Bulletin of the American Physical Society
75th Annual Gaseous Electronics Conference
Volume 67, Number 9
Monday–Friday, October 3–7, 2022;
Sendai International Center, Sendai, Japan
The session times in this program are intended for Japan Standard Time zone in Tokyo, Japan (GMT+9)
Session FR2: Low Pressure Plasmas |
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Chair: Kazunori Takahashi, Tohoku University Room: Sendai International Center Shirakashi 1 |
Thursday, October 6, 2022 10:00AM - 10:30AM |
FR2.00001: Instabilities and turbulent processes in low-temperature magnetized plasmas Invited Speaker: Kentaro Hara Low-temperature magnetized plasmas play an important role in natural phenomena and engineering applications, such as material processing and spacecraft electric propulsion. One of the key physical processes that are not well understood in low-temperature magnetized plasmas is the electron transport across magnetic fields. It has been observed from past investigations that cross-field electron transport is enhanced compared to classical theory considering collisional transport, cf. drift-diffusion approximation. Recent experimental, theoretical, and computational studies further suggest that multidimensional plasma waves can be excited due to a variety of plasma instabilities, which may lead to collisionless enhancement of the cross-field electron transport. The nonlinear saturation of such instabilities, both kinetic and fluid, can be influenced by the interactions with various other mechanisms, including plasma-wall interactions, collisional transport, plasma inhomogeneity, circuit effects, and facility effects. In this talk, we will review the various plasma instabilities that lead to plasma turbulence within low-temperature magnetized plasmas and discuss the potential mechanisms of electron transport and diffusion across the magnetic field without any collisions. The results obtained from our multidimensional kinetic models show that the cross-field electron transport is affected by the amplitude and wavelength of the plasma waves. Singly particle trajectory simulations suggest that the magnetized electrons may be stochastically heated due to the presence of the multidimensional plasma oscillations. The understanding of such turbulent transport also plays an important role in developing reduced-order fluid models to capture some dynamical and finite non-Maxwellian effects. |
Thursday, October 6, 2022 10:30AM - 10:45AM |
FR2.00002: Initial Characterization of the EEDF of an ECR-based Plasma Cathode Operating on Molecular Gases Anil Bansal, John E Foster, Michael S McDonald Electron cyclotron resonance (ECR) plasma cathodes utilize RHCP wave heating in a magnetic field to ionize a neutral gas. The extraction of electrons from this device is dependent on the ratio of charged-particle collecting areas; therefore, the source region (where the ionizations occur) is biased negatively to collect ions, while the electrons are collected at a downstream anode. This work seeks to characterize and evaluate the performance of ECR plasma cathodes on molecular gasses, for purposes such as in-situ utilization. Previous experimental testing with this configuration has identified the presence of an electron beam escaping downstream of the anode, representing a collection loss in the device. The goal of this work is therefore to first characterize the energy distribution of this escaping electron beam, and then to identify ways to control this EEDF to reduce beam loss in the device, thereby increasing extracted current and device efficiency. |
Thursday, October 6, 2022 10:45AM - 11:00AM |
FR2.00003: Analyses of enhancement of energy deposition to electrons by partial resonance in an inductively coupled plasma under confronting divergent magnetic fields Ryota Okazaki, Hirotake Sugawara We performed Monte Carlo simulations of a low-pressure inductively coupled plasma under confronting divergent magnetic fields (CDMFs) and observed the electron energy gain (EEG) under different configurations of electric field distributions and magnetic field strengths in order to understand the partial resonance phenomenon and to seek for desirable reactor design for utilization of the partial resonance. The separatrix of the CDMFs has a function to confine plasma, with which high plasma density and low-damage material processing are expected. However, strong magnetic fields suppress the EEG. Then we focus on the EEG by partial resonance observed in a resonant magnetic field region where the magnetic field strength is close to a specific value BECR = 2π(m/e) frf (e and m are the electronic charge and mass, and frf is rf frequency; BECR = 0.4844 mT at frf = 13.56 MHz) associated with the electron cyclotron resonance. The EEG in the resonant region tends to be higher than in its surrounding region, and this tendency is unchanged even in case the resonant region is far from the rf antenna and even under stronger magnetic fields. |
Thursday, October 6, 2022 11:00AM - 11:15AM |
