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 JP11: Poster Session IV: In-Person, Hall A (2:00-3:30pm) and Virtual Poster Presentations (3:45-5:00pm)
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Room: Exhibit Hall A and Online |
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JP11.00001: BEAMS: LASER ACCELERATORS Session Chairs: |
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JP11.00002: Ultrafast electron probing of extreme magnetic fields Paul T Campbell, Brandon K Russell, Gennady Fiksel, Jason A Cardarelli, Qian Qian, Karl M Krushelnick, Louise Willingale, Alexander G Thomas Generation of extremely strong magnetic fields (> 0.1 MT) is anticipated during ultra-high intensity laser-solid interactions at next-generation facilities, such as ZEUS laser system at the University of Michigan. Laboratory experiments using these extreme fields can explore the fundamental physics of relativistic, highly magnetized plasmas and create conditions relevant to energetic astrophysical phenomena. However, measuring such magnetic fields poses a significant challenge for commonly used techniques like proton deflectometry as caustic formation and trajectory crossing will prevent accurate retrieval of the field profile. This work investigates the application of GeV-class electron beams from laser-wakefield accelerators for ultrafast probing of extreme magnetic fields. In addition to practical consideration of beam emittance, divergence, and energy spread, the impact of quantum-electrodynamics (QED) effects as the relativistic beam interacts with the strong fields will be presented. |
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JP11.00003: Filter Pack X-ray Spectrum Reconstruction for Betatron Streaking Experiment Rebecca J Fitzgarrald, Yong Ma, Jason A Cardarelli, Paul T Campbell, Mario Balcazar, Andre F Antoine, Nick Beier, Sylvain Fourmaux, Sallee R Klein, Meriame Berboucha, Amina E Hussein, Brendan Kettle, Karl M Krushelnick, Stuart P.D. Mangles, Qian Qian, Gianluca Sarri, Daniel Seipt, Vigneshvar Senthilkumaran, Rob Shalloo, Matthew Streeter, Louise Willingale, Alexander G Thomas For laser wakefield acceleration, single-shot diagnostic techniques are used to obtain the betatron X-ray spectrum. One method is the use of a filter pack in front of an X-ray camera to calculate the critical energy of a synchrotron-like spectrum. The pack is made of strips, each with varying thicknesses of aluminum and copper. To recover the spectrum, the spatial intensity profile is normalized by taking the background from the empty spaces between the strips and interpolating to recover the profile. A critical energy is guessed, and transmission data is calculated. The guess is adjusted to minimize the sum of the squares of the residuals between the real and calculated values, and this final value is taken to be the true critical energy. In betatron streaking experiments, the wakefield follows a curved trajectory as it travels through a transverse density gradient. Emitted X-rays “streak” across the camera, so the spectrum can be retrieved as the emission angle changes, representing the evolution of the critical energy with time. |
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JP11.00004: Geant4 modeling of a filtered scintillator array for the development of a rep-rated beam calorimeter Joanne Low, Kavin Tangtartharakul, Florian Condamine, Stefan Weber, Alexey Arefiev, Mario Manuel Next-generation laser facilities used to study high-energy-density (HED) physics are now moving towards rep-rated operation (~0.1-10Hz). Many of the diagnostics presently in-use rely on single-use media, such as film or image plates (IPs), that require the vacuum to be broken and diagnostic media exchanged before each shot. One of the most prevalent diagnostics used in developing laser-driven radiation sources is a filtered stack of IPs, wherein each IP has a different low-energy threshold for particles of interest (e.g., electrons, photons, or protons). In general, this diagnostic can provide an energy spectrum and energy-resolved beam size information. However, to rep-rate this filtered stack of detectors, the IPs must be exchanged for a media that can be immediately digitized and read out at rep-rates of up to 10Hz; scintillators are one potential option for this application. To this end, a Geant4 model has been developed to study different filter and scintillator configurations to determine sensitivity curves to aid in designing future diagnostics for rep-rated experiments. Results from recent calculations will be presented and discussed. |
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JP11.00005: Detection System for Light Ion Desorption from a Bremsstrahlung Converter Target Alex F Press, Nancy Fujikado, Michael A Jaworski, David C Moir, Martin Schulze, Roger P Shurter, Sebastian Szustkowski The Dual Axis Radiographic Hydrodynamic Test (DARHT) Facility is used to produce X-ray shadow images of hydrodynamic experiments. Both DARHT axes, comprise linear electron accelerators and a target region, where the electron beam strikes a high Z target, producing Bremsstrahlung X-rays. The radiographic image resolution is affected in large part by the electron beam spot size at the Bremsstrahlung converter target. While tuning of the accelerator and the final focusing magnet can produce a small spot size (~1 mm), light ions desorbed from the target material negate a portion of the repulsive electron beam space charge, dynamically over focusing the beam. Measurement of the desorbed ions is highly desirable for both modeling of this process and testing of mitigation methods. Electro-optical sensors can be used to measure the radial electric field produced by the electron beam and light ions, with high resolution of both field magnitude (~5 μV/m) and time (~0.5 ns). With an array of these devices, ion velocity can be inferred, and the system can be used as a time-of-flight mass spectrometer. A prototype of this system consisting of a single measurement is being tested to insure it meets resolution requirements and can operate in high radiation environments. |
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JP11.00006: New developments in the OSIRIS simulation framework Ricardo A Fonseca, E. Paulo Alves, Chiara Badiali, Pablo J Bilbao, Sarah E Chase, Stephen Dilorio, Frederico Fiuza, Thomas Grismayer, Victor Haugaard, Roman Lee, Fei Li, Martin L Lindsey, Bernardo Malaca, Bertrand Martinez, Joshua J May, Kyle G Miller, Mariana Moreira, Zan Nie, Miguel Pardal, Jacob R Pierce, Kevin M. Schoeffler, Rui P Torres, Frank S Tsung, Thales Silva, Jorge Vieira, Marija Vranic, Han Wen, Camilla Willim, Benjamin J Winjum, Xinlu Xu, Yujian Zhao, Viktor K Decyk, Warren B Mori, Luis O Silva The OSIRIS EM-PIC code [1] is a well-established kinetic plasma simulation tool actively used in the numerical modeling of many laboratory and astrophysical scenarios. In this work, we report on the new developments recently introduced into the framework. We address the implementation of new radiation and particle sources, such as ASTRL (Arbitrarily Structured Lasers) pulses, and Ionization injection of spin polarized electrons. We present the new linear Compton scattering algorithm, as well as the overdense algorithm for splitting and damping particles. We also report on the new developments of our QED module, such as the implementation of Bethe-Heitler pair production, and a spin and polarization-related module. Furthermore, we describe new features implemented in the Quasi-3D geometry, for the computation of short-wavelength electromagnetic radiation emitted from particles in this geometry. We also focus on the developments done in the General relativity module, such as static load balancing capabilities and asymmetric filtering adapted to the selected grid spacings and the inclusion of Heuristic pair production models to mimic QED effects. Finally, we present our new implementation of GPU support, including high-order particle interpolation and customized fields solvers. |
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JP11.00007: Summation by Parts Operators for Lagrangian Field Evaluations Adam J Higuet, Bradley A Shadwick In the aim of computing the evolution of electromagnetic potentials for theoretical work, it is common practice to produce wave equations from the analytic Lagrangian and discretize the vector calculus operators post hoc. For most choices of finite difference operators, this results in a set of discretized equations which do not correspond to the discretized version of the Lagrangian. By choosing discrete analogs to derivative and integral operations which preserve integration by parts, so-called Summation by Parts operators [1], the discretized electromagnetic potentials may be derived directly from a discretized Lagrangian and can be rigorously analyzed using the wealth of techniques common to Lagrangian mechanics. We illustrate these considerations with a model of a charged beam traveling through a plasma. |
Author not Attending |
JP11.00008: Efficient modeling laser wakefield acceleration using quasi-3D quasi-static PIC simulations Fei Li, Weiming An, Frank S Tsung, Viktor K Decyk, Warren B Mori High fidelity modeling of laser wakefield acceleration (LWFA) requires 3D large-scale particle-in-cell (PIC) method. 3D PIC algorithms based on the quasi-static approximation (QSA) have been successfully applied to efficiently model the interaction between relativistic charged particle beams and plasma. In a QSA PIC algorithm, the plasma response is calculated based on the QSA form of Maxwell's equations. These fields are then used to advance the charged particle beam or laser forward by a large time step. Since the time step is not limited by the regular CFL condition that constrains a standard PIC code, a QSA PIC code can achieve orders of magnitude speedup in performance. Recently, a new hybrid QSA PIC algorithm that combines another speedup technique known as an azimuthal Fourier decomposition has been proposed and implemented. This hybrid algorithm decomposes the electromagnetic fields, charge and current density into azimuthal harmonics and only the Fourier coefficients need to be updated, which can further reduce the algorithmic complexity. Modeling LWFA in a full 3D PIC algorithm is very computationally expensive due to the enormous disparity of physical scales to be resolved. In the QSA the laser is modeled using the ponderomotive guiding center (PGC) approach. We describe how to implement a PGC algorithm compatible with the QSA PIC algorithms based on the azimuthal mode expansion. This algorithm permits time steps orders of magnitude larger than the cell size and it can be asynchronously parallelized. Benchmarks and comparisons between a fully 3D explicit PIC code (OSIRIS), as well as a few examples related to laser wakefield acceleration, are presented. |
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JP11.00009: Convergence Testing on the EPOCH Particle-in-Cell Code: How many particles are enough? Ricky Oropeza, Ronak Desai, Joseph R Smith, Chris Orban Particle-in-cell (PIC) simulations are a great tool to explore underlying physics in intense laser experiments and to model potential future experiments. However, PIC simulations can be very computationally expensive, taking hundreds of run-time hours even on state of the art supercomputers. Consequently, it is important to understand the most efficient way to perform a particular computation that still yields a sensible result. One important metric for the accuracy of a given PIC simulation is the extent that the particles and fields conserve energy. Numerical heating can occur if the resolution is too low or by using too few macroparticles per cell. In this work we use the EPOCH PIC code to simulate the interaction of an ultra-intense laser with a thin target in the Target Normal Sheath Acceleration regime. We conduct many of these simulations with different numbers of electron and ion particles per cell and analyze the results with correlation matrix techniques to determine suitable parameters for running an energy conserved simulation. |
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JP11.00010: A divergence-free global least-squares approximation method for magnetic field interpolation minglei yang, Diego Del-Castillo-Negrete, Matthew T Beidler, Guannan Zhang Magnetic field interpolation is a major bottleneck in transport computations. To ease this problem, we present an accurate and efficient divergence-free global least-squares (DivFree-GLS) interpolation method for a given set of N_{train} magnetic field point values. The method is mesh-free, the distribution of the training set can be arbitrary, and based on a data-driven reconstruction of the magnetic field using a global expansion of basis functions. The M_{terms} << N_{train} expansion coefficients are obtained by minimizing the cost function of the L2 norm of the difference between the ground truth and the approximate magnetic field and the divergence free condition. An exponential decay of the approximation error as function of M_{terms} is observed and compared with the less favorable algebraic decay of the local spline method with N_{train}. In addition, the DivFree-GLS method exhibits a significant reduction of the computational complexity, compared to local splines, while maintaining a small error in the divergence, even in the presence of magnetic islands and stochasticity. Applications of the DivFree-GLS method to the computation of Poincaré sections using magnetic field data obtained with the M3D-C1 and NIMROD MHD codes are presented and compared with local methods currently in use. |
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JP11.00011: Electron energy distribution formation under recursive accelerations by relativistic laser light Yasuhiko Sentoku, Natsumi Iwata, Misato Hayashi Electron energy distribution is a key for applications of relativistic laser-plasma interaction. We study the electron acceleration in a hot thin plasma created by a relativistic picosecond laser light using a plasma particle-in-cell code, PICLS. The simulation shows that electrons become more energetic than the ponderomotive scaling due to multiple interactions with the laser light. The energy distribution becomes a power-law distribution at quasi-steady state. We model the electron energy distribution formation as diffusion in the momentum space using the Fokker-Planck equation. The properties of the distribution function such as a power exponent are also derived. The energetic electron distribution formation by a kJ-class relativistic laser light results an efficient proton acceleration recently observed in the experiment [1]. |
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JP11.00012: Ion Ring Formation after Laser-driven Ion Acceleration in Thin Film Targets Brady Unzicker, Preston Pozderac, Nicholas Czapla, Douglass W Schumacher High-intensity lasers are able to accelerate electrons to high energies in less than one optical cycle and these hot electrons can efficiently accelerate ion beams to energies exceeding tens of MeV/nucleon. Understanding the characteristics (energy, divergence, etc.) of these beams is key to interpreting experimental results and developing potential applications. In this work, we perform 3D particle-in-cell simulations using the code EPOCH to examine the resulting ion beams that are formed when an intense, short-pulse laser (I ∽ 1021 W/cm2, τ ∼ 30 fs) interacts with a thin liquid crystal target. We show that ion rings with a relatively large opening angle (∼ 5○ – 10○) can form in the angular distribution far from the target. We compare our results to a recent experiment performed at the Scarlet Laser Facility at The Ohio State University and find reasonable agreement. We describe how quasi-static electric fields forming after the laser-plasma interaction lead to ring formation. |
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JP11.00013: Simulation and Measurement of Helicon Wave Fields and Plasma Parameters at the Madison AWAKE Prototype Marcel D Granetzny, Barret Elward, Michael Zepp, Oliver Schmitz The AWAKE project at CERN opens up the frontier of next generation electron colliders using beam-plasma wakefield acceleration. Acceleration gradients exceeding 1 GV/m have been demonstrated using a laser-ionized plasma. However a full scale accelerator will need a reliable, high density plasma source that scales to kilometer lengths with a high degree of axial density uniformity. The Madison AWAKE Prototype (MAP) is utilizing 30 kW of RF power to generate a helicon plasma with expected densities reaching 1020 m-3 in a multi-antenna setup. In order to optimize the density profile, an understanding of wave propagation and power deposition is essential. To this end we have developed a finite element model in Comsol that solves for the quasi 3D wavefields and power deposition for a given temperature, density and neutral distribution. We present comparisons of model predictions to experimental measurements for the power deposition. Further we show the helicon density scaling with magnetic field strength, as measured by a newly developed high-speed heterodyne microwave interferometer system. We also show results from the recently established steady-state high-power operation which was made possible by a new antenna cooling system. |
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JP11.00014: High Time Resolution Axial Particle Balance in AWAKE Helicon Plasmas Michael Zepp, Birger Buttenschön, Barret Elward, Marcel D Granetzny, Oliver Schmitz, Alban Sublet A moderately high plasma density (1021 m-3) with very high axial uniformity is needed to achieve wakefield acceleration of electrons in the GV/m range in AWAKE plasmas. While helicon plasmas are capable of reaching sufficient densities at the beginning of a 5 ms pulse, it is not known if they meet the strict uniformity requirement of 0.25% for use in AWAKE. Using laser induced fluorescence, it is possible to derive a particle balance in helicon plasmas. A new high speed laser induced fluorescence technique is being developed to measure densities and flow velocities with time resolution as short as at least 1 ms. This new diagnostic will be capable of providing density and flow velocity measurements for both argon ions and neutrals, and from this data, the particle balance is derived. This particle balance not only provides the necessary details about the axial density profile, but it also gives insight into the physics of the ion and neutral dynamics that establish this profile. In particular, the plasma pressure gradient that could cause a depletion of neutral particles on axis could have a significant impact on the axial density profile especially in limiting the achievable density in a helicon plasma. |
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JP11.00015: Self-consistent simulations of a PWFA linear collider stage with witness beam realignment using adiabatic ramps Lance Hildebrand, Yujian Zhao, Weiming An, Fei Li, Xinlu Xu, Warren B Mori, Chandrashekhar Joshi Beam driven plasma wakefield acceleration (PWFA) has shown great potential to be the basis for |
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JP11.00016: A scheme for generation and measurement of spin polarized GeV electrons from a PWFA Nainoa M Nambu, Zan Nie, Fei Li, Felipe Morales, Serguei Patchkovskii, Olga Smirnova, Weiming An, Chaojie Zhang, Yipeng Wu, Daniel Matteo, Kenneth A Marsh, Frank S Tsung, Warren B Mori, Chandrashekhar Joshi The generation and acceleration of an electron beam with a high degree of spin polarization is desirable for future plasma-based high-energy colliders. Our recent theoretical and simulations work [1,2] has shown that spin polarized electrons can be produced from photoionization of 4f14 electrons of Yb III ions by a circularly polarized laser, and then accelerated to multi-GeV energies while maintaining their spin polarization in a beam-driven plasma wakefield accelerator (PWFA). An experimental realization of this scheme would require a method of measuring the spin polarization of the accelerated electrons. In our proposed scheme, Møller scattering polarimetry is used to measure the spin polarization of the beam, which involves scattering the beam off of a magnetized target and observing the yield of scattered electrons at specific angles. Measuring the spin polarization of a beam produced from a PWFA presents additional challenges due to the unpolarised drive beam that typically contains nC of charge and a lack of stability from shot to shot. Our spectrometer design addresses these challenges and provides a scheme for both producing and detecting high-energy spin polarized electrons accelerated in a beam-driven plasma-based accelerator. |
Author not Attending |
JP11.00017: Towards a plasma-based acceleration for non-relativistic particles Chiara Badiali, Thales Silva, Bernardo F Malaca, Ricardo A Fonseca, Jorge Vieira The past years have seen a growing interest in plasma-based accelerator technology since it provides a route to more compact, ecological yet powerful accelerators. Nonetheless, even well-established acceleration methods, such as Laser Wake Field Acceleration [1] and Plasma Wake Field Acceleration [2], are only applicable to particles whose velocities are close to the speed of light (relativistic particles). Heavier particles, e.g. muons, are thus excluded from the acceleration mechanism because they are produced with non-relativistic velocities, even though these particles could particularly benefit from plasma acceleration since their finite decay-time represents a challenge for conventional acceleration machines [3]. State-of-the-art techniques to sculpt the spatio-temporal spectrum of electromagnetic wave packets leading to pulses with arbitrary group velocities have been recently developed [4]. |
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JP11.00018: Two-stage acceleration of electrons by intense laser-cluster interaction in strong magnetic environment Kalyani Swain, Sagar Sekhar Mahalik, Mrityunjay Kundu
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JP11.00019: Designing Optical Concentrator Targets for High-Intensity Lasers Matthew A VanDusen-Gross, Kathleen Weichman, David R Harding, Hans Rinderknecht, Alexey Arefiev, Alex Haid A structured target that can act as a plasma mirror to concentrate the final focus of a high-power laser beam, thereby increasing the intensity, would be extremely useful for a variety of applications. In this work we investigate the design of an optical concentrator for improving laser coupling into a micrometer-scale waveguide-like channel. Laser–microchannel interactions have shown potential as a platform for laser-based particle acceleration in computational studies and experiments on the Texas Petawatt and OMEGA EP Laser Systems, but laser-coupling efficiency is limited by pointing stability. Compound parabolic concentrators have been used previously to increase high-power laser intensity on target. However, novel optical concentrator shapes can be optimized for use with realistic focused high-power laser profiles. We present designs of concentrator targets for use in experiments on OMEGA EP and investigate their effectiveness for microchannel experiments. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856 and the Department of Energy under Award Number DE-SC0020431. |
