in the context of Vlasov-Poisson, the strategy holds promise for application to general Lie-Poisson brackets. |
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TP11.00129: Mapping classical nonlinear plasma dynamics to mean-field theory approximations of many-body quantum systems Alexander Engel, Graeme Smith, Scott E Parker Mean-field theory can be applied to approximate various quantum systems in the limit of many quantum particles. For example, the Gross–Pitaevskii equation approximates the dynamics of a system of many interacting bosons with a nonlinear partial differential equation for a single-particle wavefunction. Conversely, by considering the reverse of mean-field mappings, nonlinear dynamical systems including some classical plasma systems can be associated with many-body quantum systems. Simulating these many-body quantum systems on a quantum computer could allow for approximations to nonlinear plasma dynamics with significantly different computational complexity than classical simulation methods. Whether a quantum speedup is possible depends on how many quantum particles are needed to approximate the desired output quantity. We investigate this question theoretically and numerically. Output quantities must be well behaved in order to be approximated with only a small number of quantum particles. We also consider the inclusion of measurements into the quantum dynamics as a strategy for improving the approximation of the nonlinear mean-field dynamics. |
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TP11.00130: Hydrodynamics of Void Collapse Kelin Kurzer-Ogul, David S Montgomery, Brian M Haines, Arianna Gleason, Hussein Aluie, Jessica Shang Voids are low-density regions in an otherwise homogeneous higher-density medium. The hydrodynamics of a collapsing void are important across a wide range of physics, including planetary science, astrophysics, nuclear fusion, and materials science. In the high energy density regime, instabilities generated by collapsing voids are a major challenge in the pursuit of fusion ignition. Void collapse is highly non-linear, involving shock reflection, refraction and focusing which results in the formation of plasma jets and phase transformation in the surrounding material. Experiments imaging the shock-induced collapse of voids are underway, but are constrained by spatial and temporal resolution. In this study, we use xRAGE, a Los Alamos National Laboratory radiation-hydrodynamic code, to understand the evolution of a collapsing void by revealing dynamics at timescales shorter than experimental imaging framerates. These simulations reveal separation and acceleration of the shock front as it transits the void, creating an inward pressure gradient in its wake which leads to the development of instabilities at the former void's edge. |
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TP11.00131: A Hamiltonian structure preserving discretization of Maxwell's equations with general constitutive laws William Barham, Yaman Güçlü, Philip J Morrison, Eric Sonnendrücker It is frequently advantageous to characterize the microscopic response of a medium to an electromagnetic field with constitutive relations for the polarization and magnetization of that medium which self-consistently depend on the fields. This basic idea accounts for the electromagnetic component of many reduced models in plasma physics and nonlinear optics. It is possible to describe such models in a general Hamiltonian framework. We consider a Hamiltonian structure preserving spatial discretization of Maxwell's equations in general media using a spectral element finite element exterior calculus method. This method is capable of supporting arbitrary (and even nonlinear) constitutive laws. When the spatially discretized model is time evolved using a Hamiltonian splitting method, the energy is approximately conserved, and Gauss's laws for the electric and magnetic fields are exactly conserved. Moreover, because of its Hamiltonian structure preservation, it is well suited to be used as the field solver in a PIC scheme. |
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TP11.00132: Dynamical low-rank methods for capturing kinetic effects in the collisional transition regime Jack Coughlin, Jingwei Hu, Uri Shumlak Kinetic equations such as the Boltzmann-Maxwell system describe plasma behavior |
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TP11.00133: An adaptive domain-hybridized plasma fluid model Andrew Ho, Uri Shumlak Plasma models have regimes of validity that depend on the local parameters. |
Author not Attending |
