Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session NP14: Poster Session: Low Temperature Plasmas (9:30am - 12:30pm)On Demand
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NP14.00001: Plasma Kinetics Modeling of an e-beam Pumped ArF Laser Tzvetelina Petrova, Matthew Wolford, Matthew Myers, George Petrov, John Giuliani, Malcolm McGeoch, Andrew Schmitt, Steve Obenschain The plasma kinetics of an e-beam pumped 193 nm ArF laser is modeled and compared against results from the U.S. NRL Electra facility (1,2). Model development is based on the Orestes excimer laser code that includes 1D plasma chemistry, 1D lasing amplification, and 3D radiation transport. It includes coupled electron kinetics and plasma chemistry for atomic, molecular, and ion species. A 0D Boltzmann code provides rates for all reactions involving electrons: collisional excitation and de-excitation, attachment and detachment of electrons to fluorine atoms and molecules as a function of two parameters: reduced beam power and gas composition (3). Time- and axial dependent species densities were obtained which are used to study the collisional and radiative processes responsible for ArF* formation and destruction. Laser parameters such as time-dependent laser intensity, amplified and spontaneous emission are studied over a range of gas pressure, peak power and composition. The calculated peak power laser efficiency is compared with experiments. * Work supported by 6.1 Base Program. (1) M. F. Wolford et al., HEDP 20 (2020) 30061-6. (2) M. C. Myers et al, 2019 IEEE Pulsed Power and Plasma Sci. Conf., pp. 1-4. (3) G. M. Petrov et al., JAP 122 (2017) 133301. DISTRIBUTION A. Approved for public release: distribution unlimited. [Preview Abstract] |
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NP14.00002: PIC and Hybrid Simulations of SRF Cavity Plasmas using VSim Jarrod Leddy, Ben Cowan, Peter Stoltz, Ilya Zilberter, John Cary Superconducting radio frequency (SRF) cavities are utilized for acceleration in particle accelerators, but impurities on the surface of the cavity can cause arcing and therefore lower the maximum obtainable fields inside the cavity. Plasmas can be used to remove these impurities, but their formation and behavior is not well understood. We have performed electromagnetic particle-in-cell simulations using VSim to investigate the plasma formation via ionization cascade using a Monte Carlo collision framework. These simulations explore the EM power threshold for plasma ignition at experimentally relevant background gas pressures, and we compare them with experimental data. In addition to plasma formation, the behavior of the plasma at long time scales is also of interest. PIC simulations are too expensive for any time scale longer than hundreds of nanoseconds, so a GPU capable hybrid model was implemented in VSim. Such a model treats the ions as kinetic species and approximates the electrons as a fluid with source terms determined by the previously conducted PIC simulations of the plasma formation. We will describe the model implementation, show benchmarks, and present preliminary results for the simulations in the cavity geometry. [Preview Abstract] |
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NP14.00003: Semi-empirical Numerical Model of RF-driven Nitrogen Discharge. Alexander Hyde, Oleg Batishchev Nitrogen discharges are broadly used in science and technology, as N2 is the primary atmospheric gas and the base of many important chemicals due to its strong covalent bond. We report on the development of a power-mass balance model of an axysymmetrical RF discharge [1-2] that takes into account the dominant physical processes: axial and radial transport, gas ionization and excitation, wall loses, etc. Being a molecular gas, it brings additional complexity to a robust numerical model. We include emission from several of the strongest systems that we have detected in experiment: 1st and 2nd positive, 1st negative and Lyman--Birge--Hopfield. [1] A. Hyde, Andrew S. Taylor, and Oleg V. Batishchev, IEEE Transactions on Plasma Science, 46(2):395--405, February 2018. [2] A. Hyde and O. Batishchev, Plasma Medicine, 8(1): 45--55, 2018. [Preview Abstract] |