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JP11.00020: High-efficiency and high-quality laser-plasma accelerator stages for a plasma-based linear collider Carlo Benedetti, Davide Terzani, Stepan Bulanov, Carl B Schroeder, Eric H Esarey The viability of next generation plasma-based linear colliders relies on the possibility of accelerating high-charge and low-emittance bunches to high energies over short distances with high efficiency, while keeping a small relative energy spread. Laser-plasma accelerators (LPAs) can operate in different regimes, namely, linear (or mildly nonlinear) stages, where laser guiding is achieved by means of an external wave guide such as a plasma channel, or nonlinear stages where the laser is self-guided through the plasma. For the same laser driver energy, LPAs operating in the linear and nonlinear regime are characterized by different accelerating gradients, stage length, optimal bunch parameters, and acceleration efficiency. In this contribution we present an LPA stage operating in the nonlinear regime providing high-gradient, high-efficiency, and quality-preserving acceleration of electron beams for collider applications. We also discuss some of the beam dynamics challenges associated with laser-driven plasma-based accelerators as applied to multi-TeV-scale linear colliders. |
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JP11.00021: Effects of Radiation Reaction on electron dynamics in Radially Polarized Ultra-Intense Laser Focus Seeded By Field Ionization of High Charge States of Neon Nour El Houda Hissi, Enam Chowdhury The proliferation of multi-petawatt laser experimental systems all around the world is ushering an exciting era of ultra-intense relativistic laser plasma interaction (RLPI) physics. RLPI experiments with complex polarization states are becoming feasible and have motivated interests in radiation reaction (RR) effects. Electron dynamics in a strongly relativistic electromagnetic field are significantly altered by radiation friction force. In this work, we perform a computational investigation of direct acceleration of electrons produced during ionization of underdense neon gas using a tightly focused and radially polarized Petawatt-class short pulse laser by numerically solving the relativistically invariant Lorentz equation incorporating the Landau-Lifshitz form of radiation damping effects. For comparison, we also solve the Lorentz equation without RR force. Semi-classical tunneling ionization and Monte Carlo type sampling of the focal volume are considered in both cases. We observe that the RR force linked with the dissipation of kinetic energy of electrons, which we observed in linear polarization, can also contribute to a significant gain of energy in the case of radial polarization. This phenomenon is directly linked to the radial polarization state of the incident laser beam that results in a strong longitudinal electric field (Ez) when tightly focused, where electrons ionized near the focal center in the presence of RR force experience an important gain of kinetic energy of at least 10% compared to those ionized in absence of RR force. |
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JP11.00022: Higher-order resonance as the main energy gain mechanism during direct laser acceleration of electrons I-Lin Yeh, Louise Willingale, Alexey Arefiev Ultra-high intensity laser-plasma interactions are known to generate forward-directed ultra-relativistic electrons through direct laser acceleration (DLA) of electrons. The electron energy gain is assisted by the quasi-static azimuthal plasma magnetic field driven by the laser. The energy gain is prolonged if the frequency of the transverse oscillations induced by the magnetic field matches the Doppler-shifted laser frequency. A higher-order resonance (e.g. the Doppler-shifted frequency being three times higher than the frequency of transverse oscillations), is also possible, but this regime has remained relatively unexplored. We have examined DLA via higher-order resonances with the help of a test particle model and found that one of these resonances can become the primary energy gain mechanism. The criteria for achieving this regime in terms of laser beam width and plasma density will be presented. |
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JP11.00023: Vacuum acceleration of electrons by a diffracted laser beam Sosuke Kojima, David R Blackman, Michal Elkind, Ishay Pomerantz, Alexey Arefiev To be effective, electron acceleration by a laser beam in vacuum requires efficient electron injection into the beam and a mechanism for counteracting transverse expulsion. These requirements are hard to satisfy with a conventional laser beam. However, recent experiments using the high-contrast 20 TW laser system at Tel-Aviv University have revealed that a conventional laser beam diffracted by a wavelength-scale rod can generate well-directed bunches of energetic electrons. We have performed two-dimensional kinetic simulations and test particle calculations to investigate the impact of the field topology in the diffracted beam on electron acceleration. Our simulations results reproduce the formation of the forward-directed electron bunches seen in the experiment. This suggests that the considered setup has the potential to solve the injection and the expulsion problems. |
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JP11.00024: Third harmonic generation for two-color ionization injection in laser-plasma accelerators Liona Fan-Chiang, Anthony J Gonsalves, Alexander Picksley, Davide Terzani, Carlo Benedetti, Carl B Schroeder, Samuel Barber, Curtis Berger, Cameron R Geddes, Eric H Esarey, Christopher V Pieronek Laser plasma accelerators (LPAs) have promise to be the next generation accelerator for colliders as well as for a number of basic science, industry, security and medical applications. Many applications require high brightness enabled by low emittance. One proposal to achieve ultra-low emittance from an LPA is a two color laser configuration, where a long wavelength laser, with large ponderomotive force, is used to excite a plasma wakefield, while another trailing short wavelength laser is used to ionize inner shell electrons, injecting them in the accelerating phase of the wake [1]. The short wavelength allows for a high electric field for ionization, with low ponderomotive force. Most LPAs use Ti:Sapphire based lasers with central wavelength 0.8 μm. We will present experiments and simulations performed at BELLA Center on generating the third harmonic of short (45 fs), high fluence (30 mJ/cm2), Ti:Sapphire based laser pulses for the purpose of ionization injection in a quasi-linear wake. Features and challenges unique to short pulse, high fluence harmonic generation and characterization as well as how those challenges were addressed will also be presented. |
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JP11.00025: Laser Wakefield Near Critical Density Ernesto Barraza-Valdez, Victor Flores, Toshiki Tajima Laser wakefield acceleration (LWFA) in increased plasma density up to near critical densities shows stronger laser coupling with the bulk plasma. In consequence, the long, coherent, and smooth wake structures found in conventional, underdense LWFA are replaced by multiple modes of low phase velocity wakes. 1-D relativistic Particle-In-Cell code (PIC) simulations were conducted to differentiate between conventional and high-density regimes. The parameters that were varied include the plasma density and laser intensity. We show that these low phase velocity wakes are able to trap a large bunch of electrons from the bulk low temperature, thermal distribution and accelerate them. This analysis has the potential to be extended to experimental results using targets at near critical density or nanomaterials. |
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JP11.00026: Mitigation of the detrimental role of the longitudinal laser electric field during direct laser acceleration of electrons Kavin Tangtartharakul, Ilin Yeh, Hongmei Tang, Tao Wang, Louise Willingale, Alexey Arefiev Next generation laser facilities around the world are rapidly increasing the power capabilities of their lasers. In research studying high-intensity laser-plasma interactions, much of the focus has been to leverage this promising power to significantly enhance the field intensities of the laser at focus. Notably, the peak energy of an electron in vacuum irradiated by a high-intensity plane electro-magnetic wave scales linearly with the laser’s peak intensity. For a tightly focused laser however, the longitudinal components of the laser fields necessarily increase and can prove to be detrimental. By using particle-in-cell (PIC) kinetic simulations, test-particle models, and theoretical results, we show that a less tightly focused laser of the same power can indeed generate noticeably higher energy electrons. In particular, we apply this analysis to a high-intensity laser-plasma setup where plasma electrons have prolonged interactions with the laser through a 1cm long plasma target. In doing so, we highlight the importance of balancing the benefits of high-intensity laser fields with the detriments of the longitudinal components of the laser fields in direct laser acceleration of plasma electrons. |
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JP11.00027: Electromagnetic pulse generation from laser-plasma interactions Kathryn A Wolfinger, Valentina Lee, Gregory R Werner, Michael D Litos, John R Cary Electromagnetic particle-in-cell simulations show that laser-plasma interactions generate a radially propagating and axially polarized electromagnetic pulse, oscillating near the plasma frequency. This EMP and the electrostatic plasma wakefield are replicated with a ponderomotively-driven reduced model which, by eliminating unessential physics, indicates that the EMP can be generated independent of previously reported mechanisms such as external fields, nonuniform densities, and oblique or two-colored lasers. In addition to providing much faster simulations with less computational noise than the PIC simulations, the reduced model also allows for the calculation of the energy lost from the drive laser to the electrostatic wakefield and EMP. The simulations show that the EMP energy varies inversely with the pulse's transverse width, when normalized by the laser energy, while the wakefield energy is largely independent of pulse width. |
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JP11.00028: Controllable Electron Injection Using Co-Propagating Laser Pulses in the Bubble Regime Nicholas Ernst, Yong Ma, Alec G.R. Thomas, Karl M Krushelnick We introduce a novel method of controlled electron injection for Laser Wakefield Acceleration (LWFA) operating in the high-intensity "bubble" regime. In this scheme, a fraction of a high-intensity "driver" pulse is diverted and compressed into a low power, few-cycle "satellite" pulse co-propagating alongside the driver. This satellite is tightly focused off-axis where it acts to perturb bubble formation and drive an asymmetric plasma wave before stabilizing on-axis. Doing so allows for manipulation of the particle separatrix; creating a trigger to overcome the wave-breaking injection threshold and lead to efficient particle trapping and acceleration. 2D and quasi-3D Particle-in-Cell (PIC) simulations support this concept, demonstrating that systematic investigation of the two-beam parameter space (e.g. temporal delay, beam displacement) leads to controllable variance in the electron beam phase space. Results indicate this method could be used to induce self-injection in wakefields at plasma densities and driving laser intensities well below theoretical predictions. The results show promise for an all-optical route to high charge, mono-energetic particle acceleration to GeV energies or enhancement of electron betatron radiation through independent tuning of the satellite pulse.
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JP11.00029: Programmable-Velocity Dephasingless Laser Wakefield Acceleration Manfred Virgil Ambat, John P Palastro, Philip Franke, Hans Rinderknecht, Dustin Froula, Jessica L Shaw In a laser wakefield accelerator, the ponderomotive force of an intense laser pulse propagating through a plasma excites a large amplitude plasma wakefield that can trap and accelerate electrons to relativistic energies. To prevent the electrons from outrunning the accelerating phase of the wakefield, spatiotemporal pulse shaping can be used to propagate the laser intensity at the vacuum speed of light in the plasma over long distances without the need for guiding structures. We present simulations of a novel optical configuration for spatiotemporal pulse shaping that combines a deformable mirror (DM), a spatial light modulator (SLM), and a reflective axiparabola. The DM imparts a radial group delay that controls the time at which each radius reaches its focus. The SLM corrects the unwanted phase-front curvature imparted by the DM while retaining the desired delay. The axiparabola controls the longitudinal location at which each radius focuses. This flying focus improves upon previous designs by offering flexible programmability of the focal velocity with the DM and SLM. This material is based upon work supported by the Department of Energy Office of Fusion Energy under Award Number DE-SC00215057 and by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. |
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JP11.00030: EDUCATION, PUBLIC ENGAGEMENT, AND DEI Session Chairs: |
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JP11.00031: Measurement of the Anomalous Zeeman Effect in Argon Plasma Harrison Adler, Oleg Batishchev In university physics courses, the Zeeman Effect is commonly studied in atomic gases using water-cooled electromagnets and Fabry-Perot etalons. To that end, normal Zeeman splitting in H/D plasmas has been detected [1-2] using long spectrometers in plasma fusion devices operating with strong superconducting magnets. Alternatively, we have developed a method, using a permanent magnet apparatus, to study the Paschen-Back limit in He [3]. This approach was further improved to allow for stronger magnetic fields and combined with a high-resolution spectroscopic system [4]. It was subsequently applied to study anomalous Zeeman splitting in excited neutral gases [5]. In this work, we report our method's extension to the spectrum of ionized argon, allowing students to study the splitting of the ArII emission lines which were originally investigated by Pieter Zeeman and his colleagues [6]. |
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JP11.00032: Light quantum is graviton and light quantum law of universal gravitation Han y yong Quan For the same type of photon, the mass m and wavelength λ are determined, and λ is the distance between two photons. The magnitude of the gravitational force is proportional to the product of the mass and inversely proportional to the square of the distance. For the same photons: m2λ2 must be equal to a constant, and the square root of both sides is obtained: mλ=H——(1), where m is the mass of the photon. The rotation of the macroscopic object makes the radiation centripetal, the radiation of the two objects is centripetal, the vector combination of the gravitational force between the photons is the macroscopic gravitational force between the two objects, and the photon is the graviton. De Broglie wavelength formula: p=mc=h/λ——(2), combine (1) and (2) to get H=h/c——(3). Simultaneous equations (1) and (3) can be solved as follows: m=h/λc, the mass m and wavelength λ of the photon, the gravitational constant is essentially a mass constant, so the gravitational constant can be applied to the microscopic particle—photon, F=Gm2/λ2=Gh2/λ4c2, F=C/λ4, where C= Gh2/c2, the law of universal gravitation of optical quantum mechanics: The magnitude of the gravitational force between two photons of the same kind is inversely proportional to the fourth power of the quantum wavelength. |
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JP11.00033: Increasing STEM interest through the use of the learning environment and instructional technologies. Jorge Carmona Reyes, Judy York, Andrea Parr, Kerri Brady, Augusto Carballido, Truell W Hyde A search for keywords such as workforce development or interest in space physics or plasma physics in major literature search engines provides minimal data on efforts to address the concerns stated in the “Fusion in the Era of Burning Plasma Studies: Workforce Planning for 2004 to 2014” related to attracting students into fusion science and/or engineering careers. The CASPER group has produced a series of interventions to address this issue that includes CASPER’s seamless pathway and the CASPER physics circus. More recently, CASPER members have partnered with a professional development institution and an architectural firm to measure and produce interventions at the elementary school level that are designed to increase learning skills such as critical thinking, collaboration, self-reflection, and student engagement. This ongoing, longitudinal study started prior to the Covid pandemic and as such is now providing data to compare effects of the pandemic, recovery-from-the-pandemic efforts, efficacy and impact on student engagement, and correlation to STEM areas. These traits have been identified as the critical elements required to build confidence and interest in STEM and consequently in areas of Physics. Thus, any proper understanding or measuring of these STEM traits will provide significant information into designing proper interventions to increase and enhance STEM interest at the secondary school level. This presentation will discuss current efforts by CASPER and its collaborators to increase the learning skills mentioned above and student engagement. It will also discuss how this is measured using an innovative statistical analysis (Rasch analysis) that produces a linear scale that can be used to compare results across different groups. |
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JP11.00034: Who is This Energy For?: An Ethnography of Fusion Energy and Inclusion Alice Chen Fusion energy has been hailed as the “silver bullet” for climate change and non-carbon based energy production. It is clear that a global energy transition must happen within the next few decades, and fusion is one resource that could potentially accelerate that transition. Fusion’s increasing prominence amongst financial investors as well as the United States government has made more apparent the lack of diversity and inclusion not only within plasma physics, but energy production and distribution more largely. Will a clean energy transition necessitate a move away from capitalism’s extractive practices or is clean energy doomed to repeat the same violent mistakes of carbon production? As an anthropologist who has spent over a year studying the fusion community, DEI is an increasingly talked about, but a still relatively marginalized practice within institutions. This presentation explores what is necessary to increase diversity within the physics community, what must be considered in creating a more inclusive energy source, and how discourse around fusion and fusion financing influences our own abilities to imagine cleaner and more just futures. |
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JP11.00035: PPPL's Apprenticeship Program - Training the Next Generation of Technicians Andrew P Zwicker, Diana Adel, Kristen Fischer, Shannon Greco, Andy Carpe, Al von Halle PPPL's growth and success depends on our ability to develop, recruit, and retain a diverse staff who reflect our community and the nation. PPPL currently runs a variety of workforce development programs to educate the next generation of scientists and engineers however, until recently, we had not focused on our technical workforce which is also aging rapidly and essential for the successful delivery of our scientific missions. In response, PPPL started a USDOL registered apprenticeship program in 2019 focused on attracting a diverse pool of technicians into fusion energy and plasma sciences. Apprenticeships have been a reliable pathway for training workers for good jobs and allowing them to earn while they learn. Recently, there has been a renewed focus on apprenticeships at both the federal and state level. The skills needed to build complex machines (e.g. tokamak) are different from a typical apprenticeship program, but apply to many high-tech industries. Over 4 years, our participants spend 8000 hours training in their speciality and 576 hours in the classroom. We currently have apprenticeships in mechanical and electrical technician, electronics, welding, machinist, IT generalist/cybersecurity, and HVAC. |
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JP11.00036: Young Women's Conference in STEM across the US Deedee Ortiz, Julie Manns, Elizabeth Starling, Arturo Dominguez, Shannon Greco
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JP11.00037: USFusionEnergy.org: A community website for US Fusion public engagement Arturo Dominguez, Steffi J Diem As the US Fusion community transitions towards a path of fusion commercialization, it is important that it engages with the US public, both, to help attract the future scientific and technological workforce, as well as to build support for the fusion efforts. |
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JP11.00038: HIGH SCHOOL RESEARCH Session Chairs: |
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JP11.00039: Design Improvements in Dielectric Barrier Discharge Plasma Torches for Medical Applications Krishnaveni Parvataneni, Sohail H Zaidi Low-temperature dielectric barrier discharge (DBD) plasmas are used for rapid wound healing and sterilization. Plasma temperatures and radicals (reactive nitrogen/oxygen) play a vital role in the healing process. In preliminary designs, plasma was generated in a dielectric tube where plasma characteristics could not be changed without changing the input power or gas flow rates. In a new design a variable outer electrode was used to control the plasma jet characteristics. Another manifestation of this design appeared as a multi-electrode plasma torch where multiple fixed outer electrodes were used. The traditional DBD torches produce plasma jets and are not suitable for bacteria mitigation on larger surfaces. For this purpose, a DBD plasma sheet generator was designed. In this presentation, we analyze the design of multiple plasma troches and measure the gas temperatures and plasma vibrational, rotational, and excitation temperatures. Helium was used as the working gas in all experiments and 20-30 kV/30-50 kHz AC voltage was applied. An Ocean Optics UV-VIS spectrometer was used to conduct spectroscopy and SPECAIR was employed to estimate plasma temperatures. Detailed analysis of the experimental results will be included in this presentation. |