TP11.00134: Data-driven reduced-order modeling of nonlinear MHD systems Sina Taheri, Christopher J Hansen, Steven L Brunton, Alan Kaptanoglu Magnetized plasmas are highly complex, multi-scale systems and understanding their nonlinear dynamics traditionally requires high-resolution first-principles models which are numerically extensive. Fortunately, emerging data-driven techniques can be leveraged to develop interpretable reduced-order models of these highly nonlinear systems. The sparse identification of nonlinear dynamics (SINDy) algorithm [1] is one such method that identifies a minimal dynamical system model. In this work, we use projection-based model reduction [2] for an MHD system where energy and helicity are injected using time-invariant electric and magnetic fields on the top surface of a perfectly conducting cylinder, driving a saturated state that is sustained by periodic bursts of nonlinear dynamo activity. Then, we use the PySINDy package to build low-order sparse models to accurately describe the nonlinear dynamics of the system. |
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TP11.00135: Validation of a reacting three-fluid 5-moment model for THz breakdown W. R Thomas, Eric T Meier, Uri Shumlak High powered THz waves have potential applications in scanning, remote sensing, and high-data rate communication. At sufficiently high power ionization of the surrounding gas is inevitable, leading to absorption, refraction, and reflection of the THz waves. Understanding the plasma's formation, as well its interaction with the EM fields, is necessary to the design of high powered THz devices. Self-consistent modeling of THz breakdown is challenging as it covers many orders of magnitude in speed (light speed to the neutral thermal speed) and ionization fraction (neutral gas to near full ionization). In prior research, fluid models in the drift-diffusion approximation have found qualitative agreement with experiments for a 110 GHz plasma. In order to achieve better quantitative agreement gas heating, plasma chemistry, and reaction rates that account for steep gradients in density and temperatures will be needed. In this work, an existing three-species (electron-ion-neutral atom) 5-moment model developed by Meier and Shumlak [Physics of Plasmas, 19, 7, (2012)] is extended to include physically motivated non-Maxwellian local electron distributions in reaction rate calculations. Initial results and model validation are presented for THz breakdown in atmospheric argon. |
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TP11.00136: Improving upon Landau and van Kampen-Case: Proper Asymptotics and Disappearance of Decaying Discrete Modes Frank M Lee, Bradley A Shadwick Landau's approach (generalized by Jackson) to the initial value problem for the one-dimensional linear Vlasov--Poisson system shifts and deforms the Bromwich contour around the poles of the analytically-continued dielectric function. For an unstable equilibrium, this produces the growing but not the decaying discrete modes. However, in the van Kampen--Case construction, growing and decaying discrete modes occur together: an apparent contradiction. We present a more general, yet more transparent solution and show that the decaying discrete modes do not ultimately contribute; part of the continuum always exactly cancels the decaying discrete modes. We evaluate the Bromwich integral using properties of Cauchy-type integrals instead of deforming the contour and therefore avoid difficulties arising from the Landau--Jackson analytic continuation. The latter can result in divergences from incorrect asymptotic assumptions, where the initial condition plays an important role in the complex plane that we properly account for. We avoid complicated principal value integrals and singular eigenfunctions of van Kampen--Case; a straightforward Laurent series expansion is used instead. We show specific examples using equilibria and initial conditions with distinct, previously unseen properties. |
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TP11.00137: Closure theory for high-collisionality plasmas with multiple ion species Jeong-Young Ji A general formalism is developed for calculating closures for high-collisionality plasmas with multiple ion species. Parallel and transverse closures can be obtained by solving sets of linearized moment equations for arbitrary mass, temperature, charge, density, and collision time ratios. A convergence study increasing the number of moments shows that practically exact coefficients within 0.4% error can be obtained from 3 moment calculations for parallel closures and from 12 moment calculations for transverse closures. As an example study, closure coefficients for a deuterium-carbon plasma are presented for various temperature ratios across the entire Hall parameter range. |
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TP11.00138: Measuring relaxation times of fluid moments with a GPU-accelerated MD code Jawon Jo, Min Uk Lee, Eric D Held, Jeong-Young Ji The molecular dynamics (MD) simulation is an intuitive and effective tool for analyzing collisional processes of a plasma. It can be used to compute the collision time by measuring the equilibration time of temperatures and momenta and the relaxation time of non-Maxwellian moments. Measuring the higher-order moments requires a large number of particles for small statistical fluctuations. The computation effort for N particles can be reduced from O(N2)to O(NlogN) by computing particle-multipole, instead of particle-particle, interactions. A GPU-accelerated MD code is developed to significantly reduce the wall-clock time of MD simulations. Numerical experiments with the code are performed to measure the equilibration and relaxation times of various fluid moments. |