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NP14.00004: Deriving Scaling Laws for Transition from Avalanche to Streamer Discharge Haoxuan Wang, Amanda Loveless, Allen Garner Recent theoretical studies have derived a single theoretical framework examining the transitions between quantum space-charge limited emission (SCLE), SCLE at vacuum (Child-Langmuir law), SCLE with collisions (Mott-Gurney law), field emission, and Paschen's law (PL) [1]. Reducing gap size to microscale causes a deviation from PL since Townsend avalanche no longer drives breakdown. Increasing gap size or pressure causes an avalanche to streamer transition (AST). This study explores the feasibility of deriving simple scaling laws accounting for AST to incorporate into the existing breakdown/emission theoretical framework [1]. We apply Meek's criterion to predict the conditions necessary to achieve AST for microscale gaps of air and calculate the necessary overvoltage using PL. We also nondimensionalize Meek's criterion to assess the feasibility of deriving a universal theory for breakdown transition. Calculations of ion head radius and space charge field needed for AST and the resulting implications on theoretical development and device design will also be discussed. [1] A. M. Loveless, et al., Trans. Am. Nucl. Soc. 121, 399-401 (2019). HW gratefully acknowledges support from a Purdue Ross Fellowship. [Preview Abstract] |
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NP14.00005: Measurement of material recession and shock standoff in plasma windtunnel using neural nets Magnus Haw, Alexandre Quintart Arcjets are plasma wind tunnels used to test the performance of heatshield materials for spacecraft atmospheric entry. These facilities present an extremely harsh flow environment with heat fluxes up to $10^9$ W/m$^2$ for up to 30 minutes. The plasma is low-temperature ($\sim$1 eV) but high pressure ($>$ 10 kPa) creating high-enthalpy supersonic flows similar to atmospheric entry conditions. Typically, material samples are measured before and after a test to characterize the total recession. However, this does not capture time-dependent effects such as material expansion and non-linear recession. This work will present new analysis of arcjet test videos which measure both the time-dependent 2D recession of the material samples and the shock standoff distance. New results showing non-linear time-dependent effects will be highlighted. The material and shock edges are extracted from the videos by training and applying a convolutional neural network. Due to the consistent camera settings, the machine learning model achieves high accuracy ($\pm$ 2 px) relative to manually segmented images with only a small number of training frames (80). The new results will be discussed in the context of temperature dependent plasma-surface interaction. [Preview Abstract] |
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NP14.00006: Continuous Wave Laser Induced Fluorescence with a Fast Camera Mitchell Paul, Earl Scime Typically, planar laser induced fluorescence (PLIF) systems combine a high intensity pulsed laser with a gated camera to obtain 2D images of the relative density of the interrogated species in a region of interest. In a low temperature plasma, the large linewidth of a pulsed laser prevents PLIF measurements of the velocity distribution of massive species. Without velocity-resolved PLIF images, the species temperature or bulk flow cannot be extracted from the PLIF image. Single-point LIF measurements and PLIF measurements with a camera can provide temperature and flow measurements if a continuous wave (CW) laser is used. However, interrogating 2D planes of the plasma requires thousands fewer measurements when acquired with a camera instead of single-point measurements. Here, we present PLIF measurements of the temperature and flow of argon ions in a low temperature plasma using a modulated, narrow linewidth, CW laser. The fluorescent emission is acquired with a fast, camera and the laser light is spread into a thin sheet so that an entire plane of the plasma is imaged at each interrogation wavelength. Fourier analysis is conducted on each pixel of the images to separate the fluorescent emission from the background light. Replacing the PMT with the camera as the detector dramatically reduces the time needed to measure an entire plane of the plasma. Argon ion temperatures and bulk flow maps are reported in a helicon plasma source and standard single-point measurements provide the validation of the PLIF measurement. [Preview Abstract] |
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NP14.00007: Measurements of electric potential in a collisional plasma generated by the carbon arc Nirbhav Chopra, Yevgeny Raitses In an atmospheric pressure anodic carbon arc discharge used for nanomaterial synthesis, carbon material is introduced into the arc by the ablation of the graphite anode [1]. The anode ablation depends on the power balance at the anode, which is influenced by whether the anode sheath is electron-repelling (negative anode sheath) or electron-attracting (positive anode sheath) [2, 3]. In this work, we attempt to determine the anode sheath sign by measuring the floating potential in the arc using a fast swinging Langmuir probe. The plasma potential is deduced from the floating probe measurements. The effect of arc motion on the measured probe potential is taken into account by correlating the measured probe potential with fast-frame images. The effect of ion-neutral collisions on the probe floating potential is considered in the determination of the plasma potential [4]. [1] A. J. Fetterman, Y. Raitses, and M. Keidar. \textit{Carbon}, 46, 2008. [2] V. A. Nemchinsky and Y. Raitses. \textit{Plasma Sources Sci. Technol.}, 25, 2016. [3] A. Khrabry, I. D. Kaganovich, V. Nemchinsky, and A. Khodak. \textit{Phys. Plasmas}, 25, 2018. [4] P. Bryant. \textit{J. Phys. D: Appl. Phys.}, 36:2859, 2003. [Preview Abstract] |