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JP11.00040: Development of multiple Langmuir probe designs and user-friendly probe analysis techniques for low temperature plasmas at the Magnetized Plasma Research Labs (MPRL). Matthew J Patkowski, Jared C Powell, Saikat Chakraborty Thakur, Edward Thomas Langmuir probes are used as standard plasma diagnostic techniques in most low temperature plasma laboratories. However, depending on the specific experiment, modifications are necessary for achieving a particular goal. For example, in the RF powered linear plasma device Auburn Linear EXperiment for Instability Studies (ALEXIS), lack of RF-compensation of the Langmuir probes might lead to an artificially high electron temperature measurement. We plan to upgrade ALEXIS from a low power inductively coupled device to a higher power (~ 1 kW) helicon plasma device and hence we are constructing a new RF-compensated Langmuir probe necessary at the higher plasma densities. We also built a hook probe for the Magnetized Dusty Plasma eXperiment (MDPX) to study the perturbation due to a larger probe or a dust shaker. Finally, we are developing analysis codes using open-source programming, Python, for user-friendly Langmuir probe analysis techniques to measure the electron energy distribution functions and to test different theoretical models of Langmuir probe analysis. |
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JP11.00041: Examining Alternative Numerical Algorithms for the Accurate and Robust Study of Turbulence Shiv Seshan, Jason Tenbarge, James Juno Although it lacks a precise quantitative definition, turbulence is a phenomenon which occurs in many dynamic fluids. A turbulent fluid is characterized by fluctuations across a range of length scales, with energy cascading down from larger to smaller length scales before being dissipated as heat at the smallest length scale. Since turbulence involves spatial and temporal quantities which span many orders of magnitude, it is difficult to model through discretizing the differential equations which govern fluid mechanics. Indeed, conventional discretization schemes such as the wave-propagation method often fail to accurately capture the behavior of turbulent plasmas. As a comparably computationally expensive alternative to the wave-propagation method, we consider the Kinetic-Energy Preserving (KEP) Scheme. To compare the KEP and wave-propagation methods, we examined two-dimensional turbulent systems like the Orszag-Tang vortex. By implementing the KEP scheme for the five moment, two-fluid equations, we obtained a richer, more accurate portrait of turbulent behavior in plasmas. |
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JP11.00042: UNDERGRADUATE RESEARCH Session Chairs: |
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JP11.00043: Dynamics of Hydrogen Species in the Presence of a He Bubble within SiC Michael D Ashburn, Zachary J Bergstrom, Jerome Guterl, Stefan A Bringuier Molecular dynamic simulations are performed with LAMMPS to assess the effect of He bubbles on H diffusion energetics and the mechanical properties of SiC. Silicon carbide (SiC) is currently being studied as a plasma facing material in tokamak fusion devices due to its excellent thermo-mechanical/chemical properties, irradiation tolerance, and low-activation. During the fusion process, helium and hydrogen atoms are implanted into the near-surface region of plasma-facing components. The helium atoms form bubbles that degrade the mechanical properties of the material, and affect transport and retention of hydrogen. The hypothesis is the hydrogen atoms will migrate towards the helium bubbles and induce structural degradation. This information can then be used to better understand the synergistic effects between He bubbles and H in SiC. The results can then be compared to that of similar simulations done on tungsten to illustrate if SiC is as applicable as the current leading plasma facing material. |
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JP11.00044: Characterizing EC Transmission Line Losses and Reflections at DIII-D Zachary Bayler, Michael P Ross, Antonio C Torrezan, Esteban Bagdy, Clayton Gray, John Lohr, William Grosnickle, Yuri A Gorelov, Jared P Squire, Mirela Cengher Electron cyclotron current drive is used in fusion devices to drive off-axis current to control instabilities and to improve confinement. Its efficiency plays into the overall efficiency when considering future fusion power plants. There are several significant loss mechanisms in the transport of the microwaves from the gyrotron to the target, including ohmic loss in the waveguide and miter bends, and reflection from the miter bends. Currently estimated losses are 1.5% per miter bend at DIII-D, which compounds significantly along paths that can have as many as 15 bends. At present, there is a disparity between the expected and measured power values at the dummy load. Through additional calorimetric measurements and waveguide temperature measurements, we will better quantify the losses and improve the estimate of the EC power launched into the tokamak. Additionally, gaining a better picture of reflection could provide an important tool to help avoid damage to the gyrotrons. The resulting improved understanding of energy transport from gyrotrons to the tokamak will facilitate optimization of future EC systems. |
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JP11.00045: Comparison of EPED-NN Predictions to the Large DIII-D Experimental Pedestal Database Anson Braun, Florian M. Laggner, Brian Sammuli, Colin Chrystal, Shaun R Haskey, Sterling P Smith, Philip B Snyder, Emi Zeger We compare pedestal structure predictions of the EPED model to experimental data from DIII-D H-mode discharges. EPED-NN (neural net) and TokSearch tools are used to accelerate the process of EPED runs and experimental data processing, which enables novel comparisons across thousands of discharges. We establish a shape-independent edge localized mode (ELM) detection method for determining the pre-ELM EPED-NN input parameters and gathering pedestal profile measurements from Thomson scattering and charge exchange recombination spectroscopy (CER). We find EPED-NN predictions serve as a reasonable upper-bound for pedestal height and the simple scaling for pedestal width based on the normalized poloidal pressure at the top of the pedestal agrees well with experimental data. For the pedestal height, we find similar dependencies in plasma triangularity and pedestal electron density between measured and predicted results. |
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JP11.00046: ELM Filtering Algorithm Using Only Langmuir Probe Signals Joseph S Buck, Dinh D Truong, David Eldon A novel edge localized mode (ELM) filtering algorithm for fixed Langmuir probes (LP) data has |
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JP11.00047: Influence of Plasma and Machine Parameters on Time to First ELM in DIII-D Daniel A Burgess, Andrew O Nelson, Carlos A Paz-Soldan Feature selection via multilinear regression is performed on 506 H-mode discharges on DIII-D, highlighting the parameters most influential on the timing of the first edge-localized-mode (ELM) event after an L-H transition. This database study illuminates key parameters that can be used to delay the advent of ELMs after entering H-mode, extending the window for establishing ELM-suppression via resonant magnetic perturbations (RMPs) to avoid damaging plasma-facing components in ITER or future fusion reactors. Database time-to-first-ELM in DIII-D ranged from <10 ms to 1200 ms, and all discharges using RMP or no-ELM regimes were excluded. Results show linear correlations between poloidal beta and ohmic power sampled at the L-H transition and the time-to-first-ELM, especially in discharge subgroups with similar triangularity. Increased plasma pressure at the L-H transition and the strength of the plasma shape appear to influence the time-to-first-ELM. This investigation will be further generalized with additional machines in an effort to avoid systematic errors and provide suggestions for optimizing RMP application before the first ELM in future devices. |
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JP11.00048: Lower hybrid drift waves during reconnection in Earth's magnetosphere Izzy Thomas, Hantao Ji, Rahul Banka, Narges Ahmadi, Jongsoo Yoo, Li-jen Chen Magnetic reconnection, the breaking and reconnecting of non-parallel magnetic field lines at the intersection of inflowing plasmas, is a source of abundant free energy that heats particles throughout the universe. Observations by the Magnetosphereic Multiscale (MMS) mission reveal the lower-hybrid drift waves (LHDWs) during many of magnetic reconnection events in Earth’s magnetosphere. This study examines the LHDWs during multiple events to understand the role of these waves in magnetic reconnection during which magnetic energy is transferred to kinetic energy of electrons. Initial results of this work demonstrate that βe is related to the type of LHDW observed, and the wave power and the change in electron temperature are positively correlated. |
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JP11.00049: Development of a capacitively coupled and inductively coupled dual plasma source. Alexander D Davies, Saikat Chakraborty Thakur, Edward Thomas Dusty plasma is a four-component plasma consisting of electrons, ions, neutral gas, and microparticles (dust) which collect charge from the surrounding plasma environment. In situ diagnosis of a dusty plasma system with conventional probes is very challenging as the inserted probes can perturb the dust and produce voids. Hence a long-term goal is to use laser-based plasma diagnostics that can be used even in the presence of dust. Here we show the design and characterization of a dusty plasma chamber which has both capacitively and inductively coupled dual plasma sources compatible with parallel plate DC discharges and RF power. This will be used as a target plasma chamber, capable of producing a large range of plasma densities (10^9 – 10^11 cm^-3), along with our tunable, pulsed dye laser, to test laser-based plasma diagnostics techniques such as Laser Induced Fluorescence (LIF) and Cavity Enhanced Absorption Spectroscopy (CEAS). |
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JP11.00050: Aligning the Thompson Scattering and Charge Exchange Recombination Diagnostics Using Neutral Beam Emission at DIII-D Abigail Feyrer, Shaun R Haskey, Colin Chrystal This work addresses discrepancies in the alignment of the H-mode pedestal profiles of the electron and ion properties as measured by the Thompson Scattering and the Charge Exchange Recombination Spectroscopy (CER) diagnostics on DIII-D plasmas. While alignment of these profiles is key for accurate studies of pedestal physics, misalignments can occur due to differences in the poloidal and toroidal locations of the measurements and departures from axisymmetric magnetic fields. Emission from neutral beam particles due to impact excitations is measured by the Main Ion CER (MICER) diagnostic and is used to infer electron density at the same locations as CER measurements. This measurement is compared with the electron density measured by Thompson Scattering which then enables alignment of ion and electron profiles. FIDASIM simulations are used to infer electron densities and assess various effects on the beam emission such as neutral velocities and the finite excited state lifetime. This analysis is performed on historic DIII-D shots as well as shots from the 2022 experimental campaign. |
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JP11.00051: High Power Impulse Magnetron Sputtering Based Ablator Development for Laser Fusion Applications Steven L Frankowski, Hongwei Xu, Priya Raman, Fred Elsner, Haibo Huang There is an increasing demand for thin- and thick-walled, gas impermeable metal capsules for High Energy Density applications. Gas impermeable capsules are presently fabricated using Direct Current Magnetron Sputtering (DCMS) with low success rate. Previous research indicates gas impermeability has a strong positive correlation with film density because higher thin film densities increase the likelihood of coatings being gas impermeable. DCMS coatings are not dense enough to meet the gas permeability requirement. High Power Impulse Magnetron Sputtering (HiPIMS) is a promising magnetron sputtering technique that is capable of depositing highly dense coatings with stronger adhesion to the substrate compared to DCMS. This work investigates the use of HiPIMS to deposit gas impermeable ablator coatings for laser fusion applications. Metrology results including gas permeability tests like Kr leak tests on metal coatings deposited using HiPIMS are presented. Additionally, DCMS-HiPIMS hybrid techniques to improve the gas permeability are also explored. |
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JP11.00052: Design and assembly of the LTX-ꞵ Soft X-ray and Lyman-?? Toroidal Diagnostic Sophie M Redd, Anurag Maan, Javier Morales, Santanu Banerjee, Richard Majeski, Kevin L Tritz The Lithium Tokamak Experiment (LTX) - ꞵ is a low aspect ratio spherical tokamak used to test lithium as a plasma facing material. A toroidal soft x-ray/Lyman-?? diagnostic has been commissioned for LTX-ꞵ. The diagnostic was originally designed and built by Johns Hopkins University for use on NSTX-U and is being adapted for use on LTX-ꞵ to help diagnose MHD modes and neutral density profiles for low recycling discharges in LTX-ꞵ. It is composed of five arrays of 20 photodiodes each, consisting of two arrays aimed at the high field side, two arrays aimed at the low field side, and one array aimed at the whole radial span. The array pre-amplifiers were calibrated using a simple LED and diode array setup. Line integrated emission from each diode will be inverted to construct a radial profile. The diagnostic sub-assembly is installed on a tangential port at the midplane of the torus. Two 5 µm beryllium filters are used with two photodiode arrays, one for the high field side and one for the low field side, to retrieve soft x-ray ranges (100eV to 400eV). The toroidal Lyman-?? array is also composed of two diode arrays each with its own narrowband Lyman-?? filters. The design and assembly of the diagnostic are presented in addition to initial data. |
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JP11.00053: Optimized Optical Imaging Setup for Nonneutral Plasma Diagnostics Larry Zhao, Joel Fajans, Josh Clover Images of nonneutral plasmas are commonly obtained by releasing the plasma onto an MCP/Phosphor and observing the image with a camera. The temperature of the plasmas can be obtained from the time history of the plasma particle hitting the MCP as measured by a SiPM detector. Both of these applications work best with bright (both overall brightness and individual pixel brightness), large, clear images. These properties can be enhanced with an intermediate relay lens, but standard glass lenses of an appropriate diameter (10cm) are expensive and have significant spherical aberrations as they are not in the thin lens regime. Here we report prototyping studies with a Fresnel lens and report on the magnification, image clarity, and brightness. The results from this study will be applied to plasmas at the ALPHA antimatter experiment at CERN. |
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JP11.00054: Plasma Vertical Velocity Measurement from Unintegrated Magnetic Signals Michael Jones, Wilkie Choi Due to the vertical instability of an elongated plasma, it is necessary to provide an active feedback system to control the plasma's vertical position. Modern magnetic diagnostics, which require integration to calculate the magnetic field, are insufficient for future devices with long run-times due to the integration drift introducing a non-negligible error. This work explores the possibility of using the unintegrated signals from Mirnov coils to directly calculate the vertical velocity of the plasma, which can be used in a feedback control system that partially suppresses the growth of the vertical instability. A code has been developed to perform this calculation in real-time. The effects of vessel wall eddy currents are taken into account in the calculation. By delegating the fast response portion of the vertical stability control problem to unintegrated magnetic signals, the plasma position can be controlled on a longer timescale using slower diagnostics, such as a camera, that can circumvent the integration drift issue. |
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JP11.00055: Quantitative interpretation of mass spectra from DIII-D plasma-facing materials and characterization of their gas retention properties Tierney Kim, Igor Bykov, Gregory Sinclair Sustainable operation of a future fusion device relies on low tritium retention in the wall. A standalone thermal desorption station has been used to quantify deuterium retention in graphite tiles used as plasma-facing material in the DIII-D tokamak. Thermal desorption of samples from the divertor of DIII-D was evaluated as a method for fusion fuel recovery. The amount of released fuel was evaluated using calibrated thermo-desorption spectroscopy of deuterium. Samples that underwent short-term heating desorbed 4x1021 atoms/m2 of deuterium after reaching 550 oC. Continued use of calibrated mass-spectroscopy is proposed for the measurement of deuterium evolved during cryo pump regeneration and glow discharge cleaning (GDC). Dual mass-spectroscopy (m=4, 6) can discriminate deuterium and He during He GDC and would provide more insight on how to distinguish deuterium in alternative settings. |
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JP11.00056: Building a Radio Frequency Plasma Source for DIII-D Neutral Beam Applications Daniel A Klasing, Brendan J Crowley, J T Scoville, Joel Hurtado The Miniature Arc Chamber Experiment (MACE) is a tabletop scale device used to emulate the filament driven arc chamber of the ion source of the Neutral Beams system at DIII-D. It was developed to study arcing and component failures of the ion source under normal conditions and particularly for helium operations. Now with a view to enhancing the capabilities of DIII-D, attention has turned to increasing neutral beam power. To achieve greater NBI power a higher density plasma source needs to be developed. To this end, The MACE device has been converted to an RF inductively coupled plasma (ICP) source. Here we present an account of the project to convert the MACE device. The control software was modified using python so that it could interface to the required components. A matching network was built using variable capacitors to match the 50 ohm impedance output of the amplifier. Argon plasma was created and verified through spectroscopy and Langmuir probe data. The purpose of the device is to gain knowledge of RF ICP operation and inform the design of a new ion source for DIII-D. |
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JP11.00057: Synthesis and Characterization of W/SiC Compositionally Graded Film as a Potential Plasma-facing Material Zihan Lin, Carlos Monton, Stefan A Bringuier Tungsten (W) is a promising plasma-facing material due to its low physical and chemical sputtering yield but suffers from embrittlement and blistering. A potential alternative is silicon carbide (SiC) due to its low neutron activation and favorable thermomechanical properties but is more prone to sputtering. In this work we explore synthesis and benefits of W/SiC compositionally graded films given W and SiC have a good mechanical and chemical compatibility owing to their similar coefficients of thermal expansion and stable binary compounds. Preliminary W/SiC coatings have previously been synthesized and exposed using the DiMES apparatus in DIII-D. The present study improves upon the coating deposition process for synthesis of W/SiC films. Microstructural images are obtained via SEM and chemical composition is qualitatively assessed by electron energy dispersive x-ray spectroscopy line scans across the film. Finally, density functional theory calculations are performed to assist in predicting the stability of various structures/phases in the composition regimes of synthesized W/SiC samples. |
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JP11.00058: Design and development of a versatile acousto-optic based filterscope for fusion plasma diagnosis Jacob G Schellpfeffer, Alessandro Bortolon A new filterscope concept is proposed leveraging an acousto-optic tunable filter (AOTF) in-lieu of conventional interference filters. The AOTF operates through Bragg diffraction of RF-driven acoustic wave allowing the central wavelength passing through the filter to be varied in microseconds. The adoption of an AOTF allows fast wavelength hopping to study of different emission lines from a single sightline within the same plasma discharge. A prototype is designed and developed based on an AOTF operating in the visible spectrum from 400–650 nm, with wavelength resolution of 1–2 nm across the range. Two optical outputs allow simultaneous measurement of the filtered light through a photodiode and the rejected spectrum with a dedicated spectrometer. A python-based codebase has been developed to program the AOTF operation by specifying the desired complex time series of wavelength interrogation, as well as to control the oscilloscope/digitizer to store the measured signal. Gas light sources are used to characterize the AOTF’s spectral response to acoustic frequencies before proof of concept tests on DIII-D. |
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JP11.00059: Precise reconstruction of plasma equilibrium using Alfvén eigenmode spectroscopy Carlos J Sierra, Xiaodi Du, Michael Van Zeeland, Deyong Liu, William Heidbrink Precise reconstruction of plasma equilibria is essential to the successful operation of a nuclear fusion device; however, the accuracy of the reconstructions is often compromised by large uncertainties in safety factor (q) profiles in the plasma core. On the other hand, reverse-shear Alfvén eigenmodes (RSAE) are often destabilized in advanced plasma scenarios with reversed magnetic shear, and their presence contains important information about plasma equilibrium, this is known as ‘AE spectroscopy’. The radial mode structure of RSAEs peaks near qmin, the minimum q, and mode frequency is sensitive to the evolution of qmin [1]. To routinely extract qmin information from RSAE activity, a model is developed for the best-fitting of experimentally-measured RSAE frequencies to theoretically-predicted ones with minimum human interference. The accuracy of EFIT reconstructions [2] is largely improved by inclusion of RSAE-derived constraints on the radial location and the temporal evolution of qmin . |
