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 TO07: Fundamental Plasmas: Elementary Plasma Processes and DiagnosticsLive Streamed
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Chair: Earl Scime, WVU Room: 401 ABC |
Thursday, October 20, 2022 9:30AM - 9:42AM |
TO07.00001: Thermal Waves in an Inhomogeneous Magnetized Plasma Pressure Filament Scott Karbashewski, Richard D Sydora, Bart G Van Compernolle, Matthew J Poulos Results are presented from basic heat transport experiments using driven thermal waves in a magnetized plasma pressure filament. Using a small cathode source, low energy electrons are injected along the magnetic field into the afterglow of a pre-existing plasma forming a hot electron filament embedded in a colder plasma. A series of low amplitude, sinusoidal perturbations are added to the cathode discharge bias that creates an oscillating heat source capable of driving large amplitude electron temperature oscillations [1]. Langmuir probes are used to measure the amplitude and phase of the thermal wave field over a wide range of driver frequencies. The results are used to verify the excitation of thermal waves, confirm the presence of thermal resonances, and demonstrate the diagnostic potential of thermal waves through measurement of the parallel thermal diffusivity [2]. |
Thursday, October 20, 2022 9:42AM - 9:54AM |
TO07.00002: High-sensitivity plasma density characterization by cross-polarized temporal interferometry Zan Nie, Noa Nambu, Kenneth A Marsh, Eric C Welch, Daniel Matteo, Chaojie Zhang, Yipeng Wu, Serguei Patchkovskii, Felipe Morales, Olga Smirnova, Chandrashekhar Joshi Absolute density measurements of low-ionization-degree or low-density plasmas ionized by lasers are very important for understanding strong-field physics, atmospheric propagation of intense laser pulses, Lidar etc. A cross-polarized common-path temporal interferometer using balanced detection was developed for measuring plasma density with a sensitivity of ~0.6 mrad, equivalent to a plasma density-length product of if using an 800 nm probe laser. Using this interferometer, we were able to measure plasma density over 5 orders of magnitude, which allowed us to verify different photoionization models in tunneling and multiphoton regimes. We have investigated strong-field ionization yield versus intensity for various noble gases (Ar, Kr, and Xe) at different wavelengths (267-800 nm) with both linear and circular polarizations. The experimental results were compared to ADK and PPT models as well as TDSE simulations. Since our method is sensitive to the refractive index, we can also measure the population of Rydberg states, which have similar susceptibility as free electrons. In some special cases, our experimental results showed a significant population of Rydberg states excited by multi-photon resonances, which was confirmed by TDSE simulations. |
Thursday, October 20, 2022 9:54AM - 10:06AM |
TO07.00003: Using laser induced plasma to characterize performance of HTGR advanced alloys Tyler E Ray New advanced alloys for fission and potential fusion reactor designs are gaining traction while systems in place to analyze the inevitable material degradation via irradiation, high temperature, and corrosive environments have not changed. At the center for materials under extreme environments (CMUXE), Purdue University, we are developing methods using laser induced plasmas to further analyze Alloy 617, recommended for new HTGR cooling loops for its superior high temperature mechanical strengths. Recent studies have shown that impurity gases in the helium loop can cause significant oxide formation on the surface affecting various mechanical properties, including hardness during the high temperature operation. At CMUXE, methods to perform mechanical testing and diagnose oxide layer formation are currently being conducted using laser induced breakdown spectroscopy (LIBS). A variety of extreme environments are being tested in our facility to simulate different cooling loop environments in HTGRs with possible fusion reactor applications. Current work investigates spectral variations seen during high temperature LIBS testing to analyze material composition, spatial distribution, and mechanical properties during reactor operations with high accuracy. The goal is to further investigate LIBS at high temperatures to better understand its viability for in-situ measurements in nuclear reactor environments. |
Thursday, October 20, 2022 10:06AM - 10:18AM |