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NP14.00008: Simulating Dynamic Triggering for Spark Gap Switches Pierre Gourdain, Imani West Abdallah, Marissa Adams, Matthew Evans, Hannah Hasson, James Young, Daniel Mager In LTD technology, high-pressure spark gap switches are vital to creating triggering events on the nanosecond timescale. While this architecture requires many switches to function synchronously in parallel, present designs have shown limitations, mostly due to their lack of specification toward LTD's. These limitations include high inductance and excessive etching on the electrodes of the switch. To reduce the overall inductance in and minimize maintenance on HADES (High Amperage Driver for Extreme States), we have designed a spark gap, ball switch that addresses these disadvantages. COMSOL studies (2-D and 3-D) of dynamic triggering events (DC and Pulsed) at $+$/- 100 kV are used to investigate potential current paths inside of the switch cavity. Our COMSOL studies will inform changes to our design before testing our switches in a multi-brick system. [Preview Abstract] |
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NP14.00009: High-voltage DC flashover and punch-through of additively manufactured materials in pressurized air and dielectric oil for pulsed-power applications Ian Bean, Thomas Weber, Colin Adams, John Boguski Surface flashover and punch-through of dielectric materials are primary limiting factors for high-voltage, low-inductance pulsed-power drivers. The use of additively-manufactured (AM) materials as high-voltage insulation can enable rapid design iteration of complex geometries that are difficult to machine with standard techniques. We investigate the applicability of a range of AM materials for the purpose of high-voltage insulation in compressed air and dielectric oil environments. Details on these investigations are presented and compared to a variety of conventionally-manufactured insulating materials. [Preview Abstract] |
(Author Not Attending)
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NP14.00010: Analytical and Numerical Characterization of a One and Two-Dimensional Plasma Photonic Crystal with Smooth Variations in Density W. R. Thomas, U. Shumlak Plasma photonic crystals (PPCs) have the potential to significantly expand the capabilities of current microwave filtering and switching technologies by providing high speed ($\mu$s) control of energy band-gap/pass characteristics in the GHz through low THz range. Furthermore, plasma-based devices can be used in higher power applications than their solid-state counterparts without experiencing significant changes in function or incurring damage. The majority of numerical and theoretical investigations into PPCs are based on metallic PC theory, and make the simplifying assumption of uniform density plasmas. In practice, most methods of generating repeatable, controllable plasmas have density gradients arising either from diffusion or wall effects. In this investigation we use an analytically derived dispersion relation and a multi-fluid plasma model, implemented in the WARPXM computational framework, on a plasma with both one and two-dimensional density variations. The two methods are used to understand the relationship between important dimensionless parameters (a lattice normalized plasma frequency, density variation amplitude, and the peak normalized density gradient) and electromagnetic wave dispersion characteristics. [Preview Abstract] |
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NP14.00011: Development of Atmospheric Pressure Plasma Jets for PFAS Remediation Adam D. Light, Dzafer Camdzic, B. Logan Henning, Shalese M. Lovell, Anni Zettl Polyfluorinated alkyl substances (PFAS) are emerging as a ubiquitous and difficult to remove contaminant in drinking water. The strength of the carbon-fluorine bond makes it extremely energy intensive to break apart and mineralize these compounds. Non-equilibrium plasma at atmospheric pressure is a promising treatment technique for PFAS contamination because hot electrons and active radical species can be produced with minimal gas heating. While various plasma discharge types have been investigated as remediation tools, atmospheric pressure plasma jets (APPJ) have not been studied systematically in the context of PFAS. Our new lab at Colorado College is being built to study the application of these jets to PFAS contamination in collaboration with the Fountain Valley Water Project. I will present PFAS-specific design goals for our plasma jets, describe our targeted diagnostic measurements, and show our progress to date. [Preview Abstract] |