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JP11.00060: Efficient modelling of plasma dynamics using Julia Benjamin T Taczak, Federico D Halpern, Jerome Guterl, Tess Bernard Nonlinear modelling of plasma dynamics in massively parallel computers is an essential aspect of fusion energy research. Most high performance computing plasma simulations utilize programming languages, such as C or Fortran, that sacrifice user friendliness and flexibility for efficiency. The goal of this project is to demonstrate the viability of Julia as an option for developing efficient, GPU enabled high-performance computing plasma simulation codes. Julia enables flexible and user-friendly workflows for easier development and extension. Scripting tools are used to generate the numerical representation of the plasma fluid equations for a variety of plasma modelling problems. A nonlinear MHD model is implemented to carry out extensive performance and physics benchmarks to validate the new approach. |
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JP11.00061: "Gas Cell" for X-Ray Opacity Measurements Stephen Wang, Ruben Santana, Haibo Huang, Kevin Sequoia X-ray opacities of low Z elements control the rate and the path of stellar evolution. High Energy Density (HED) experiments are being conducted at major facilities such as Sandia’s Z machine and LLNL’s National Ignition Facility (NIF) to quantitatively understand the increased “hot” opacity under HED conditions, as compared to “cold” opacity values in ambient environments. The accuracy of target areal densities used in HED experiments are limited by the published x-ray opacity databases which are used in data conversion. The databases can be improved by direct opacity measurements with modern equipment. We pioneer an “AutoEdge” x-ray absorption measurement system for x-ray database revisions on metal elements. In this work, we build an additional “gas cell” to allow for such measurements on gaseous elements. We will start with argon, to establish capabilities, and in the future, extend to oxygen which is particularly relevant to solar opacity. |
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JP11.00062: Evaluation of spatiotemporal dynamics of pedestal density fluctuations during inter-ELM cycles on DIII-D Jamie L Xia, Zheng Yan, George R McKee, Richard J Groebner, Terry L Rhodes, Shaun R Haskey, Jie Chen, Florian M. Laggner We investigate the spatiotemporal dynamics of density fluctuations during the cycles between Edge localized modes (ELMs) and the mechanisms that limit the gradient using the beam-emission spectroscopy (BES) at DIII-D. ELMs are triggered in the H-mode pedestal when the pressure increases to the Peeling-ballooning (PB) instability boundary, leading to an expulsion of particles and heat across the closed flux surfaces. It is predicted that different turbulent modes in the pedestal have various dependencies on parameters such as q95 and profile gradients. Turbulence characteristics are measured between ELMs at different q95 and temperature gradients through varying plasma current and input power (NBI & ECH). Initial time-averaged analysis has shown dramatic changes in density fluctuations characteristics with stronger electron diamagnetic direction propagating modes at higher ECH power and q95. Detailed dynamics of turbulence characteristics in between ELMs are being analyzed. This analysis will provide rich ‘fingerprints’ data to compare with the existing theories and simulations. |
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JP11.00063: Validating the linear model in TGLF with linear CGYRO simulations using experimental DIII-D cases Joseph B Hall, Tom F Neiser, Orso M Meneghini, Sterling P Smith, Gary M Staebler, Emily A Belli, Jeff Candy In order to study present fusion experiments, and plan future fusion reactors, it is important to accurately model the heat and particle losses due to turbulence in magnetically confined plasmas. The trapped gyro-Landau fluid code (TGLF) is a quasi-linear model of gyrokinetic turbulence that relies on high-fidelity simulations with the CGYRO code for calibration. To validate the accuracy of the linear model in TGLF, the CGYRO code is run in its linearized setting for a range of experimental cases from the DIII-D tokamak. In general, the linear growth rates and quasi-linear weights of TGLF and CGYRO agree well, with better agreement found at the ion scales than the electron scales. There are also cases where an overprediction in the linear growth rates of kinetic ballooning modes by TGLF causes an overprediction of heat flux. By focusing on cases with deviations between TGLF and experiment, these linear CGYRO simulations identify any contribution to this deviation from the linear model in TGLF. These results from ongoing work will help validate the linear component of the TGLF model and will inform future model development and calibration efforts. |
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JP11.00064: Prototyping of a tunable filterscope based on acousto-optic filters for tokamak plasma spectroscopy Saad Ayub, Jacob Schellpfeffer, Alessandro Bortolon We present the spectral characterization of a prototype filterscope leveraging an acousto-optic tunable filter (AOTF) operating in the wavelength range 400-650 nm. Using vibrational modes to selectively deflect a wavelength of light, AOTFs provide fast arbitrary wavelength interrogation without moving parts. The instrumental function of the system is determined through wavelength sweeps across line emission from Ne, Hg, and Xe using commercial spectral lamps, finding a FWHW~1-2 nm across the wavelength range. Full range sweeps are then used to perform a wavelength calibration as a function of the vibration frequency applied to the AOTF. A lambertian absolutely calibrated source is used for photometric calibration and to determine the diffraction efficiency. The commissioned prototype can be deployed on the DIII-D tokamak to demonstrate dynamic measurements of deuterium and impurity line emissions from the plasma edge. |
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JP11.00065: Design, Construction and Assembly of Vacuum Boron Dropper Scale Courage Lahban, Alexander Nagy As a method of plasma control, boron is inserted into magnetic fusion devices to enable real-time wall conditioning of plasma-facing components and prevent wall outgassing. We present a design to modify a boron Impurity Powder Dropper piezo feeder, such that the feeder is upgraded to include a vacuum-resistant precision weight scale to quantify the mass of boron injected into the plasma. The modification uses a method of electromagnetic force restoration applied to measure the dropper weight change and obtain the active mass and flow rate of materials within a pulse. Present material measurement techniques use light subtraction through a falling powder stream which requires calibration for a specific type of powder and is not accurate enough for quantitative measurements. This uncertainty is substantially reduced with an incremental mass measurement, eliminating the inaccuracies of light subtraction |
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JP11.00066: Asymmetric Mirror Confinement Isaac AshLind, Nathaniel Fisch, Ian E Ochs, Elijah J Kolmes, Tal Rubin, Mikhail Mlodik Mirror machines are generally symmetric both azimuthally and axially. However, an axial asymmetry can be introduced either through asymmetric mirror ratios at the opposite ends or in the shape of the strength of the axial magnetic field even at the same mirror ratio. In either case, there is the opportunity for selective detrapping at one end or the other. A potential application of asymmetrical mirror particle transport is the generation of a toroidal current in a bumpy torus. |
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JP11.00067: Characterization of Lower Hybrid Drift Waves During Reconnections in Earth's Magnetotail and its Relation to Electron Heating Rahul Banka, Izzy Thomas, Hantao Ji, Erik Ji, Maitian Sha, Narges Ahmadi, Jongsoo Yoo, Li-jen Chen Magnetic reconnection is the process where the topology of magnetic field lines is reconfigured, and various plasma species are energized. Reconnection events are observed by the Magnetospheric Multiscale (MMS) mission, which consists of four identical satellites orbiting the Earth's magnetosphere. By measuring various fundamental quantities in both electromagnetic fields and plasma particles, the MMS allows the detailed analysis of reconnection processes, one of which is Lower Hybrid Drift Waves (LHDW). This study focuses on LHDW in twelve magnetic reconnection events in the Earth's magnetotail to characterize how LHDW properties differ in the magnetotail and in the magnetopause. The magnetotail and magnetopause have different plasma parameters with different magnetic reconnection geometry. The magnetotail has a low plasma density, high temperatures, and smaller guide fields compared to reconnection fields. Magnetic reconnection in the magnetotail tends to be more symmetric, whereas more asymmetric in the magnetopause. Due to these differences, LHDWs exhibit different characteristics which require different data analysis techniques. Furthermore, the relation of LHDWs to electron heating is also investigated. |
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JP11.00068: Machine Learing-Boosted Diagnostics Using Autoencoders Noah A Borthwick, Noah R Mandell, Ammar Hakim, Ralph Kube While plasma simulations provide a complete picture of the plasma state, the same cannot be said about measurements. To better perfect our diagnostic tools, synthetic diagnostic data can be calculated using the expected response of various sensors using the simulation data. But in order to find a simulation that reproduces the measurements, computationally expensive trials may be required. |
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JP11.00069: Investigating Guiding-Center Versus Full Orbit Effects with ORBIT-GPU Nathaniel Chen, Phillip J Bonofiglo, Garrett Wright, Mario L Podesta ORBIT is a particle-pushing code that uses Hamiltonian mechanics to calculate the Lorentz force on particles in magnetic confinement devices. ORBIT acts on particle guiding centers and ignores gyromotion. Given magnetic equilibria and perturbations, ORBIT can analyze particle transport, characterize wave resonant interactions, and produce Poincaré maps, all of which are useful for investigating energetic ions. Recent leaps in graphical processing unit (GPU)-enabled parallel processing such as compute unified device architecture have motivated ORBIT's adoption into a GPU-optimized format. One important performance factor is the speed of simulating many particles when analyzing distributional effects. Since the magnetic field strength drops off inversely to the major radius in a tokamak, the resulting Larmor radius of a given particle will increase as it nears the outer walls. While the guiding center approximation has been assumed appropriate, differences in the guiding center vs. full orbit representation may have noticeable effects on fast ion position and losses. This may be more pronounced in low aspect ratio tokamaks where the magnetic field gradient is steeper. Such effects are examined for energetic particles within National Spherical Torus Experiment – Upgrade discharges. |
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JP11.00070: Bayesian Optimization of Direct-Drive Inertial Confinement Fusion Simulations Brittany Callin, William T Trickey Inertial confinement fusion (ICF) is a form of controlled nuclear fusion where deuterium-tritium (DT) fuel is compressed to fusion densities and pressures via ablation of the surface of the DT capsule. In ICF experiments, demonstration of sufficient energy gain remains the key obstacle for commercially viable fusion-energy. ICF experiments are expensive and incredibly complex, leading to only a limited number of experiments being run each year. For this reason, state of the art radiation-hydrodynamics simulations are employed alongside experiments to examine a range of design parameters. This allows a wide variety of design spaces to be explored while minimizing cost and time. One of the most well established approaches to ICF as a possible fusion-energy source is direct-drive ICF. In this project the laser pulse for direct-drive ICF was modeled and optimized. Optimization is an attractive approach to ICF parameter spaces because it allows rapid and intelligent exploration of complex design spaces that are difficult to traverse manually. Specifically, Bayesian optimization was used to optimize the laser pulse. |
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JP11.00071: Survey Spectroscopy in the Large Plasma Device Kian Orr, Phil Travis, Troy Carter Survey spectroscopy is used on the Large Plasma Device (LAPD) to determine plasma impurities like carbon, as well as plasma parameters, namely electron temperature and density. We used an OceanInsight survey spectrometer to collect spectral data over a range of operating conditions. To visualize this spectral data, a graphical user interface that produces live updates is created in conjunction with a server to communicate between the spectrometer and the LAPD control room. A new LaB6 plasma source with a graphite heater has been installed on LAPD — unsurprisingly carbon emission is observed in the data. The ability to track carbon impurities is a valuable diagnostic on the plasma and the health of the plasma source and graphite heater. We have compared observed spectral data from several species with predictions using the ColRadPy1 collisional-radiative solver. The comparison between the observed and ColRadPy-produced spectra provides a method to confirm electron temperature and density measurements, and may allow independent measurements of these quantities using line-ratio information from the experimental data. Results from these comparisons will be presented and prospects for survey spectroscopy as a diagnostic tool for LAPD will be discussed. |
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JP11.00072: Using Collective Thomson Scattering to Characterize Velocity Distribution Functions of non-Maxwellian Plasmas Bryan Foo, Derek B Schaeffer, Peter V Heuer Electron and ion velocity distribution functions (VDFs) are important for understanding the dynamics occurring within nonlinear plasmas such as those of magnetized collisionless shocks. These VDFs can be measured in the laboratory with Thomson scattering diagnostics, but due to their non-Maxwellian nature, can be difficult to interpret with existing analysis tools which assume a Maxwellian plasma. We present an open-source software that can be used to fit Thomson spectra to arbitrary VDF models using a modular numerical scheme, which has been tested with synthetic Thomson-scattered spectra for robustness and error, using existing PlasmaPy code that handles strictly Maxwellian VDFs as a benchmark. Using an MCMC sampler, we were able to estimate the error and fit confidence for extracted plasma parameters. We find that when applied to commonly seen non-Maxwellian VDFs such as kappa distributions or supergaussians, the Maxwellian algorithm fails to accurately extract plasma parameters such as the density and equivalent temperature, while the new algorithm results in more accurate extracted plasma parameters and fitted VDFs if the correct VDF model is chosen. |
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JP11.00073: Measuring Ion Temperature from Thomson-Scattered Spectra of Non-Maxwellian Velocity Distributions in Magnetized Collisionless Shocks Brandan I Buschmann, Derek B Schaeffer, Bryan Foo, Peter V Heuer Collisionless shocks are common features of many astrophysical systems and have been recently studied in scaled laboratory experiments by driving a laser-ablated piston plasma into a magnetized ambient plasma [1]. Diagnosing the electron and ion velocity distribution functions (VDFs) is crucial to understanding these systems, but the VDFs in collisionless shocks include multiple distinct ion and electron populations, making them highly non-Maxwellian. A key method for measuring these VDFs is Thomson scattering, but current Thomson analysis techniques usually assume the plasma is Maxwellian, which is a poor assumption in the case of collisionless shocks. Thus, we present a software pipeline for analyzing Thomson-scattered spectra of non-Maxwellian plasmas that inverts measured spectra to VDFs using a differential evolution fitting algorithm and a forward model for arbitrary VDFs. This pipeline is used to extract time-resolved ion heating across magnetized collisionless shocks in order to test theories of shock heating. The pipeline used in this analysis will build on and eventually be added to the open source PlasmaPy project. |
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JP11.00074: Investigation of Incident Ion Angle Distributions on LTX-β Surfaces via a Micro-trench Method Jhovanna Garcia, Shota Abe, Anurag Maan, Richard Majeski, Bruce E Koel LTX-β is a tokamak device that investigates the effects of using lithium-treated walls on plasma performance. Characterizing the incident ion angle distributions (IADs) at wall surfaces plays a significant role in advancing our understanding of plasma-material interactions (PMI) at the lithium surface and the collisionless scrape-off layer (SOL) potential structure. Measured IADs were used previously to verify the sheath potential structure at the DIII-D divertor surface [1]. Here, we fabricated micro-trenches on a silicon disc sample by using a focused ion beam (FIB) to measure the IADs. A sample manipulator including a holder attachment for the micro-trench sample was designed, fabricated, and installed on LTX-β. The micro-trench holder is equipped with a Langmuir probe situated near the sample surface for plasma parameter diagnostics, as well as a button heater and thermocouple to investigate temperature effects on liquid lithium PMI. Measured IADs were compared to ion trajectories calculated by an equation-of-motion model for different SOL and sheath potential assumptions. Using verified IADs, we then applied a Micro-Patterning and Roughness (MPR) code to calculate the erosion and ion shadowing effects on a 3D numerical surface of the LTX-β stainless steel wall obtained by confocal microscopy measurements [2]. |
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JP11.00075: Remotely Controlled Thrust Stand Calibration for Milli-Newton Plasma Thrusters Stepan Gorelenkov, Ivan Romadanov, Yevgeny Raitses We implemented a calibration system for a thrust stand which will be used for characterization of low-power Hall thrusters. These thrusters are designed for operation at low power levels of less than 200 W. They include a cylindrical geometry Hall thruster [1] and a wall-less Hall thruster [2], both generate a thrust at the level of a few mN. With the thrust to the thruster mass ratio of 1-10mN/kg accurate thrust measurement is not a trivial task. There are several requirements for the design of the thruster stand: high thrust resolution and sensitivity (~0.05 mN [2]), minimized thermal drift during the thruster operation and in situ calibration of the thrust stand. As the thruster is tested in a vacuum chamber, calibration must be performed remotely without the need to open the chamber. In this work, we will discuss how this, and the other challenges of the accurate and reliable thrust measurements are addressed for these low power Hall thrusters. |
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JP11.00076: Upgrading remote control capabilities of a DC discharge experiment Emaje Hall, Arturo Dominguez, Sherwin Trieu, Sean Hough Through years of development, the remote glow discharge experiment (RGDX) has become a leading educational tool. The use of a direct-current glow discharge tube is a visually attractive way to expose the general public to plasmas. The experiment consists of two electrodes in a glass tube containing air. As a voltage is applied to the electrodes, the air is broken down to a plasma. The tube is also surrounded by a set of Helmholtz coils designed to control the plasmas magnetic field. By accessing a URL displaying the RGDX controls and a webcam, users can remotely control in real-time these parameters: voltage, gas pressure, and magnetic field. In this poster, we examine how an updated web interface and electrode separation, a fourth parameter, was added. The software and hardware upgrades needed to get to a functional, movable electrode provides users the capability of performing more advanced studies of plasmas from their home computer. |
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JP11.00077: The first quasi-axisymmetric permanent magnet stellarator Mohammed Haque, Dominic Seidita, Xu Chu, Tony Qian, Michael C Zarnstorff Fusion energy has the potential to meet the world's demand for clean energy. The stellarator was first invented in 1951 as a potential device for fusion reactions. It uses external coils to generate a magnetic field as well as rotational transform to confine the fusion plasma in a toroidal region. Early stellarators had poor plasma confinement due to large neoclassical loss and MHD instabilities. With the development of more advanced design tools, modern stellarators have been optimized to minimize neoclassical loss (and to be MHD stable). Today, like Windlestien 7X, Stellarators have complex designs that make maintenance and access difficult. It has been proposed by Mike Zarnstorff, et. al.[1] that using planer coils and permanent magnets to generate a magnetic field can significantly reduce the difficulty in building a stellarator. A permanent magnet stellarator would make construction much easier, cheaper, provide us with more freedom for optimizing the magnetic field, make the design and construction modular, and would enable rapid prototyping. We are building the world's first quasi-axisymmetric permanent magnet stellarator(MUSE)[2] to demonstrate the feasibility of this approach for building optimized stellarators. |