FR2.00004: Diagnosing hydrogen plasma in a high power helicon device Campbell Strachan Neutral Beam Injector systems (NBIs) will provide beam energies up to 1 MeV as part of the heating systems required for future fusion reactors. Positive ion neutralisation efficiency becomes prohibitively low above 100 keV whereas negative ions are capable of maintaining nearly 60% efficiency up to 1 MeV. RF Inductively Coupled Plasmas (ICPs) with powers up to 100 KW are currently used to generate high atomic and positive ion flux onto ceasiated surfaces to achieve sufficient negative ion densities. Helicon Coupled Plasmas (HCPs) can generate comparable plasma densities at lower applied power, however, few studies on HCPs have been conducted at low pressures less than 10 mTorr and high powers greater than a few kW for application as NBI sources. In this study we characterise a high-power HCP operating with hydrogen up to 20 kW between 2.5 and 10 mTorr in the MAGPIE device at the Australian National University. This includes power coupling measurements, electron densities and temperatures, atomic and molecular temperatures in the source and diverging magnetic field regions. Compared with the inductive mode, higher plasma densities and dissociation fractions are observed when operating in the helicon mode. Experimental measurements are compared with results from a 0-dimensional model. |
Thursday, October 6, 2022 11:15AM - 11:30AM |
FR2.00005: Surrogate models of capacitively-coupled plasmas by machine learning Kazumasa Ikuse, Masakazu Ichikawa, Kuan-Lin Chen, Jong-Shinn Wu, Fatima Jenina T Arellano, Zoltan Donko, Satoshi Hamaguchi Numerical simulations of radio-frequency (RF) driven capacitively-coupled plasmas (CCP) were performed under various conditions and the obtained phase-averaged profiles of their physical quantities such as the electron density and electrostatic potential were used to construct surrogate models of the plasma discharge. While the first-principles-based plasma simulation requires some time to predict the steady-state plasma profiles correctly under the given discharge conditions, the surrogate model can predict such profiles instantaneously because it interpolates the stored data.[1] Such surrogate models, if constructed for realistic plasmas with complex gas chemistry, could be used for the real-time control of plasma processing. In this study, we used one-dimensional fluid-model (FM) and particle-in-cell/Monte Carlo collision (PIC/MCC) simulations of argon CCP to obtain profile data. The neutral-network-based model that we constructed was found to be the best among our other models based on different regression techniques. Because PIC/MCC simulations are more time-consuming than FM simulations, we applied a transfer learning with extensive FM simulation data and a relatively small amount of PIC/MCC simulation data. |
Thursday, October 6, 2022 11:30AM - 11:45AM |
FR2.00006: Study of the collisional effects and increasing perpendicular magnetic field on the expansion of a laser produced plasma. Zachary K White, Gabe Xu Laser produced plasmas have been used to study shock, astrophysical, and fusion phenomena. In our study, we have utilized the highly uniform superconducting magnets of the Magnetic Dusty Plasma Experiment (MDPX) to better understand the cross-field motion of a moderately dense, 1018 #/cm3, across a broad range of magnetic field strengths. MDPX allowed us to measure the behavior of plasmas generated by a Nd:YAG laser focused onto a cylindrical carbon fiber target in magnetic fields up to 3.25 Tesla. The background pressures were also varied from 100 mTorr to 300 mTorr to observe the effects of collisionality on the plasma structure. We were able to capture the structure of the laser produced plasma using an intensified charge couple device (ICCD) with time resolution of 3 ns. The images obtained were taken perpendicular and parallel to the plasma expansion and the magnetic field. We measured the plasma expansion out to a time of 1000 ns and found that with increasing field the critical radius of the plasma expansion decreased as the magnetic field got stronger. We also observed a bifurcation in the plasma expansion as the plasma expanded over time. |
Thursday, October 6, 2022 11:45AM - 12:00PM |
FR2.00007: Novel Transport Properties of Strongly Magnetized Plasmas Scott D Baalrud, Louis Jose, Trevor Lafleur Plasmas that are so strongly magnetized that the electron gyrofrequency exceeds the electron plasma frequency exhibit novel transport properties. This talk summarizes examples obtained from a combination of molecular dynamics simulations, linear response kinetic theory, and generalized Boltzmann theory calculations. First, we consider an ion slowing as it passes through strongly magnetized electrons. A common expectation is that the drag force is antiparallel to the velocity of the ion, causing it to slow. A novel behavior observed to be caused by strong magnetization of the electrons is that the drag force has components perpendicular to the velocity of the ion. These can cause non-intuitive behaviors of the ion trajectory, such as an increase in the ion gyroradius due to a deflection of the ion into the direction perpendicular to the magnetic field by the electrons. Another observation is that strong magnetization causes a Barkas effect, where the drag force is strongly dependent on the sign of the interacting charges: an effect that is not present in standard Coulomb collision theory. These novel single particle effects are shown to translate into large changes in macroscopic transport processes, including a large change to the electrical resistivity tensor. |
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