TO07.00004: Remotely Discerning Radioactive Source Type via Laser-Driven Electron Avalanche in Air Anthony Zingale, Stefan K Waczynski, Robert M Schwartz, Jason Sears, Rollin E Lakis, Howard M Milchberg Detection of radioactive material from standoff distances outside the attenuation range of its decay products is of great interest in areas such as nuclear security and disaster response. Development of a new technique based on mid-infrared (λ = 3.9 μm) laser driven electron avalanche has recently been demonstrated (R. M. Schwartz et al., Sci. Adv. 5, eaav6804 (2019), D. Woodbury et al., Optica 6, 811-820 (2019)). In the work presented here, we extend this technique by comparing the breakdown plasmas generated near two different radioactive sources, Fe55 and Po210, emitting 6 keV γ-rays and 5.3 MeV α-particles, respectively. We find that the breakdown sites in air irradiated by Fe55 are larger on average and grow faster than those in air irradiated by Po210. This is detectable at range through a Doppler shift in the backscattered spectrum. Ionization track simulations support this, showing ionization clusters with locally high seed density that lead to faster avalanche growth in the case of Fe55, and a more uniform ionization distribution in the case of Po210. Our comparison of two different source types, shows that the avalanche plasma detection method is sensitive to the specific local ionization distribution, possibly allowing for source differentiation at long range. |
Thursday, October 20, 2022 10:18AM - 10:30AM |
TO07.00005: Understanding the competitive behavior of recombination processes and their effect on ionization balance and radiative loss rate Prashant Sharma, Christopher J Fontes, Mark C Zammit, James Colgan, Hyun-Kyung Chung, Xianzhu Tang The study of ionization balance is critical to assess the plasma dynamics in a range of plasmas, such as low density (e.g., astrophysical plasma), intermediate density (e.g., magnetic fusion plasma), and high density (e.g., Z-pinch plasma). Importantly, the ionization balance is governed by different mutually competing atomic processes, such as electron-impact ionization, autoionization, electron excitation, deexcitation, recombination, etc. In the present work, we have performed a detailed study to understand the competitive behavior of recombination processes, i.e., charge-exchange, radiative recombination, three-body recombination, and electron capture, and their effect on the ionization balance. We have employed a steady-state collisional radiative model to calculate the level population densities in nitrogen-hydrogen and neon-hydrogen mixture plasmas, where the requisite rate coefficients of several atomic processes are computed using the Maxwellian distribution. The calculated level populations are then used to determine the charge-state distribution and average charge state of the plasma species. Further, we have also studied the variation of radiative loss rate with respect to temperature, and the effect of including the different recombination processes in order to ascertain their crucial role in plasma cooling. The results presented at the meeting will be accompanied with detailed explainations of the important physical phenomena. |
Thursday, October 20, 2022 10:30AM - 10:42AM |
TO07.00006: Molecular dynamic simulations to assess the non-Maxwellian behavior of inverse-bremsstrahlung heating in weakly coupled plasmas Olivier P Poujade, Ronan Devriendt Classical molecular-dynamics simulations (CMDS) with LAMMPS have been conducted on two components weakly coupled plasmas to investigate non-Maxwellian inverse bremsstrahlung (IB) absorption for moderate ionizations. After a brief description of our simulations restricted to plasmas with maxwellian electron velocity distribution (EVD) at Z = 1, we will present the results of simulations dedicated to the study of non-Maxwellian IB absorption at Z = 10. Deformation of EVDs in Langdon’s conditions is observed for the first time in CMDS. Different EVDs are observed depending upon intensity and initial plasma state, including anisotropic and isotropic supergaussians (predicted by Langdon). The relation between the order of the supergaussian and the laser intensity obtained by CMDS is qualitatively similar but quantitatively different from the one inferred from Fokker-Planck simulations. We have been able to produce a similar relation for the anisotropic orders (parallel to the direction of polarization and perpendicular to it) and found that the parallel order could exceed 5 (limit predicted by Langdon) whereas the perpendicular order remains below that limit. We will finally introduce a heating rate model to tentatively take into account these non-maxwellian effects. |
Thursday, October 20, 2022 10:42AM - 10:54AM |