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JP11.00078: Open Source Simulation Platform for Plasma Education Kimberly Hizon, Corey Dechant, Steven Shannon With plasma's many applications, there are great benefits to studying it. To physically produce a plasma, however, vacuum systems, gases, and a source of high energy are needed. By utilizing computational methods to model these plasma systems instead, resources, such as these, can be conserved. Zapdos1 is an open-source plasma code that employs finite-element method (FEM) and the Multiphysics Object-Oriented Simulation Environment (MOOSE) framework to simulate the transport of plasma species, the mean energy of electrons, and plasma potential assuming the electrostatic approximation. It does this by using a multi-fluid plasma model, treating the plasma as a fluid. By using principles found in Michael A. Lieberman's, "Principles of Plasma Discharges and Materials Processing, " we have developed a wide range of tutorials, template input files, and video demonstrations2 with cases from diffusion to electronegative plasmas. Being that Zapdos is open-source, the ability to learn about plasmas and construct customizable plasma models will be accessible to more students. With its ability to provide accessibility, convenience, and conservation of resources and time, Zapdos is a necessary resource that will serve as a catalyst to drive plasma exploration and learning. |
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JP11.00079: Measurement of Magnetic Field in Magnetic Reconnection Experiments Using Proton Radiographs coupled with an In-Situ X Ray Reference Abraham M Hollmann, William R Fox, Sophia Malko, Derek B Schaeffer, Gennady Fiksel Experiments at the NIF and OMEGA laser facilities are used to understand magnetic reconnection for the applications of laboratory astrophysics and fusion. At these facilities, a laser target interaction is used to produce two plasma plumes with reversed magnetic fields due to the Biermann battery effect. The collision of the two plasma plumes drives an interesting phenomenon known as magnetic reconnection where magnetic energy is stored in the cross section of the reversing magnetic fields and released in a sling-shot motion driven by the magnetic forces. Proton radiography with a mesh is used to measure the magnetic fields during reconnection by differencing proton deflection images (of 3MeV and 15 MeV produced by a fusion implosion) with the undeflected mesh image generated by x-ray imaging. The undeflected mesh image is a recent addition to magnetic reconnection experiments that yields increased precision for proton radiography and 2D topology of magnetic fields. These results measure the profiles of the magnetic field undergoing reconnection for comparison with simulations and previous experiments. |
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JP11.00080: Increasing Access to Computational Plasma Physics using the Gkeyll Simulation Framework Shreyas Seethalla, James Juno, Arturo Dominguez, Ammar Hakim High performance computing is a critical component of modern plasma physics research. Every aspect of plasma physics is utilizing supercomputers to tackle the most high impact problems in the field, from transport in fusion reactors to the dynamics of plasmas around compact objects like black holes and pulsars. However, many students lack access to tools and resources to learn how to use high performance computing resources, and the required computational plasma physics skills to write code to leverage these resources. Using the Gkeyll simulation framework, we have created a set of Jupyter Notebooks to introduce students to the entire simulation workflow, from code compilation to resource selection, to running simulations and analyzing their output, all in a pedagogical fashion. The tool's scientific focus is a common plasma physics problem: magnetic reconnection while providing an introduction to high-performance computing via a holistic overview of running simulations. It will also control the input parameters, initial conditions, boundary conditions, and computing resources requested. Using a deployment of this new educational tool on the Princeton Stellar cluster, we will demonstrate how this workflow provides a new means of introducing students to both computational plasma physics and high performance computing. |
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JP11.00081: Magnetic field sensitivity studies and construction of MUSE Dominic Seidita, Michael C Zarnstorff, Tony Qian, Djin Patch, Mohammed Haque, Caoxiang Zhu MUSE is a tabletop, permanent magnet stellarator which has been constructed at PPPL that has a quasi-axisymmetric magnetic field using simple coils. This work presents sensitivity studies of the magnetic field due to certain possible construction defects. These defects include correlated perturbations of the permanent magnet locations due to the magnet holders being misplaced, uncorrelated 'flipping' of permanent magnets which were placed backwards in their seats, and uncorrelated 'replacing' of permanent magnets when permanent magnets of a different size than the intended size are placed in a given location. The severity of these perturbations are analyzed to determine which types of errors pose the greatest risk to the construction of MUSE. Additionally, insights from the construction of MUSE and analysis of whether these perturbations were successfully avoided are presented. |
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JP11.00082: Particle-in-cell simulations and experimental design study of energy modification of a charged particle beam incident on a region of inhomogeneous radio frequency electric field Ludomil Wojtkowski, Autumn Fox, Mya Schroder, Osias Salem, Nathaniel K Hicks Charged particles incident on a region of space in which a radio frequency (RF) electric field exists that grows in strength in the direction of incidence and varies periodically in time may experience a ponderomotive force opposite to the direction of incidence. This may cause the particles to be reflected back toward their origin; examples include the Paul trap [1], the RF mass spectrometer, and the Multipole Plasma Trap [2]. Such devices are usually considered to operate in an adiabatic regime, in which the outgoing kinetic energy is unchanged after reflection. However, it is also possible to impart a net gain in the average kinetic energy of an ensemble of particles in an incident beam, by deliberate choice of the RF electric field parameters (e.g. frequency; RF voltage; electrode geometry). The adiabatic and non-adiabatic cases of various charged particle beams interacting with RF multipole electric fields are studied here via particle-in-cell (PIC) simulation using the Vsim 11 software package [3]. Along with RF electrodes and charged particle emitters, a retarding field energy analyzer is added to the model to simulate experimental observation of the energy distribution of the outgoing beams. The PIC simulations serve as the basis for an experimental design in which electron and ion beams are directed at an array of RF electrodes (driven at ~10 MHz for ions, and ~100 MHz for electrons), and the reflected (and transmitted) energy distributions are measured. The inclusion of a multicusp static magnetic field is also investigated, for its role in enhancing electron reflection. |
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JP11.00083: Constrained Optimization Methods in DESC Patrick S Kim, Rory Conlin, Daniel W Dudt, Dario Panici, Egemen Kolemen Stellarators require careful optimization of their three-dimensional fields to achieve desirable properties for the magnetic equilibrium and coils. Traditionally, this problem is solved using unconstrained optimization methods where both the desired properties and equilibrium constraints are combined into a single objective function. In this work, we implement constrained optimization methods into the new DESC stellarator code [1-4]. This allows the optimizer to simultaneously decrease the objective function while further satisfying the equilibrium constraints at each successive step. This procedure is more computationally efficient, robust, and may avoid some local minima. In contrast, in an unconstrained, multi-objective approach, the optimizer must satisfy the equilibrium constraints at each step, which can slow convergence and may lead to the Maratos effect. Finally, using constrained optimization methods prevents the optimizer from over-penalizing inequality constraints, and can lead to discovering new optimized equilibria. Example equilibria from both methods are presented, with objectives including quasisymmetry, magnetic well, and turbulent heat flux. |
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JP11.00084: A Confocal Laser-Induced Fluorescence System for Measurements of the Velocity Distribution Function in ExB Plasma Sources Jacob A Kiviat, Ivan Romadanov, Yevgeny Raitses Laser induced fluorescence (LIF) is a nonintrusive diagnostic technique which can be used for obtaining velocity distribution functions (VDF) of ions and neutrals based on their Doppler shift [1]. Conventional LIF optical setups have the beam injection path perpendicular to the emission collection path. This perpendicular system inhibits the usage of LIF as a diagnostic in systems surrounded by solid walls, like many applied plasma devices such as plasma or ion sources (e.g. Hall thruster). Confocal LIF systems have been developed to overcome this issue, but a tradeoff has been lower spatial resolution. However, recent confocal systems have achieved a millimeter-scale spatial resolution, which is close to that of a conventional LIF system [2-3]. Here, we report experimental results from an alternative confocal LIF system that utilizes a pair of axicon lenses [4]. We characterized the optical system and found an ion VDF in argon plasma. |
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JP11.00085: Chemical Characterization and Sputtered Ion and Deuterium Retention Measurements of Lithium and Boron Coatings Exposed to Low-Energy Deuterium and Helium Ions Braden T Moore, Shota Abe, Evan T Ostrowski, Bruce E Koel Lithium has been shown to increase energy confinement and allow for stable plasma discharges in tokamaks, which makes it a candidate material for Plasma-Facing Components (PFCs). Boron injections are planned for NSTX-U and have been shown to lower impurity levels and reduce the H-mode power threshold leading to better plasma performance. Simulations on simultaneously lithiated and boronized surfaces show that chemical interactions between lithium and boron affect deuterium retention and the plasma-material interactions [1]. Our experiments used a Sample Exposure Probe (SEP), an ultrahigh vacuum suitcase enabling sample transfers between a Sample Exposure Station (SES) and surface analysis chambers where the surface can be further modified using ion irradiations and analyzed using surface analysis techniques [2]. Both boron and lithium vapor deposition sources were constructed and attached to the SES to produce high-purity lithium and boron coatings on candidate PFC samples attached to the SEP. Lithium and boron coatings were exposed to low-energy deuterium and helium ions. Sputtered species were directly measured using a mass spectrometer, and Temperature Programmed Desorption (TPD) was used to measure deuterium retention. X-ray Photoelectron Spectroscopy (XPS) and TPD were performed before and after ion exposure to determine chemical composition changes of the coatings. [1] F. J. Domínguez-Gutiérrez, et al., J. App. Phys. 123, 195901 (2018). [2] A. Maan, et al., Rev. Sci. Instrum. 91, 026104 (2020). |
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JP11.00086: Fabrication of Low-Density Aerogels for IFE Applications Sebastian C Cypert, Wendi Sweet, Fred Elsner, Nina Langley, Eduardo Marin, Jarrod Williams, Grayson Lovelace, Ethan J Frey Low-density GA-CH and GA-CD aerogels (<50 mg/cc) have quite promising properties for use in Inertial Confinement Fusion (ICF) targets at NIF and OMEGA; the low density and low Z make it a prime candidate for foam liners. Materials like resorcinol formaldehyde (RF) and divinylbenzene (DVB) that have been previously fabricated in the droplet generator can only be fabricated at higher densities. Physical properties of GA-CH and the required fabrication process conditions have been a major hurdle in making GA-CH shells and beads in the droplet generator, an approach that can mass-produce capsules for possible applications in Inertial Fusion Energy (IFE). This paper will look at two ways of making foam beads and shells from GA-CH: machining and droplet generator. To date, GA-CH shells have never been fabricated, and beads have only been machined individually. This work describes the first attempts at making beads and shells in the droplet generator, including modifications made to the droplet generator and the quality of shells made from the process. Shells made with separate machining and leaching process will also be discussed, including optical quality and foam shrinkage. Ultimately, we will compare the benefits of each method of production. |
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JP11.00087: Measurement of mode coupling in the dust acoustic wave Mabel Penaherrera, Etthan Tedros, Jeremiah D Williams Most naturally occurring plasmas contain small particulate matter (dust) and the presence of this third charged species leads to a plasma system that is notably more complex than the traditional plasma system. These systems, known as dusty plasmas, support a wide range of physical phenomena, including a low-frequency longitudinal wave mode known as the dust acoustic wave. This wave has been observed to simultaneously support a number of wave modes and it is possible to preferentially drive a single mode. Further, previous measurements have suggested turbulence may be observed during the transition from a driven wave mode to the naturally occurring mode. This poster will present the results of a detailed study looking at this transition and the coupling of select wave modes. |
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JP11.00088: Gyrokinetic Simulation of the Edge in LTX-β Using Gkeyll in 1 and 2 Dimensions Griffin Trayner, Manaure Francisquez, Anurag Maan, Noah R Mandell, Gregory W Hammett, Ammar Hakim Lithium coated plasma-facing walls can significantly reduce plasma recycling, yielding an operating regime with a hot edge and essentially flat temperature profiles in the core. Lithium-coated walls are studied in the Lithium Tokamak Experiment (LTX-β), a tokamak with a 40 cm major radius, 0.3 T toroidal field and $I_p=135$ kA. In order to establish a connection between the flat temperature profiles with a hot edge and a reduction in wall recycling, we require estimates of the plasma fluxes to the wall. Most scrape-off layer (SOL) simulations use fluid models that are not rigorously valid in the hot, collisionless interior of LTX-β. Furthermore, they may lack important mirror trapping effects that can affect the plasma profiles in this region. We therefore employ the gyrokinetic solver in the Gkeyll code to study the SOL, carrying out 1D simulations to understand the parallel dynamics and the impact of mirror forces in the LTX SOL. We compare these 1D simulations with adiabatic electron simulations, and also discuss 2D simulations which we employ to study the impact of drifts and to provide better initial conditions for 3D simulations. This work can help us better understand properties of a lithium-walled machine and improve our ability to predict its performance in the future. |
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JP11.00089: Temperature measurement of Warm Dense Matter using Streaked Optical Pyrometry Joseph A Vargas, Valeria Ospina-Bohorquez, William R Fox, Derek B Schaeffer, Mathieu Bailly-Grandvaux, Xavier Vaisseau, R Fedosejevs, Joao J Santos, Brooklyn Frances Kraus, Sophia Malko The study of Warm Dense Matter (WDM) is of great interest for both inertial confinement fusion and fundamental science. WDM is a type of plasma that exists in a temperature range from 10-100 eV and has a density around the same magnitude or higher than the solid state. A common challenge to all plasma experiments is being able to accurately measure these physical conditions, however, is of the utmost importance for benchmarking hydrodynamic simulations. Here we report on a WDM target characterization using Streaked Optical Pyrometry (SOP). The experiment was performed at the ALEPH laser facility, where WDM conditions were generated by irradiating a thin 1 μm carbon foil with a heater laser of 500 fs pulse duration and 1 J of energy, yielding 5x1015 W/cm2 on target. |
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JP11.00090: The kink instability in force-free twisted flux tubes Natalie Rugg, Jens F Mahlmann, Benjamin Crinquand, Anatoly Spitkovsky This work investigates under which conditions a straight, highly magnetized flux tube with fieldlines frozen into perfectly conducting boundaries develops a kink instability when twisted. Running a force-free electrodynamics code, we conduct numerical experiments to vary the parameters with the most impact on stability: flux tube height and the amount of twist. Comparing the growth rate of the kink mode to analytical models, we then constrain an instability criterion. We identify a threshold of twist below which a flux tube remains in equilibrium. Past this threshold, progressive increases in the amount of twist cause the kink instability to develop sooner and grow faster. The force-free plasma flux tubes of this simulation have applications to high-energy, high-magnetization astrophysical phenomena, such as magnetar flares and accretion disc coronae variability. |
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JP11.00091: A Nomarski Interferometer for Electron Density Measurement in Atmospheric Pressure Plasma Fengyan Zhang, Adam D Light Although it is more frequently applied in low-pressure or laser-induced plasma, interferometry has been used successfully to characterize atmospheric pressure plasmas [1]. We present the design of an interferometer for pulsed measurements of electron density in an atmospheric pressure plasma jet. Motivated by the setup simplicity and relatively low sensitivity to vibration, we employ a Nomarski (single-beam) interferometer. Since the phase shift is expected to be very small (1-100 microradians), we use lock-in detection with narrow bandwidth to recover the signal. At the first stage of development, we will send a continuous laser beam through an atmospheric plasma jet with modulating electron density at 10 to 20 kHz. We will present progress to date and details of the experiment setup. |
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JP11.00092: Exploring the formation and robustness of partially relaxed MHD states Matt Ketkaroonkul, Adelle Wright In this presentation, we explore the ‘ideal interfaces’ posited by Multi-Region Relaxed Magneto-hydrodynamics (MRxMHD), which are highly localized currents that partition the plasma into discrete volumes. We do so by analyzing the properties of such interfaces. For this, our analysis of the ideal interfaces is carried out through two methods. Our first method involves boundary layer theory to examine the local properties of ideal interfaces. Combined with the methods developed by Hahm and Kulsrud, this is used to assess the robustness of ideal interfaces under non-ideal effects, such as resistivity. |
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JP11.00093: Comparison of stability characteristics of different smoothness classes of MHD equilibria Nathaniel S Watkins, Adelle Wright We present a comparison of the stability properties of magnetohydrodynamic (MHD) equilibria characterized by different smoothness i.e., C^0, C^1, C^{\infty}, to examine whether there exist fundamental differences in the physical features of these states. Specifically, we use the Energy Principle to analyze how physical properties associated with contributions arising from smooth and non-smooth terms lead to stabilizing and/or destabilizing effects on steady state, magnetically confined fusion plasmas. |
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JP11.00094: Quench Analysis of High Field Superconducting Magnets Luke Payne, Yuhu Zhai Our research is focused on quench analysis of a No-Insulation High Temperature superconducting magnet, based on research done by Bhattarai et al. [Bhattarai et al. IEEE Transactions on Applied Superconductivity, vol. 26, no. 4, June, 2017]. We use the lumped circuit model to decrease the computational time needed to run our simulation on multiple pancake coils to calculate T, Rsc,Ic, Isc and V as a function of time after quench. Our goal is to understand what happens in a HTS magnet during quench to better understand safe operating procedures before using HTS in high field tokamak devices. |
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JP11.00095: Cost Analysis of High Temperature Superconducting Magnets for for Fusion and High Field Applications Rohan Lopez, Yuhu Zhai Superconducting magnet strands costs can be evaluated for different strand geometries and material ratios through a production scaling factor P. P depends upon the cost of raw materials and purchase data. This cost analysis is critical for the exploration and development of High Temperature Superconducting (HTS) magnets for magnetic fusion, MRI & NRI magnets, and high field research magnets. The cost indices of interest are $kg−1 ,$m−1, and $ kA−1 m−1. The target specs for analysis are 4-20 K (LHe or Gas He etc.) / less of 77 K (LN2), high fields (TF / OH - 15-20+ T), and a high packing factor (Je > 80-100 A/mm2 (ITER TF coil Je is < 17 A/mm2). |
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JP11.00096: Experimental Statistics of Taylor State Reconnection Ayla C Cimen, Kya M Butterfield, Michael R Brown We present the results from the Swarthmore Spheromak Experiment (SSX). In SSX, Taylor State plasmas are formed on both ends of our device and evolve to have a large aspect ratio flux conserver where $\ell/R \approxeq 10$. The plasmas approach each other at velocity $\sim 40 km/s$, each with density $n_e \approx 5 \times 10^{15} cm^{-3} $, proton temperature $T_i \approx 20\ eV$, and magnetic field $B \approx 0.5\ T$. At the mid-plane where the collision occurs, a He-Ne Interferometer measures line-averaged density, a 2D $\Dot{B}$-Probe Array measures magnetic field at 16 locations, and Ion-Doppler Spectroscopy is responsible for the measurement of proton temperature. With data from approximately 1000 shots, we present typical findings for density, $\Vec{B}$-field, and temperature evolutions. Included in our investigation are key statistical diagnostic relationships, namely between magnetic field orientation during reconnection and peak proton temperature. |