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TP11.00139: Development of closures based on machine learning for high-collisionality plasmas with multiple ion species Min Uk Lee, Jeong-Young Ji Fluid closures for multi-ion-species plasmas are required to describe plasma phenomena such as edge pedestal transport in tokamaks and multi-component ion flows in the Earth ionosphere. Although quantitative closures can be obtained by solving the general moment equations, analytic formulas of converged closure coefficients become impractical as the number of moments increases. Additional complexities come from combinations of mass, temperature, number density, and charge ratios and the Hall parameter as the number of ion species increases. This work aims to find fitting functions that represent the analytic closure coefficients and can be used conveniently for practical fluid problems. In order to establish the closure functions, we use machine learning for multivariate polynomial regression. Machine learning is based on the training data set constructed by the analytical formulas. The multiple ion parameters constitute the input data set and the analytic closure coefficients constitute the well-labeled output set. The fitted closure functions will be presented for two ion species and an effective-parameter method will be introduced for multiple ion species. |
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TP11.00140: Threshold and simulations of absolutely unstable stimulated Raman backscattering for relativistic phase velocities Jennifer K Gorman, William Arrighi, Jeff W Banks, Richard L Berger, Thomas D Chapman, William A Farmer, Natalie Kostinski, David J Strozzi Recent laser-driven high energy density experiments have generated very high (>10 keV) electron temperatures in under dense plasma conditions that suggest the necessity of relativistic treatment in simulations. Stimulated Raman Scattering, the interaction of light waves with these Langmuir waves, is of great interest, as the relativistic dispersion relation for high phase velocity Langmuir waves has reduced damping compared to the conventional treatment. In continuation from previous work, we conduct physics studies on these Langmuir waves using the relativistic Vlasov equations. Previous simulations confirmed that higher plasma temperatures with relativistic treatment displayed reduced electron potential damping in a collisionless plasma. Given this, it is assumed that relativity will also influence the absolute threshold of uniform plasma parametric instabilities. Moreover, we conduct Raman simulations to demonstrate the amount of backscattering. Using these simulations, we can observe the effect relativity has on backscattering. |
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TP11.00141: Eulerian Finite-Difference Vlasov-Poisson Solver with Non-Uniform Momentum Grid Roland Hesse, Bradley A Shadwick An Eulerian finite-difference method solving the Vlasov–Poisson system is developed with a static, non-uniform momentum grid. The computational cost of this transformation differs negligibly from the uniform case with the same number of grid points. Analytic optimization of curvilinear momentum results from balancing the linear theory field structure against equipartition. A general grid parametrization is tested against classic instabilities and driven cases and is found to provide significant efficiencies over the uniform grid case. This technique introduces implicit distribution of computational resources commensurate to kinetic activity while preserving variationally conserved quantities from the formal bracket. The comparative advantages of this scheme are evidenced by its versatile modularity, adaptability, and extension to relativity. |
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TP11.00142: Calculations of WHAM2 Mirror Neutron Rates and FI Transport using the GENRAY-C/ CQL3D-M and MCGO-M codes Robert W Harvey, Yu. V Petrov, Cary B Forest, J. K Anderson The GENRAY-C ray tracing, and CQL3D zero-orbit-width neutral beam/RF/collisional Fokker-Planck code are applied for calculation of D distribution functions in the WHAM2 mirror configuration, obtaining DD neutron rates, similar to [1]. We compare calculated neutron rates from available 25 keV NB and RF fast wave (FW) power. For 0.5 MW second harmonic FW heating at 26 MHz, we obtain 5e13 neutrons per sec, compared to 2e12 n/s with 1 MW NB power. Electron density is 6e13/cm**-3; Te is 2 keV. The much higher D-energies obtained with FW are very effective for DD neutron production. |