TO07.00007: The effect of humidity on streamer propagation in long air gaps Andrey Starikovskiy, Eduard Bazelyan, Nickolay Aleksandrov A 2D numerical simulation of the positive streamer properties was performed in 9-12 cm plane-to-plane air gaps for various pressures and water vapor contents. It was shown that an increase in air humidity leads to hampering the streamer development and to increasing the average critical electric field required for bridging the discharge gap. The effect of humidity was most profound at atmospheric pressure and decreased with decreasing pressure. The influence of water content on the streamer properties was explained by a decrease in the streamer channel conductivity due to dissociative recombination of electrons with positive hydrated ions and enhanced three-body electron attachment to O2 molecules. The calculated critical electric field in humid air gaps was compared with available experimental data. An increase in air humidity leads to an increase both in the rate of electron-ion recombination and in the rate of electron attachment. In humid air, the more efficient plasma decay in the streamer channel leads to a decrease in the plasma conductivity and to an increase in the voltage drop along the channel. Streamer head potential and the ionization rate in this region decrease. Consequently, the higher is air humidity, the slower is the streamer discharge development. |
Thursday, October 20, 2022 10:54AM - 11:06AM |
TO07.00008: Kinetic Simulation of Narrow Gap Discharge Sung Hyun Son, Yeong Hwan Choi, Geunwoo Go, Haneul Lee, Hyo-Chang Lee, Alexander Khrabrov, Igor D Kaganovich, June Young Kim There have been numerous studies attempting to understand the mechanism of the discharge breakdown in a narrow gap [1] while the understanding of the phenomena has been limited due to overlooking the complex environment of plasma generation (e.g., detailed chamber structures and gradients of plasma parameters). To precisely understand the narrow gap breakdown, multi-dimensional kinetic simulations have been performed. In this collaborative study, we present the effect of sophisticated variables such as background plasma density, discharge geometry, and external magnetic field on the narrow gap breakdown. Specifically, a significant decrease in the gap breakdown voltage in the presence of background plasma has been reported. The role of background plasma on the undervoltage breakdown is investigated through PIC-MCC simulations using the EDIPIC-2D code [2]. The detailed mechanism of the narrow gap breakdown in these complex conditions and solutions to prevent unexpected discharge will be discussed. |
Thursday, October 20, 2022 11:06AM - 11:18AM |
TO07.00009: Barkas Effect in Strongly Magnetized Plasmas Louis Jose, David J Bernstein, Scott D Baalrud Strongly magnetized plasmas characterized by the gyrofrequency exceeding the plasma frequency exhibit novel transport properties. For example, recent work showed that the friction force on a test charge moving through a strongly magnetized plasma includes components perpendicular to the velocity of the test charge in addition to the normal stopping power component. These works focused on the case that the sign of the test charge is the same as that of the strongly magnetized plasma that it interacts with. Here, we extend the calculation to the case of unlike sign of charges, such as an ion interacting with strongly magnetized electrons. It is found that strong magnetization causes a large Barkas effect, whereby the friction force changes dramatically depending on the sign of the test charge. Good agreement between molecular dynamics simulations and predictions of a generalized Boltzmann kinetic theory are obtained. The combination of the strong magnetization and Barkas effect is found to decrease the parallel electrical resistivity and increase the perpendicular electrical resistivity significantly. |
Thursday, October 20, 2022 11:18AM - 11:30AM |
TO07.00010: Neutrals and Electromagnetic drift-Rossby-Alfvén turbulence: Drag, Entrainment, and Ambipolar Diffusion Chang-Chun Chen, Patrick H Diamond, Mikhail A Malkov, Steven Tobias Interest in the effect of neutrals on drift-Rossby wave turbulence at the plasma boundary is increasing as a consequence of the relevance in high-density regimes, detachment, etc. It has been known that neutral friction damps zonal flows, increases drift wave fluctuations, in the vein of predator-prey trade-offs. More interestingly, edge zonal flow actually entrains neutrals, by ‘shaving off’ the neutrals layers, via momentum conserving coupling. We analyze the coupled system of heat-flux drift wave turbulence, zonal flows, and a neutral population to understand the mechanism of Drift-Rossby-Alfvén turbulence (DRAT). |
Thursday, October 20, 2022 11:30AM - 11:42AM |
TO07.00011: Plasma oscillations in an expanding magnetized ultracold neutral plasma Scott D Bergeson, Chanhyun Pak A recent publication demonstrated radial magnetic confinement in an ultracold neutral plasma [1]. In that work, the initially Gaussian transverse density distribution remained self-similarly Gaussian throughout the plasma confinement time, contrary to known models. We have dramatically improved our ability to measure transverse-expanion ion dynamics in magnetized strongly-coupled neutral plasmas. We show that the hydrodynamic velocity gradient shows oscillations that depend on magnetic field. We also discuss the ion temperature in the parallel and transverse directions. |