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JP11.00097: Optimizing Quasi-Poloidal Stellarators Alexander Ireland, Elizabeth Paul Stellarators offer several distinct advantages over tokamaks as magnetic-confinement fusion devices. Recent progress has been made in optimizing stellarators for quasi-axisymmetry (QA) and quasi-helical (QH) symmetry. However, quasi-poloidal (QP) stellarators have not been studied as thoroughly as QH or QA designs. QP symmetry indicates that the contours of magnetic field strength close poloidally, resulting in a variety of benefits: QP design promises steady-state operation with reduced bootstrap current, reduced orbit width, and increased E x B shear. This project utilizes the optimization software simsopt to find novel QP stellarator configurations. Additionally, we study the tradeoffs of QP symmetry with geometric constraints such as the aspect, elongation, and mirror ratio. |
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JP11.00098: Controlling the charge on dust particles using UV photo discharging Edward Cowles, Michael McKinley, Saikat Chakraborty Thakur, Edward Thomas
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JP11.00099: Understanding the spatiotemporal dynamics of plasma filaments at high magnetic fields via spatiotemporal image analysis David E Floyd, Stephen Williams, Saikat C Thakur, Edward Thomas Recent experiments in the Magnetized Dusty Plasma eXperiment (MDPX) at Auburn University have shown that capacitively coupled, radio frequency generated plasmas form different kinds of filamentary structures when exposed to a high enough magnetic field (B > 1 T). Essentially, these filaments are non-uniformities in the plasma, that appear as bright vertical elongated structures parallel to the magnetic field, formed between two parallel plate electrodes. When observed from the top, they can have different shapes such as circular, s-shaped two-arm, and three-arm or four-arm spirals, indicating that these structures might be azimuthal eigenmodes of some underlying instability mechanism. A host of spatiotemporal dynamics have been identified including spinning about a stable axis, global motion due to filament-filament interaction, filament merger and changing shapes from one to the other. Here we will use different image analysis techniques to understand the details of the spatiotemporal variations of these filaments. This will help us understand the fundamental physics that lead to structure formation and the ensuing dynamics. |
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JP11.00100: Identification of W II spectral lines for tungsten erosion measurements using high-resolution ultraviolet spectroscopy Noah S Kim, David A Ennis, Stuart D Loch, Curtis A Johnson, Tomas Gonda The potential of tungsten as a plasma facing component in future nuclear fusion devices is dependent on erosion rates when exposed to high-temperature plasmas. A tungsten-tipped Langmuir probe for simultaneously sourcing W and measuring electron temperature and density is inserted into the Compact Toroidal Hybrid (CTH) experiment for erosion studies. Tungsten emission is detected by a high-resolution spectrometer optimized for ultraviolet wavelengths used to investigate critical phenomena such as the effect of metastable states and re-deposition rates. Inserting the tungsten-tipped probe to varying depths in CTH provides a method for observing changes in the spectral intensity due to different plasma conditions. It is also necessary to acquire spectra with different probe tip materials to distinguish background spectral lines. Experiments utilizing CTH have accumulated high-resolution spectroscopic data for tungsten, molybdenum, and tantalum to identify spectroscopic lines of interest in the ultraviolet region (200-400 nm) for neutral tungsten emission. Ongoing analysis of singly ionized tungsten emission has preliminarily identified over 30 W II emission lines of potential interest for erosion measurements. |
Author not Attending |
JP11.00101: Design and characterization of a low-cost Atmospheric Pressure Plasma Jet (APPJ) Matthew Unden, Saikat Chakraborty Thakur, Edward Thomas Atmospheric Pressure Plasma Jets (APPJs) belong to the class of high pressure, room temperature plasma production mechanisms that have a large set of biological applications by killing harmful pathogens (eg. salmonella on food surfaces) or altering the surface chemistry of the target material (eg. seeds, chicken feathers). High frequency pulsed DC discharges are typically used to control the corresponding plasma characteristics. However, localized applications of a pencil like APPJ discharge and the high cost of the controlling electronics prevent scaling up of the helpful plasma application set ups. Here we built and studied an argon based APPJ, ionized by high frequency pulsed DC, AC, and/or RF power under variable electrode spacings, neutral gas flow rates and ionization voltages to determine the best combinations with the aim of producing a relatively inexpensive way of delivering room temperature, atmospheric pressure plasmas. This will then allow for the scaling up of such a system to be used on larger surface areas. |
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JP11.00102: Formation of Filaments and Nested Surfaces in Microgravity Dusty Plasma Emerson Gehr, Evdokiya Kostadinova, Marlene Rosenberg, Peter Hartmann, Jorge Carmona Reyes, Lorin S Matthews, Truell W Hyde This research examines the structure and spacing of particles within microgravity dusty plasma clouds using video data from the PlasmaKristall-4 (PK-4) apparatus onboard the International Space Station. The analysis focuses on experiments where gas pressure and current were varied to achieve different plasma conditions, which in turn affect the structural properties of the dust clouds. We analyze videos from a central region of the cloud as well as 3D-scans of the entire cloud. Positions of the particles in each video frame are obtained using particle tracking software, and then used to calculate pair correlation functions that show the probability of finding a particle a certain distance away from another particle. The obtained pair correlations reveal differences in the mean interparticle separation as a function of location in the cloud, gas pressure, and discharge current. We find that particles tend to organize in filamentary structures at the small scales, while forming nested spheroid shells at large scales. While particles within filaments are strongly coupled, suggesting crystalline order, the interaction of particles across filaments is liquid-like. These results provide evidence that the structures observed in the PK-4 have unique liquid crystalline properties. |
Author not Attending |
JP11.00103: Study of Mode-Coupling Instabilities in a Plasma Crystal Using N-body Simulations Jorge A Martinez Ortiz, Rahul Banka, Calvin Carmichael, Katrina Vermillion, Bryant Wyatt, Lorin S Matthews, Truell W Hyde Experimentally observed melting of two-dimensional dusty plasma crystals is theorized to occur due to the mode-coupling instability (MCI). The coupling between the transverse and longitudinal wave modes of single-layered crystalline structure occurs largely due the interaction of dust grains with ion wake-fields, non-homogenous regions of positive charge that form downstream of each grain. Whereas MCI-induced melting is widely studied in experimental settings, the study of ion wakes predominantly relies on numerical simulations. We present our work on reproducing MCI melting of a plasma crystal in real time using a GPU-accelerated N-body simulation that implements a simplified point-charge model of the ion wake where the wake is allowed to vary dynamically. The simulation replicates the conditions inside of a GEC RF Reference Cell containing an argon plasma. The characteristics of the ion wakes as a function of plasma power, pressure, and grain separation are obtained from the numerical model DRIAD. We aim to provide a tool that can harness the versatility of computer models without sacrificing the interactivity of an experimental setup. Such a tool will facilitate the study of the interactions between ion wake-fields and MCIs. |
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JP11.00104: Electron Beam Injection Method for Determining Plasma Frequency and Electron Density Geoffrey M Pomraning, Paul M Bellan A method for the direct measurement of plasma frequency from a detected electron beam in the Caltech ice dusty plasma experiment [1] is being investigated. Adapting a method of Shirakawa [2], an electron beam will be generated from an emissive tungsten filament and injected into a weakly (10-6) ionized plasma with cold (~190 K) neutrals. This beam should generate electron plasma waves excited by the two-stream instability. The waves would then be detected by a separate receiving probe in the plasma. This method overcomes several limitations of the conventional Langmuir probe method (e.g., thin-film deposition, uncertain calibration), and removes the dependence on plasma ionic composition for computing electron density. The probe is under construction and results will be presented at the meeting and compared to other methods. |
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JP11.00105: Measuring Terahertz Radiation in Laboratory Simulations of Astrophysical Plasma Jets with Field-Effect Transistors Joshua Pawlak, Paul M Bellan Experiments simulating astrophysical plasma jets at Caltech have densities of 1021 to 1022 m-3, so the electron plasma frequency falls in the low terahertz regime. Because the upper hybrid frequency is dominated by the electron plasma frequency in this experiment, a strong terahertz radiation emission is expected from electromagnetic wave excitation at the upper hybrid resonance layer. However, measurement of this radiation is challenging because of the “terahertz gap” in detection technology, such that there is a dearth of suitable detectors. |
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JP11.00106: Production and detection of solvated electrons with atmospheric-pressure plasma jets John T Lê, Adam D Light At the plasma-liquid interface, plasma electrons can dissolve in a liquid solution to form solvated electrons. Solvated electrons are a strong reducing agent and have applications in chemistry and plasma medicine. The Bartels & Go groups at the University of Notre Dame have produced and detected solvated electrons at a plasma-liquid interface using a direct DC discharge. However, little work exists on the production of solvated electrons by remote sources such as atmospheric pressure plasma jets (APPJs). We plan to implement the total internal reflection geometry of Rumbach, et al. [1] to measure solvated electron concentration produced by APPJs. Laser light is reflected off the underside of the water-plasma interface to probe the ~10nm layer in which electrons are solvated and lock-in detection is used to recover the modulated absorption signal. We present our design, preliminary measurements, and possible diagnostic improvements (e.g., cavity enhancement) in detecting and producing these solvated electrons with jet sources. |
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JP11.00107: A new emissive probe circuit for the EPaX experiment at the University of San Diego Aaliyah Marshall, Lena Belvin, Gregory Severn A new low temperature plasma experiment is coming online at the University of San Diego (USD) that attempts to explore (measure) internal sheaths in electronegative plasma, called the Electronegative {PlAsma Sheath EXperiment, or EPaX. Plasma potentials are to be measured with emissive probes built for the new experiments. New emissive probe circuits must also be built, and instead of reproducing the existing circuit in use at USD, we attempt to change the design from a current controlled bipolar junction transistor (BJT) based design [Yan, et al. Rev. Sci. Instrum. 67 4130 (1996)] to a voltage controlled MOSFET based design, with a view to achieving significant simplification and improved noise reduction. The nominal operating parameters for our current circuit is approximately 1.2 ma of emission for 300 ma of heating current, for a 6mm long tungsten filament that is 25.4 $\mu m$ in diam. We compare the two circuits for for experiments performed in weakly collisional (λmean-free-path>>λD), low pressure (Pneutral ≤ 1 mTorr), low temperature (kTe of order 1 eV), single ion species Ar plasma. |
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JP11.00108: Does presheath ion flow affect electron density measurements for Langmuir probes near boundaries? Mohammedali Mohamed, Adrian Woodley, Gregory Severn It has recently been shown that Langmuir probes (LPs) measure an unphysically positive plasma potential in the presheath of low temperature plasma, near conducting boundaries at which ion rich sheaths form [Li et al., Plasma Sources Sci. Technol. 29 (2020) 025015]. It has been argued heuristically that the difference between plasma potential profiles measured by LPs and emissive probes (EPs), in the presheath, is related to ion flow caused by sheath formation. We present experimental evidence that the electron density is also overestimated by standard analysis in the presheath, that the two anomalies are interrelated, having to do with ion flow near the boundary where an ion rich sheath forms. We attempt to estimate the sheath expansion due to ion flow using the constraint of quasineutrality in the presheath. These experiments are performed in weakly collisional (λmean-free-path>>λD), low pressure (Pneutral ≤ 1 mTorr), low temperature (kTe of order 1 eV), single ion species plasma, where the feedstock gas is Ar or He or Xe or Kr. |
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JP11.00109: Application of Schlieren Imaging technique for plasma flow and Mask Airflow Connor Q Belt, Surabhi Jaiswal Schlieren imaging is a powerful technique to visualize airflow patterns in open atmosphere. In this work, a single mirror schlieren optical system is applied to visualize the flow pattern of two different scenarios. We have checked the effectiveness of different types of masks: cotton cloth, face sleeve (gaiter mask), surgical, and KN95. Using schlieren imaging, the refractive index of the air jet leaving the mouth can be visualized non-intrusively, giving a clear picture air flow pattern from these masks. Data from this experiment showed promising results with differences in the way the air jet was dissipated into the surrounding atmosphere. Utilization of this technique to measure an atmospheric pressure plasma jet flow pattern when interacting with open atmosphere will also be presented. Preliminary results of gas shielding on the plasma jet behavior will also be discussed. These results have implications for a number of technological applications of plasma. |
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JP11.00110: Study of a Supersonic, Magnetized Plasma Jet with a Magnetic Probe Array and High Frequency Wave Probe Christopher M Lamb, Byonghoon Seo Presented is a method to observe magnetic field characteristics in a three-dimensional volume as well as high frequency waves generated by a pulsed plasma source. This source will produce a plasma jet that exhibits instabilities and magnetic reconnection [1] inside Embry-Riddle’s two meter long, cylindrical plasma chamber. Magnetic reconnection is a process by which a portion of magnetic field energy is transferred into kinetic or thermal energy of plasma [1]. By observing the topology of the magnetic field at distinct locations over many pulses with the magnetic probe array, a three-dimensional vector space can be constructed for the plasma as it evolves over time. The magnetic field observations will be performed with a calibrated magnetic field probe array (MPA) as described in Ref. [2]. Design and calibration methodology for the high frequency array is motivated from instruments described in Ref. [3]. By interpreting these data over system parameter variations, the construction of an empirical model will be suggested for the plasma behavior. This study will investigate fundamental plasma physics, such as the drivers, effects and patterns of reconnection and may lead to a better understanding of ion heating, dynamics of the corona of our star and reconnection-preheated magnetized inertial fusion. |
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JP11.00111: Direct measurement of density using Abel transform of Refracted Enhanced Radiograph (RER) in ICF capsule implosion at the National Ignition Facility Brendan McCluskey, Alexandre Do, Eduard L Dewald, Otto L Landen, Chris Weber X-ray Refraction Enhanced Radiography (RER) experiments have been developed1,2 recently at the National Ignition Facility to give a direct measurement of density gradients at both fuel-ablator interface and ablation front in indirect drive capsule implosions. While they provided quantitative measurement of mix-width1 and interface trajectory2, the determination of the spatial and time resolved density is done using a forward fit model with high uncertainty. An analytical Abel transform model has been demonstrated3, which allows for the direct deconvolution of the density from the RER data. Thanks to the high signal-to-noise ratio (> 20) and high resolution (< 6 µm) of the most recent dataset, we have been able to, for the first time, apply this model to obtain a direct measurement of the time and spatial variation of the capsule limb density. |
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JP11.00112: Calculation of footprints of magnetic field lines in the two-mode nonresonant stellarator divertor Alkesh Punjabi, Mia Williams, Valerio Palamara, Jaron Scott, Halima Ali, Allen H Boozer There are three parameters in the Hamiltonian function for the trajectories of magnetic field lines in nonresonant stellarator divertor. They are called the shape parameters. They control the elongation, triangularity, and the sharpness of edges on the outermost confining magnetic surface in nonresonant divertor. When we set the parameter that controls the sharpness of edges on the outermost surface equals to zero, we get a two-mode nonresonant divertor. The outmost surface in two-mode divertor is at r = 0.8947b where b is minor radius in the poloidal angle = 0 in the poloidal plane defined by toroidal angle of the period = 0. We start the field lines just outside the outermost surface in this poloidal plane. We use the method for calculation of full 3D magnetic turnstiles developed in [[A. Punjabi and A. H. Boozer, Phys. Plasmas 29, 012502 (2022)]. The intersection of the magnetic turnstiles with the wall gives the magnetic footprint on the wall. It appears that (1) The loss-times of field lines in two-mode divertor are quite large, (2) The footprints have fixed locations on the wall and the sizes of footprints are considerably small compared to the footprints in nonresonant divertor [[A. H. Boozer and A. Punjabi, Phys Plasmas 25, 092505 (2018); A. Punjabi and A. H. Boozer, Phys. Plasmas 27, 012503 (2020) (Editors Pick)]. This work is supported by DOE OFES grants DE-SC0020107 and DE-FG02-07ER54937 to Hampton University, and DE-FG02-03ER54696 to Columbia University. Research used resources of the NERSC, supported by the Office of Science, US DOE, under Contract No. DE-AC02-05CH11231. |
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JP11.00113: Depositing Lithium Films to Simulate ICF Reaction Products Chunsun Lei, Andrew Hotchkiss, Andrew L Martin, Adam Brown, Mark E Yuly, James G McLean, Stephen J Padalino, Chad J Forrest, Thomas C Sangster, Sean P Regan A possible future experiment using Inertial Confinement Fusion (ICF) to measure low-energy light-ion nuclear cross sections has been simulated using the SUNY Geneseo Pelletron to activate a thin lithium target which was then rapidly evaporated, trapped, and detected. This experiment required a lithium film to be deposited in a vacuum of approximately 10-5 Torr onto the surface of a thin tungsten foil. The films were produced by heating natural lithium pellets to 400 °C in a stainless-steel boat through which 20 A of current was passed. The evaporated lithium was contained inside a stainless-steel “house” inside the vacuum chamber, with a small opening on the top that allowed the lithium to reach the tungsten foil. The vacuum chamber was in an argon-filled glove bag which allowed the films to be briefly removed and handled since lithium reacts vigorously with oxygen and water vapor. |
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JP11.00114: An Experiment Simulating the Production, Capture, and Detection of 8Li from an ICF Implosion Andrew L Martin, Adam Brown, Chunsun Lei, Andrew Hotchkiss, Mark E Yuly, James G McLean, Stephen J Padalino, Chad J Forrest, Thomas C Sangster, Sean P Regan Inertial confinement Fusion (ICF) is a possible tool for measuring light-ion nuclear cross sections. One way to do this might be to trap and detect the radioactive decays of the product nuclei produced using a doped target capsule. Some of the highest yield light-ion reactions that could be studied using this technique are 6Li(t,p)8Li and 9Be(t,α)8Li, both of which produce 8Li. In order to simulate this method, a natural lithium film was deposited onto a tungsten substrate, which was then activated via the 7Li(d,p)8Li reaction using the SUNY Geneseo Pelletron accelerator. A current pulse of up to 1000 A was discharged through the tungsten raising its temperature to as high as about 1500 °C in less than a few milliseconds, causing the lithium to rapidly evaporate and produce a gas of neutral lithium atoms which then travelled outward and stuck to the aluminum getter detector foil of the Short-Lived Isotope Counting System (SLICS). This phoswich detector was used to identify beta particles and count in situ the 840 ms beta decay curve for 8Li as a function of time in order to estimate the efficiency of SLICS for trapping and detecting ICF reaction products. |
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JP11.00115: Dimensionality Effects on Laser-Accelerated Ions in 1D, 2D, and 3D Particle-in-Cell Simulations Lillian Daneshmand, Joseph R Smith Due to the high computational cost of 3D particle-in-cell (PIC) simulations, lower dimensional 2D or 1D simulations are commonly used instead to model ultra-intense laser-matter interactions. However, lower dimensional simulations do alter interactions in non-trivial ways due to various simplifications. This work studies the effects of dimensionality in PIC simulations on laser-accelerated ions with a series of 1D, 2D, and 3D simulations over a wide range of laser intensities (1018 – 1021 W/cm2). We compare multiple observables from the interaction, including maximum proton energy, laser-proton energy conversion efficiency, and accelerating field strength for these simulations. This work aims to isolate patterns across these variables and intensities between different dimensionalities. |