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TP11.00143: Ion kinetic effects and instabilities in the plasma flow in the magnetic nozzle Marilyn Jimenez Jimenez, Andrei Smolyakov, Oleksandr Chapurin, Peter Yushmanov Kinetic effects on plasma flow in a converging-diverging magnetic nozzle due to finite ion temperature and ion trapping are investigated with collisionless quasineutral hybrid simulations with drift-kinetic model for ions and isothermal Boltzmann electrons. It is shown that in the cold ions limit the ion velocity profile agrees well with the analytical theory predicting the formation of the global accelerating potential due to the maximum of the field at the magnetic mirror.The global ion velocity profile is also demonstrated for isotropic and anisotropic distributions of warm ions. Partial ion reflections are observed due to a combined effect of the magnetic mirror and time-dependent fluctuations of the potential due to the wave breaking and instabilities that occur in the regions when the fluid solutions become multi-valued. Despite some reflections, the flow of the passing ions still follows the global accelerating profile defined by the magnetic mirror configuration. In simulations with a partially reflecting source wall, which imitates plasma source and allows the transitions between trapped and passing ions, the global nature of the transonic accelerating solution is revealed as a constrain on the plasma exhaust velocity that ultimately defines plasma density in the source region. |
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TP11.00144: Transport Barrier Properties near the Separatrix of the C-2W Field-Reversed Configuration Lothar Schmitz, C. Lau, H. K Leinweber, T. Roche, H. Gota, R. Smith, T. Tajima In the C-2W Field Reversed Configuration (FRC), a closed-fieldline FRC plasma is embedded in an (open-fieldline) mirror scape-off-layer plasma. Doppler Backscattering measurements show that the statistical properties of density fluctuations change significantly near the excluded flux radius. Radially elongated streamers dominate scrape-off layer transport where E×B flow shear is low (as also confirmed by a positively skewed probability density function (pdf) of density fluctuations, and in global gyrokinetic simulations) [1]. In contrast, strong local E×B flow exhibiting Zonal Flow characteristics, and short radial fluctuation scales dominate inside the excluded flux radius (confirmed by a negatively skewed pdf). Anti-correlation of the rms density fluctuation level and the dominant fluctuating (Zonal) E×B velocity shear is observed in the barrier layer, confirming that Zonal E×B shear limits local turbulence levels. Radial transport barrier formation in both hydrogen and deuterium plasmas maintains a core plasma state characterized by very low ion-scale fluctuation levels [2]. The dependence of turbulence and barrier properties on divertor bias is explored in bias termination experiments. |
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TP11.00145: X-ray imaging of and phase transformation kinetics in shocked Silicon at LCLS Bob Nagler, Hae Ja Lee, Dimitri Khaghani, Eric Cunningham, Thomas Hatcher, Hai-En Tsai, Gilliss Dyer, Arianna Gleason, Silvia Pandolfi, Anne Sakdinawat, Yanwei Liu, Daniel S Hodge, Richard L Sandberg, Eric Galtier We report on first results of a new X-ray imaging diagnostic at the Matter in Extreme Conditions endstation at the Linac Cohorent Light source. |
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TP11.00146: MEC-U: Leveraging LCLS for Precision Plasma Science With a High-Repetition-Rate Petawatt Laser Gilliss Dyer, Eric Galtier, Eric Cunningham, Thomas Spinka, Elizabeth Hill, Frederico Fiuza, Luke Fletcher, Chandra Breanne Curry, Maxence Gauthier, Kai LaFortune, Corey Hardin, Bob Nagler, Hae Ja Lee, Dimitri Khaghani, Siegfried H Glenzer, Jon D Zuegel, Vincent Tang, Selina Z Green, Mikael Martinez, Alan Conder, Alan R Fry We report on a major upgrade to the Matter in Extreme Conditions (MEC) instrument at SLAC's Linac Coherent Light Source (LCLS) providing a world-unique, open-access tool for high-precision studies of dense plasmas and dynamic materials. Through the FES-sponsored MEC-U project a new experimental hall will be constructed to house state-of-the-art high power lasers and target systems. The planned laser systems include a 10 Hz repetition rate 150 J petawatt laser system that can also be run in nanosecond pulse-shaped mode, and a 1 kilojoule nanosecond pulse-shaped laser, with additional space set aside for further upgrades. An efficient and versatile target chamber will support experiments using these lasers together with LCLS X-rays at up to 10 Hz. Hard X-ray FELs are uniquely suited for high-resolution probing of high-power and high repetition rate laser driven experiments, allowing time-resolved, first-principles measurement of fundamental state properties at unprecedented accuracy and precision. A second independent target area will support experiments using the optical lasers independent of the LCLS X-rays, under the auspices of LaserNetUS. We will overview scientific opportunities for laboratory plasma physics, dynamic materials and inertial fusion energy science. |
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