Thursday, October 20, 2022 11:42AM - 11:54AM |
TO07.00012: An Analytic Electron-Impact Ionization Anisotropic Scattering Model for Monte Carlo Plasma Modeling James Colgan, Mark C Zammit, Ryan M Park, Christopher J Fontes, Brett Scheiner, Eddy M Timmermans, Xianzhu Tang, Nathan Garland Modeling non-equilibrium plasmas with Monte Carlo collision codes or Boltzmann equation solver codes requires input of collision cross sections and or scattering models. However, scattering models utilized for the ionization anisotropic scattering process have generally not been validated against theory or measurements. Recently we have developed an analytic model for calculating the electron-impact ionization anisotropic angular scattering distribution functions, which can be readily implemented in Monte Carlo simulation codes. Here we present our approach and compare the model to generally utilized scattering models and accurate scattering calculations. |
Thursday, October 20, 2022 11:54AM - 12:06PM |
TO07.00013: Is the Landau damping plays a crucial role in high density and low magnetic field helicon plasma Wenqiu Li, Gang Wang By employing warm plasma model and considering the cyclotron harmonic effect in the dielectric tensor elements, the power deposition properties of the azimuthally symmetric mode of the helicon and Trivelpiece-Gould (TG) waves due to collisional and kinetic damping in high density (~1×1013 cm-3), low magnetic field (~30-50 G) and low to moderate neutral gas pressure (~ 0.5-10 mTorr) helicon plasma are investigated. Theoretical calculations indicate that the magnetic field imposed significant influence on the mode coupling surface properties between the helicon and TG waves; in typical helicon plasma electron temperature range, Te ∈(3, 5) eV, there exist the critical neutral gas pressure, below or above which, different waves due to different damping mechanism play dominant role in the power deposition, meanwhile, in low neutral gas pressure (~0.5 mTorr) circumstances, TG wave due to Landau damping dominates the power deposition and this dominance gradually becomes intensified as the magnetic field increases. |
Thursday, October 20, 2022 12:06PM - 12:18PM |
TO07.00014: Simulation Benchmark of the XPDP1 PIC-MCC Code for Capacitively Coupled Plasma Helium Discharges Guoning Wang, Kaviya Aranganadin, Hua-Yi Hsu, John P Verboncoeur, Ming-Chieh Lin The particle-in-cell Monte Carlo collision (PIC-MCC) code, XPDP1, originally designed by Plasma Theory and Simulation Group (PTSG) at UC Berkeley now at Michigan State University, is an extensively used bounded electrostatic code for modeling one-dimensional (1-D) plasma devices in both academia and industry. In-depth benchmarks of five 1-D PIC-MCC codes for low-pressure capacitively coupled plasma (CCP) discharges were performed by Turner et al. The XPDP1 was left out, nevertheless. In this study, we use the same four cases of CCP discharges in helium to benchmark the simulation performance of the XPDP1 code. We describe the analysis of the differences in a helium CCP discharge between using the imported LXCat data of helium cross sections and the functional cross sections originally used in the XPDP1 code, as the cross section data play a crucial role in describing charge and neutral collisions in a plasma discharge. Along with computing speeds and the amount of time needed to reach steady states, the plasma densities and distributions resulting from various cross sections are contrasted with published PIC-MCC results as well as predictions made by moment models that were implemented in COMSOL Multiphysics. According to the results, the PTSG code users may require an update in order to use the LXCat cross section data for their plasma discharge studies. |
Thursday, October 20, 2022 12:18PM - 12:30PM |
TO07.00015: Steady-state Velocity Distribution of Neutral Atoms with Energy Dissipation Keisuke Fujii Collisional thermalization of a particle ensemble under energy dissipation can be seen in a variety of systems, such as neutral particles in plasmas and granular particle systems. Despite its universal existence, analytical descriptions of the steady-state distribution have been missing. Here, we show that the steady-state energy distribution of a wide class of nonthermal system with energy dissipation can be well approximated by a generalized Mittag-Leffler distribution, which is a stable distribution. This distribution has a power-law tail, similar to Levy's stable distribution, the index of which is related to the relative significance of the energy dissipation rate against the entropy production by elastic collisions. We demonstrate its universality by comparing with a molecular-dynamics simulations as well as spectroscopic observations of the atom velocity distribution in a low-temperature plasma. |
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