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JP11.00116: Energy dissipation by kinetic Alfven waves in sheared magnetic fields Kai Van Brunt, Abtin Ameri, Nuno F Loureiro Phase mixing of plasma waves leads to the evolution of increasingly smaller-scale perturbations, eventually leading to viscous or resistive dissipation of energy (Chen 2021). This has been suggested as a potential cause of solar coronal heating, though the details of the exact mechanisms involved are still unclear. We examine the effect of sheared magnetic fields on the phase mixing of Alfven waves, which increases their wavenumber transverse to the magnetic field, and so transforms them into kinetic Alfven waves that play a large role in electron heating. An ideal MHD model displays singularities at resonant Alfven points; thus, to investigate these phenomena, we incorporate finite ion Larmor radius effects into our gyro-RMHD model, allowing us to resolve the behavior of the plasma at those resonant layers. |
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JP11.00117: PIC-simulation of ultra-intense laser plasma interaction with shaped silica microtargets Hayden Beatty, Joseph R Smith, Enam Chowdhury Mass limited targets (MLT) in laser plasma interaction (LPI) is a reliable pathway to achieving warm and hot dense matter (WDM/HDM) states. The effects of ultra-high intensity laser light on various geometric arrangements of silica microspheres and cubes as MLT were investigated using 2D EPOCH particle-in-cell code. Multiple target configurations were used, where the laser, with 1018 W/cm2 or 1020 W/cm2 peak intensity, 400 nm wavelength, 40 fs pulse duration and a 1 µm beam waist radius, is focused onto a collection of targets. Initial conditions were charge-neutral and room temperature (300 K). Species were set to field ionize using a semi-classical tunneling ionization model and release electrons in strong accelerating fields. For all configurations, the simulations were carried out up to 400 fs. Comparison of single versus multiple target cases show that targets not directly hit by the laser exhibit different charged particle dynamics. At 1018 W/cm2 intensity, uniform electron heating was observed in the indirectly heated targets when the laser is focused onto the middle target only. Ionization of adjacent spheres with minimal dispersion is also demonstrated. At 1020 W/cm2 intensity, jet-like patterns of ejected charged particles are observed in multi-target configurations. |
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JP11.00118: Training Neural Networks on Synthetic Data for Target Normal Sheath Acceleration Thomas Y Zhang, Pedro Gaxiola, Joseph R Smith, Chris Orban Neural networks and other machine learning algorithms are beginning to be used in ultra-intense laser physics. An important concern is determining the minimum amount of data points needed for a neural network to be a viable approximation function because many laser systems are highly limited in how many shots per day they can operate. By using synthetic data based off of a model proposed by Fuchs et al. 2006, this paper explores the performance of a neural network with one hidden layer. When trained on datasets of varying sizes and for various numbers of epochs our work suggests that a minimum of 20000 data points are needed and that at least 30 epochs are needed to make a viable neural network that can estimate the max and average proton energies at a relative error below 10% and the total proton energy at a relative error below 20%. The results of this study can potentially be applied to training neural networks on real experimental datasets. A future direction for this research will be to train networks on a non-uniformly sampled parameter space in a way that is similar to how a real laser system would collect the data. |
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JP11.00119: Optimizing stellarators for better equilibria through the addition of phyiscs objectives to DESC Kaya E Unalmis, Daniel W Dudt, Rory Conlin, Dario Panici, Egemen Kolemen Stellarators require optimizing relevant quantities to design magnetic field configurations that admit desirable equilibria. Because complicated physics governs these quantities, more efficient algorithms and proxy functions prove essential for covering larger search spaces to find good equilibria. This work presents the addition of physics objectives and optimization parameters, such as the magnetic well, current profile constraints, and other particle confinement metrics to the DESC stellarator code suite [1-4]. These parameters measure equilibrium stability and plasma confinement, rendering them good figures of merit alongside symmetries for designing future stellarators. Implementing them in DESC – a code with automatic differentiation and fast gpu portability – improves our understanding of equilibria quality and allows optimizing for new equilibria which may better satisfy a larger set of objectives. |
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JP11.00120: Validity of the guiding-center approximation in various mirror and toroidal magnetic geometries Brook Hodgeman We investigate the validity of the guiding-center approximation for the magnetic mirror geometry and the axisymmetric tokamak geometry. Particle and guiding-center orbits are compared on the basis of the conservation of the azimuthal canonical angular momentum for magnetic mirror geometry and the conservation of the toroidal canonical angular momentum for axisymmetric tokamak geometry. |
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JP11.00121: Oxygen Monitoring in Xylene NTOF Detectors using Cosmic Ray Muons Aidan J Cheeseman, Joshua D Edelbach, Stephen J Padalino, Chad J Forrest At the Laboratory for Laser energetics, liquid xylene scintillators are used to perform neutron time of flight measurements. To improve the timing response of the detector, the xylene scintillator is oxygenated to decrease the decay time of the photo flash in the detector. This results in a faster detector which can be used to observe both primary and down scattered neutrons from an ICF burn. Over time, the oxygen concentration in the scintillator decreases through chemical mechanisms which are not yet well understood. As oxygen levels decrease, the detector response changes. Currently there is no method to determine the oxygen concentration in the sealed xylene detector. Thus, the detectors must be dismounted, emptied, refilled and remounted on the chamber every three months to ensure that it is working nominally. To mitigate this problem, cosmic ray muons are being used to produce signals in the detector. Changes in the muon signals can be used to determine the oxygen concentration level in the scintillator. When completed it is hoped that this method can be used to measure the oxygen level in situ reducing the need to dismount the detector, fill it and remount it. |
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JP11.00122: Rapid Vaporization of Activated Lithium for Detector Testing Johnathan Conway, Noah M Dauphin, Jessica M Dawson, Nicole M Lallier, Julia G Tufillaro, Carleigh B Wachtel, James G McLean, Stephen J Padalino, Chad J Forrest, Sean P Regan A system has been developed that uses high current to rapidly and consistently vaporize activated materials which have been coated onto a tungsten ribbon filament. This system will be used to test the Short-Lived Isotope Counting System (SLICS), which is being developed to measure the quantity of short-lived radioactive fusion products created in the Laboratory for Laser Energetics (LLE) Omega facility. SLICS is tested with simulated fusion products by capturing rapidly vaporized materials after activation with a beam in the SUNY Geneseo Pelletron accelerator. Using lithium as the target material for a deuteron beam, lithium-8 is produced and decays through beta emission with a half-life of 838 milliseconds. The vaporization system uses a thyristor to quickly discharge high-voltage capacitors, delivering 500-1000 Amps of current through tungsten filaments during a 5-15 millisecond time period. The maximum temperature of the filament, and therefore the vaporization rate of the lithium, depends on the capacitor voltage, ribbon geometry, and conductance of the coating. The relationships between these parameters are reported for uncoated tungsten filaments. |
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JP11.00123: A New Target-Manipulator Control Interface Connor T McDermott, Christopher J Ventre, Bryan J Diaz, Edward Pogozelski, Stephen J Padalino, Charlie G Freeman Using LabVIEW software and hardware, a new 3-axis 3-rotation target-positioning control interface has been constructed for the 15R end station of the 1.7 MV tandem Pelletron accelerator. The new system adjusts the position of the target within the 15R end station by remotely controlling three stepper motors in the X, Y, and Z directions. Two additional motors control rotation about the Theta (θ) and Phi (φ) axes. A sixth motor is dedicated to actuating the angular position of a detector. Previously, in order to control the manipulator, five switches were used to individually control the stepper motors. While these switches gave coarse control for the target and detector, the precise position of each motor was unknown. To improve the precision and accuracy of the control system, a Target manipulator LabVIEW system was designed at SUNY Geneseo. The LabVIEW system improves precision by allowing users to digitally input the desired position of the target and the detector with positional resolution of .001 mm and angular resolution of .01° then save those settings for future use. This will improve the reproducibility of the experimental configuration. In addition, the LabVIEW system includes limit indicators and locking mechanisms that prevent users from operating more than one stepper motor at a time which was not possible with the previous control system. Funded in part by the US Department of Energy through the Laboratory of Laser Energetics. |
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JP11.00124: Rutherford Backscattering Spectroscopy Analysis of MTW Debris Shields Vincent Picciotto, Yuki Watariguchi, Kevin Cerda, Charles G Freeman A set of debris shields used at the multiterawatt (MTW) laser at the Laboratory for Laser Energetics was analyzed using Rutherford Backscattering Spectroscopy (RBS). The debris shields consist of microscope cover slips that were placed over an objective in the MTW target chamber. The debris shields were positioned directly behind copper and tin target foils that were irradiated by the MTW laser. The irradiation of the target caused target material to be accelerated from the rear side of the foil and strike the debris shields at normal incidence. RBS analysis of the debris shields was carried out using ion beams from the SUNY Geneseo accelerator. The ion beams had energies of up to 3.0 MeV for protons and 4.5 MeV for alpha particles. The ions struck the debris shields and the energy spectrum of the backscattered ions was measured. A peak consistent with a thin layer of target material on the debris shields was observed in the central portion of the debris shields. The ion beam was focused so that it struck different positions on the debris shield, and the intensity of the peak was measured as a function of position. RBS allows the concentration and depth of the target material in the debris shield to be measured, which can be used to infer information about the energy and intensity of the target ions accelerated by the laser in the MTW experiments. |
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JP11.00125: The 30R-Target Chamber Manipulator Christopher J Ventre, Bryan J Diaz, Connor T McDermott, Stephen J Padalino, Charlie G Freeman, Edward Pogozelski The Target Chamber Manipulator (TCM) system allows users to remotely control the angular positions of multiple detectors in the high vacuum 30R end station of the 1.7 MV tandem Pelletron accelerator. Previously, in order to accumulate data from a surface barrier detector at various angular and radial positions, the vacuum chamber was first filled with 1 atmosphere of dry nitrogen, then opened to atmosphere so that the detectors could be repositioned by hand. Evacuating the chamber required several more hours. The entire process took approximately 6 hours to complete, this added substantial time to those experiments requiring frequent repositioning of the detectors. To mitigate this problem and reduce vacuum failure risks from excessive cycling, a TCM system was designed and built at SUNY Geneseo. The system uses LabVIEW to control stepper motors to move the detectors in the chamber. Prior to the summer of 2022, the TCM software contained a flaw that made detection of the stepper motor position and encoder output inconsistent. During the summer of 2022, improvements to COM port detection and assignment were made to ensure the LabVIEW program would recognize all TCM hardware without user troubleshooting. Additionally, many software bugs were eliminated by removing the braking subsystem entirely and replacing it with automated stepper motor adjustments. Manipulator component prototyping was improved by utilizing resin printing. Resin printing is a form of additive 3D printing that utilizes a photopolymer resin with minimal outgassing properties. The ability to prototype detector mounts and various other vacuum safe components in a relatively short time is valuable. Funded in part by the US Department of Energy through the Laboratory of Laser Energetics. |
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JP11.00126: Atmospheric Low-Temperature Plasma Treatment of Wisconsin Fast Plants Under Hydroponic Temperature Variation Claire L Pedersen, Jose L Lopez, Daniel E Guerrero In recent years, usable agricultural land has decreased and the prevalence of infectious pathogens resulting from climate change has grown. Low temperature plasmas have previously expressed the ability to increase the growth and yield of treated plants. With this, comes the question of whether this phenomenon extends to being able to heal plants when exposed to stressors. If the ability to revive these plants rings true, it is assumed that the yield and heartiness level will remain significant. A series of tests comparing plasma treated to non-plasma-treated Wisconsin Fast Plants while simultaneously encountering various aquatic temperature stressors are run. Room temperature (25°C), cold (15°C), and hot (35°C) water are used. These values were determined based on the ideal water temperatures for Wisconsin Fast Plants. An initial test using room temperature water was run as a baseline. Plants in the plasma group were treated 30 seconds each, three times per week, using an atmospheric pressure plasma jet (APPJ) utilized in previous studies. Similar results between the control and plasma-treated plants were exhibited. It is expected that the plasma-treated plants will exhibit a larger difference in height, flower number, and leaf number than that of the non-treated crops |
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JP11.00127: Inductively Coupled Ion Source Studies for Application to the DIII-D Neutral Beam System. Joel Hurtado, Daniel A Klasing, Brendan J Crowley, J T Scoville Neutral beam injection (NBI) is a tool primarily used for heating and current drive in a tokamak. NBI requires a source of ions that are then accelerated and neutralized to produce the beam that is injected into the plasma. At DIII-D, the current plasma source utilized is the Common Long Pulse Source. This is an arc discharge plasma source that, when operated at higher powers and ion densities, is prone to failures of plate-to-plate insulating gaskets and tungsten filaments. As part of the DIII-D five year plan, available neutral beam power will be increased, but reliability must also remain high. For this reason, the prospect of an inductively coupled plasma source is being investigated using a small tabletop sized device. This new device operates with 1 kilowatt of injected power. Axial ion density and electron temperature measurements are taken as well as radial measurements at key locations. Engineering considerations such as antenna coupling and thermal properties of chosen materials are also investigated to inform future engineering models for a possible future full-sized ion source. |
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JP11.00128: Interpretation of far-SOL collector probes during the SAS-VW campaign on DIII-D Aaron A Huang, Shawn A Zamperini Tungsten (W) deposition patterns along collector probes inserted during the SAS-VW campaign on the DIII-D tokamak plan to be interpreted with the 3D Monte Carlo code 3DLIM. W is eroded from the closed SAS-VW divertor as a trace impurity, from which it transports throughout the SOL until deposition on a collector probe or wall surface. Interpretively modelling the deposition patterns in 3DLIM enables estimating unknown parameters such as the radial transport speed of the W ions and the density of W in the SOL. By comparing the relative magnitude of W deposition on each side of the probe, the primary direction of W ions feeding into the far-SOL is measured, and results will be compared against previous results in which near-SOL W accumulation was (indirectly) measured during the 2016 DIII-D W Metal Rings Campaign (MRC). The absolute magnitude of W deposition along the probes will be compared to previous results from MRC, demonstrating how the leakage of W from a closed divertor differs from that of an open divertor such as that used in MRC. The expected results aim to show how modelling experimentally measured deposition patterns with 3DLIM enables rich interpretation of impurity transport in a region with very limited measurements. |
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JP11.00129: Effect of changing coil complexity and magnetic boundary accuracy weights on stellarator coil optimization Alexander V Wiedman, Matt Landreman, Stefan Buller
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JP11.00130: Resolving extended space and time correlations in molecular dynamics simulations of strongly magnetized plasmas Julia L Marshall, Louis Jose, Scott D Baalrud Strongly magnetized plasmas are characterized by having a gyrofrequency larger than the plasma frequency. In this regime, the motion of charged particles is constrained to small cylinders with a width characterized by the gyroradius and a length characterized by the collision mean free path. Recent molecular dynamics simulations showed that this channeling effect leads to increased temporal and spatial correlations associated with Coulomb collisions [1]. These simulations used cubic domains, which significantly limited the range of magnetization strength that they could explore because it required a large number of particles to resolve the long-range correlations. Here, we show that an elongated domain in the direction of the magnetic field can capture the effects with significantly fewer particles than a cubic domain. We define a unit cubic domain by the size needed to capture weakly magnetized plasmas, then elongate the domain by adding additional cubes in the direction parallel to the magnetic field. A proof of principle is demonstrated by computing the self-diffusion tensor of the strongly magnetized one-component plasma using the velocity autocorrelation function. [1] Vidal, Baalrud, Phys. Plasmas 28, 042103 (2021). |
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JP11.00131: A Comparison of VMEC and SPEC Equilibria for Tokamak and Stellarator Configurations Priya Keller, Michael Couso, Andrew S Ware, Stuart R Hudson An extensive comparison of the equilibria from VMEC [S. P. Hirshman and O. Betancourt, J. Comput. Phys. 96, 99 (1991)], an Ideal MHD equilibrium code which assumes continuous nested flux surfaces, and SPEC [S. R. Hudson, et al., Phys. Plasmas 19, 112502 (2012)], an Ideal MHD equilibrium code which assumes a multi-region relaxation model (the pressure is flat except at a finite number of flux surfaces), is undertaken. Equilibria with the same boundary, volume-average beta, and rotational transform on the finite number of surfaces assumed in SPEC are developed for comparison. The comparison will include the shapes of the interior surfaces, profiles of pressure, rotational transform, and current density. The comparisons will include axisymmetric configurations and fully 3-D configurations. The axisymmetric configurations include a tokamak with an elliptical cross-section and an ITER configuration. The stellarator configurations include simpler ones such as a CTH configuration and we are attempting to develop a comparison for a strongly shaped configuration such as W7-X. The results of the comparisons will be presented. |
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JP11.00132: Development and Calibration of a Thomson Scattering Diagnostic for Analyzing Plasmas Generated by the High Amperage Driver for Extreme States (HADES) Aidan Bachmann, Pierre-Alexandre Gourdain Probing dense plasmas to determine their properties is a difficult challenge in HEDP. Direct measurements of local quantities such as electron-ion drift velocity, bulk velocity, electron density, and plasma temperature are not possible. A Thomson scattering diagnostic, which involves scattering low energy photons (Ephoton = ħ?? ≪ mec2) off of electrons in a plasma and capturing the spectrum of scattered light at a specific angle, allows for measuring these local quantities. The calibration of a Thomson scattering diagnostic is multi-faceted, involving not only the alignment of optics to send light through a target, but also the fine positioning of collection optics and the development of software to process Thomson spectra. We will discuss the steps being taken in order to develop a functioning Thomson scattering diagnostic for use on the HADES pulsed power driver. |
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JP11.00133: Deep-learning-based Molecular-Dynamics Simulations of Iron in Planetary Core Conditions Lianming Hu, Shuai Zhang, Maitrayee Ghosh, Suxing Hu Developments of machine-learning techniques in recent years have enabled large-scale simulations of a variety of systems with high accuracy, while applications of such approaches to the study of materials at extreme conditions are relatively few. In this presentation, we report on the construction and application of deep-learning potentials for molecular-dynamics (MD) simulations of iron at planetary-core conditions (multi-megabar in pressures and several thousand Kelvin in temperature). The simulations show cooperative diffusion along <111> directions of body-centered cubic iron, a special state of iron near melting that has many geophysical implications, as clarified lately through ab initio MD simulations.[1] Furthermore, we will discuss findings about melting and solidification of iron through equilibrium and nonequilibrium simulations, which shed light on the high-pressure phase diagram of iron and its dependence on the compression technique. Both are important but open questions in high-energy-density sciences. [1] M. Ghosh, et al., “Cooperative Diffusion in Body-Centered-Cubic Iron at Earth and Super-Earth’s Inner Core Conditions,” submitted to Nature Communications.
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Author not Attending |
JP11.00134: The EPaX experiment at the University of San Diego (USD), designed to study internal sheaths and ultimately the Bohm Criterion in electronegative, Iodine plasma Lena Belvin, Aaliyah Marshall, Gregory Severn There remain open questions regarding the physics of sheath formation in electronegative plasma systems, despite their multifaceted use in plasma processing over the past half-century. While the model of Braithewaite and Allen [J. Phys. D: Appl. Phys. 21 1733 (1988)] is generally assumed to be the case, direct experimental benchmark experiments are still lacking. Further, a focused set of benchmarking experiments directly measuring potential profiles in the neighborhood of sheaths near conducting boundaries, for a variety of electronegativities, is also still lacking. A thermionic emission, DC-discharge device at the University of San Diego (USD), a principally undergraduate institution, called the Electronegative PlAsma Sheath EXperiment, or EPaX, is nearing completion, designed for discharges using corrosive gas feed stocks such as molecular iodine. The plan is to commission the device in Argon, then Argon-Iodine discharges with a view to using the Argon fraction as an experimental knob for electronegativity. The first discharges are now planned for Summer of 2022. Overall design of experiments, progress, and results will be presented. |
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JP11.00135: Does sheath expansion around Langmuir probes, used near material boundaries, depend only on the probe bias relative to the plasma potential? Adrian Woodley, Mohammedali Mohamed, Gregory Severn Langmuir probes (LPs) measure an unphysically positive plasma potential in the presheath of low temperature plasma, near conducting boundaries at which ion rich sheaths form [Li et al., Plasma Sources Sci. Technol. 29 (2020) 025015]. The difference between plasma potential profiles measured by LPs and emissive probes (EPs), in the presheath, is consistent with the effects of ion flow, the signature of which is known to appear in the electron branch of the current-voltage characteristic of LPS. We present experimental evidence that the electron density is also overestimated by standard analysis in the presheath, and that the two anomalies are interrelated, having to do with ion flow near the boundary where an ion rich sheath forms. We exhibit evidence to support this claim for experiments performed in weakly collisional (λmean-free-path >>λD), low pressure (Pneutral ≤ 1 mTorr), low temperature (kTe of order 1 eV), single ion species plasma, where the feedstock gas is Ar or He or Xe or Kr. We also attempt to perform Laser-induced Fluorescence measurements to locate the sheath edge to aid in demarcating the presheath region in Kr plasma specifically. |
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JP11.00136: Characterizing and developing circuit models for improved control of inductive helicity injectors on HIT-SIU Zachary L Daniel, Kyle D Morgan, Christopher J Hansen, Aaron C Hossack
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JP11.00137: Modeling magnetic fields for TREX drive cylinder using COMSOL Isaac Barnhill, Paul Gradney, Jan Egedal, Cary B Forest, Samuel Greess, Alexander Millet-Ayala, Joseph R Olson, Cameron Kuchta, John P Wallace, Mike Clark The Terrestrial Reconnection EXperiment (TREX) at Wisconsin Plasma Physics Laboratory (WiPPL) [1] aims to explore the kinetic collisionless regime of magnetic reconnection. The drive cylinder geometry induces an anisotropic electron distribution in the reconnection region. Lundquist numbers up to S = 105 are accessed by reducing the overall inductance of the power supply and applying a rapidly increasing voltage to the drive coils such that the experimental runtime (<10 μs) is comparable to the collisional time of the plasma (1 μs). Compared to TREX’s previous 4-coil configuration [2], we estimate that the drive cylinder reconnection current layer will be up to a factor of 2 longer, achieving a maximum system size of L/di ≈ 20, and we expect to increase the reconnection electric field tenfold. Based on a multi-coil model to approximate the boundary conditions of the cylinder, we expect that the field interior to the cylinder will be straighter throughout the volume. The drive cylinder will be modeled using COMSOL to confirm the validity of this approximation. COMSOL uses a finite-element method to more realistically model the geometry and numerically solve Maxwell’s equations with the appropriate boundary conditions and time dependence of the coil current. |
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JP11.00138: Development and Implementation of a Four-Tip 3D Mach Probe Arranged in a Tetrahedral Geometry on MST device* Allyson M Sellner, Abdulgader F Almagri, Karsten J McCollam, Michael Reyfman, John S Sarff, Cary B Forest, Jens Von Der Linden, Jason Sears, Setthivoine You, Haruhiko Himura To examine the momentum redistribution processes and study general helicities during plasma relaxation in the RFP, a new prototype 3D Mach probe has been designed and tested to measure 3D plasma flow. The probe consists of four biased molybdenum electrodes to measure the 3D ion velocity. The geometric addition of the logarithms of ion saturation currents allows 3D vectors to be calculated from the tetrahedral geometry. Additionally, the probe has three orthogonal magnetic coils to measure the equilibrium and fluctuating magnetic field. Plasma perturbation should be minimized, so the conducting shell of MST and return electrodes at various distances from the tips are all being tested to determine the optimum location for the return current. A multi-channel power supply is used to bias the Mach tip electrodes and measure the collected current of each tip and the return electrode with voltage dividers. All five currents are connected to a 100 kHz isolation amplifier. The magnetic signals are integrated with a 250 kHz bandwidth. All signals are digitized at 1 MHz. Preliminary results, calibrations, drawings and photos will be presented. |
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JP11.00139: Particle Transport During the L-H transition Using Machine Learning* Javier E Chiriboga, Saskia Mordijck, Kathreen E Thome, Thomas H Osborne, Lothar Schmitz Density rises following the low to high confinement mode transition (L-H transition) differ based on isotopically dependent transport properties. In hydrogen plasmas on DIII-D compared to deuterium, the linear increase in electron density is almost 50% faster for hydrogen during the L-H transition. The confinement mode change of low confinement (L-mode) to high confinement (H-mode) is helpful for fusion in tokamak plasmas as it decreases turbulent transport near the edge resulting in increased electron densities and sharp density and temperature gradients. We present transport differences between hydrogen and deuterium plasmas by comparing transport coefficients obtained through an optimization that matches a convective-diffusive fluid model along with an exponential fueling model to experiment in both time and space. A Machine Learning algorithm trained using the optimization algorithm replicates and predicts transport coefficients. Using the neural network, we analyze how differences in species affect electron transport during the L-H transition. |
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JP11.00140: An Expanded Python Version of KN1D for Modeling the Neutral Densities of SPARC Gwendolyn R Galleher, Griffin Heyde, Nick Holland, Alexander J Creely, Matthew L Reinke, Saskia Mordijck In fusion research, predicting neutral profiles is critical to understand the fueling requirements for a fusion reactor [1]. KN1D [2], developed in the ‘90s, relies on a collisional-radiative model for the 10 most important electron interactions [3], and elastic collisions are included using a BGK model [4] instead of using modern open-source databases of atomic physics reactions [5]. We will first convert KN1D into Python to simplify its use for the wider community and improve compatibility with experimental data as well as predictive modeling. |
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JP11.00141: A Python Version of KN1D for the Training of a Neutral Density Predicting Machine Learning Algorithm Griffin Heyde, Saskia Mordijck, Gwendolyn R Galleher, Nick Holland, Alexander J Creely, Matthew L Reinke In fusion research, predicting neutral profiles is critical to understanding the fueling requirements for a fusion reactor [1]. KN1D [2] uses a collisional-radiative model for the 10 most important electron interactions [3], and elastic collisions are included using a BGK model [4]. We will first convert KN1D into Python to simplify its use for the wider community, improve compatibility with experimental data and predictive modeling, and allow easier coupling to ML and AI algorithms. The Python version is verified by comparing it to the previous IDL version using data from the C-Mod tokamak at MIT. A ML algorithm will then be trained with a synthetic database of input/output files from KN1D. Inputs outside of the training data are then put through both the algorithm and KN1D, with any deviations being amended after comparing outputs. The main advantage of a well-trained machine learning algorithm is that it can significantly reduce the computational requirements of calculating neutral densities compared to KN1D. |
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JP11.00142: Updating KN1D into Python for Improved Modeling of Neutral Profiles Nick Holland, Griffin Heyde, Gwendolyn R Galleher, Saskia Mordijck, Alex J Creely, Matthew L Reinke, Jerry W Hughes In fusion research, predicting neutral profiles is critical to understand the fueling requirements for a fusion reactor [1]. KN1D [2], written in IDL, includes collisional-radiative models for atoms and molecules, and accounts for the 10 most important electron interactions; elastic collisions are included using a BKG model. However, atomic physics cross-sections have remained unchanged since the time of initial coding. We will first convert KN1D into Python to simplify its use for the wider community and improve compatibility with experimental data as well as predictive modeling. |
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JP11.00143: Effect of density gradient and neutral density on drift-wave turbulence in LAPD Leo Murphy, Saskia Mordijck, Troy Carter, Steve Vincena, Thomas Look, Phil Travis Magnetized plasmas with cross-field pressure gradients experience drift-wave turbulence. In magnetic confinement devices like the Large Plasma Device (LAPD), drift-wave turbulence is driven by electron density and temperature gradients, which directly affect cross-field particle and heat transport (Tynan et al. 2009, Carter et al. 2006). In previous experiments on LAPD, drift-wave density fluctuations increased with increasing density gradient, while introducing a small temperature gradient damped density fluctuations and reversed the cross-phase between density and potential fluctuations, altering the direction of particle flux. While changes in neutral pressure shifted parallel flow profiles and potential fluctuations (Perks et al. 2022). Experiments on LAPD were performed with a new LaB6 cathode to access higher electron densities and temperatures. The cathode current and gas puff were altered to study higher density gradients and the impact of gas puffing versus pre-filling on turbulence and parallel flows. The electron temperature was measured using Langmuir probes, electron density and fluctuations using 4-tip probes, and parallel flow using Mach probes. Data analysis is ongoing, but from interferometer data, electron density increased non-linearly with cathode current. |
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JP11.00144: Reversal of Microparticle Motion at the Onset of Polarity Switching in Ground-Based PK-4 Experiments Zachary Howe, Jeremiah D Williams, Lori Scott-McCabe, Edward Thomas, Uwe Konopka, Navy Ferris, Mikhail Pustylnik, Hubertus Thomas The behavior micron-sized particles (dust) in a plasma system are of great interest, both as a model system for studying a wide range of physics and in practical applications. In ground-based experiments, the high mass of the dust leads to sedimentation effects. To reduce sedimentation effects, it is necessary to perform experiments in a microgravity environment, such as in the ISS based experiment facility "Plasma-Kristall-4" ("PK-4"). In the PK-4 facility, particles are injected into a dc glow discharge plasma and flow along an axial electric field. Upon the application of polarity switching (a periodic oscillation of the electric field), a sudden change in the bulk motion and spatial ordering of the dust is observed. This poster will present the results of a study of the thermal state of dust particles within the PK-4 experiment as the frequency of polarity switching is varied. |
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JP11.00145: Design of a Four-Pin Triple Langmuir Probe for the Pi3 Spherical Tokamak at General Fusion Inc. Benjamin Y Brown, Celso Ribeiro, Russ Ivanov, Meet Nandu, Mark Bunce, Kelly Epp, Adrian Wong, Kathryn Leci, Alexander D Mossman, Michel Laberge, General Fusion Team A four-pin triple Langmuir probe has been developed for General Fusion’s spherical tokamak PI3. The probe head is boron nitride with four 0.6 mm diameter, 3mm length, 4mm interspace tungsten wires exposed to the plasma. A DC voltage of 50-100V is applied between two pins while floating potential is measured by the other two. The triple probe method allows the electron temperature and density, and plasma potential to be inferred from the probe. The four-pin configuration additionally allows poloidal E field fluctuations to be inferred, thus the fluctuation-driven radial particle flux. |
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JP11.00146: Surface modification of brass by atmospheric-pressure plasma jet treatment Mauricio A Erazo, Jennifer Aggrey, Eli Fahrenkrug, Adam D Light Surface modification of brass by atmospheric pressure plasma remains relatively unexplored. As an alloy of reactive metals, brass provides an interesting substrate to study plasma-surface interaction. Surface modification of brass was performed using an argon-fueled atmospheric pressure plasma jet at room temperature. We focused on increasing the wettability of the surface by observing changes in the contact angle at the solid-liquid interface over time following the Young-Laplace equation. Contact angle of water droplets on treated brass surfaces decreased significantly when compared to untreated surfaces. The wettability decreased over time, and the contact angles reverted to their original values. By using Raman spectroscopy, we hope to identify the chemical species that produce this temporary and reversible surface modification. We present our experimental setup, analysis techniques, and preliminary results. |
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JP11.00147: Investigating Magnetic Moment Conservation in Time and Spatially Varying Electromagnetic Fields Stephan Jabs, Cole D Stephens, David R Hatch Gyrokinetic models have been extremely useful in simulating plasmas with slowly |
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JP11.00148: Study of the radial requirements for accurate predictions of tokamak profiles and fusion performance Subhash C Kantamneni, Pablo Rodriguez-Fernandez, Nathan T Howard, Jerry W Hughes, Amanda E Hubbard Temperature and electron density profile predictions for tokamak fusion experiments involve simulating profile gradients at a set number of points and integrating to predict kinetic profiles (ne, Te, Ti). Using first-principle simulations to calculate points in this gradient interpolation is very computationally intensive, motivating the use of as few points as possible. 20 years of discharges from Alcator C Mod were used to determine the optimal number of points and locations needed to accurately predict profiles and fusion power. Each discharge was fit with a gaussian process based fitting routine, and the normalized logarithmic gradients were calculated. In the normalized minor radius range of 0.2 to 0.9, for a 3-point gradient interpolation, the best points were at r/a=0.5,0.825,0.9; for a 4-point gradient interpolation, r/a=0.45,0.7,0.85,0.9; and for a 5-point gradient interpolation, r/a=0.35,0.55,0.75,0.875,0.9. With these points, a 3-point interpolation created a mean error of 5% in the fusion power with a 25.5% standard deviation; 4 points had .7% and 10%; while 5 points had .05% and 6.8%. These results suggest that a reduced set of local turbulence simulations for profile prediction in the core of inductive, on-axis heating scenarios can provide sufficiently accurate results. |
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JP11.00149: Ultraviolet LED Triggered Spark Gap Liam P Keeley, Brian L Henning, Adam D Light We present progress towards a novel spark gap switch triggered by light from an LED. Pulsed light at 275 nm is focused on the electrodes to seed breakdown via the photoelectric effect. In order to understand the operation and limitations of the device, we include the photoelectrons as a low energy beam in a streamer breakdown simulation. We plan to integrate a local electron source term into a conventional two-fluid model using the Afivo framework [1]. We expect negative streamers to form at lower voltages than are typically observed due to electric field enhancement from the locality of the source and the non-neutral nature of the beam. We describe our experimental setup and observations, as well as preliminary interpretations of the physics guided by simulation. |
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JP11.00150: Analysis of the rarefaction wave in a screw pinch plasma configuration Abhishek Mhatre, Cameron Kuchta, Jan Egedal
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JP11.00151: Development of force distribution based plasma kinetic theory Colin J Stewart, Scott D Baalrud In contrast to the usual velocity distribution based kinetic theories, a theory based on the force distribution of a particle is developed and tested. The force on a test charge is related to the relative velocity of a collision through the averaging of impact parameters and solid angle. This process provides a coordinate transformation of the velocity distribution to a force distribution. This approach has the benefits of more direct relation to bremsstrahlung radiation and some experimental measurements, such as stopping power measurements in inertial confinement fusion experiments. The theory is evaluated with the Rutherford cross-section as well as cross-sections from models of strongly coupled plasmas and compared to molecular dynamic simulations created by passing a test charge through a one-component background and measuring the force on the particle at each time step. Comparisons with different coupling strengths determined by the ratio of coulombic potential energy to thermal kinetic energy were performed. |
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JP11.00152: Correcting Thomson Scattering Electron Density Measurements Using Alignment Monitors Laura Jian, Fenton Glass Electron density measurements via Thomson scattering rely on an absolute calibration, relating the number of scattered photons to signal levels in spectral detectors. Misalignment between the calibrated positional relationship of the scattering volume in the plasma and the collecting optics may lead to fewer photons collected and thus an increased error in the density measurement. Scattered light collected with a dedicated and specialized optical fiber bundle that spans the volume — monitoring the accuracy of the alignment — is used to estimate the reduction of collected photons in the main collection fiber bundles. The validity and results of correcting the electron density measurements via these alignment monitor data are investigated. |
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