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NP14.00012: Numerical Investigation of Counter-Streaming Ion Tails from Current-Carrying Instabilities in a Hollow Cathode Plasma Alexander Vazsonyi, Benjamin Jorns, Iain Boyd Erosion of thermionic hollow cathode keepers presents a challenge for Hall effect and gridded ion thrusters that are used for spacecraft propulsion. Within the past decades, the source of this erosion has been tied to ion heating by current-carrying instabilities, namely the ion acoustic instability. Existence of the ion acoustic instability in the cathode plume is based on a wealth of supporting experimental and numerical evidence, making its presence highly likely. Recent 1D kinetic simulations have demonstrated that, for sufficiently large electron drifts, current-carrying instabilities are capable of generating high energy ion tails in the direction opposite of the electron current; theoretically, these ions would then impinge on the cathode. The mechanism which produces these counter-streaming ion tails is not clear, though it was proposed that reflection-driven reverse-streaming ion acoustic waves may be the culprit. Thus, this work aims to closely analyze 1D1V Vlasov-Poisson simulations of current-carrying plasmas to determine whether counter-streaming ion acoustic waves are the plausible driver of these high energy ion tails. [Preview Abstract] |
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NP14.00013: Spectral Characterization of Hall Effect Thruster Exhaust. Oleg Batishchev, Alexander Hyde, James Szabo Extreme-UV spectra of a Hall Effect Thruster operating on Xe gas are collected and emission lines of various ions, neutrals and possible impurities are identified. Next, FUV-MUV spectra are examined for notorious boron nitride lining erosion products, and compared to previous results [1,2]. Finally, a recently developed UV-VIS high-resolution system [3] is applied to measure the axial velocity of Xe$+$ ions in the plasma plume at different spatial locations. Different operational regimes are compared. [1] William A. Hargus, Jr. Joshua Strafaccia, AIAA-2005-3529 Joint Propulsion Conference, Tucson, AZ. [2] M. Celik, O. Batishchev, M.Martinez-Sanchez, Vacuum 84(9), April 2010, 1085-1091. [3] A. Hyde, O. Batishchev, Review of Sci. Instr. 91(063502), June 2020. [Preview Abstract] |
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NP14.00014: 2D Spatial Profiles of Ion Velocity Distribution Functions in Rotating Magnetic Field Plasma Acceleration Method Takerku Furukawa, Daisuke Kuwahara, Shunjiro Shinohara Electrodeless rf (radio frequency) plasma propulsion system is a promising way to overcome degradation of thrust performance and limitation of its operational life time because of erosion of the electrodes (grids), which can be seen in conventional electric propulsion systems such as ion gridded engine and Hall thruster. Rotating Magnetic Field (RMF) plasma acceleration method [1,2] is one of the electrodeless concepts and is expected to enhance performance by means of additional plasma acceleration [1], i.e., electromagnetic force. This RMF method drives an azimuthal electron current owing to Hall-term effect, and the additional force is generated in the presence of the external divergent magnetic field. To demonstrate our proposed RMF thruster concept, two-dimensional spatial profiles of ion velocity distribution functions were measured by using Laser Induced Fluorescence (LIF) method [3]. In this conference, these spatial profiles will be reported, showing the RMF plasma acceleration effect in comparison to the profiles without the RMF application. [1] S. Shinohara et al, IEEE Trans. on Plasma Sci. Vol. 42 (2014) 1245. [2] T. Furukawa et al, Phys. Plasmas, Vol.24 (2017) 043505, Vol.26 (2019) 033505, AIP Adv., Vol.7 (2017) 115204, and Rev. Sci. Instrum., Vol.89 (2018) 043505. [3] Y. Tanida et al, T. Jpn. Soc. Aeronaut. S., Vol.14 (2016) Pb7. [Preview Abstract] |
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NP14.00015: Development and Characterization of a LaB$_\mathbf{6}$ Heaterless Hollow Cathode with an Open-Ended Emitter Trenton R. Brewer, Prachi L. Jain, Matthew J. Carrier, Alex W. Nikrant, Colin S. Adams Hollow cathodes have been investigated as electron sources for plasma ionization and beam neutralization in electric thrusters since the 1960s. Heaterless versions have the potential to avoid the start-up times and power expenditures associated with external heating sources. A modular, low-current heaterless hollow cathode (HHC) has been developed to study operating mode transitions and sheath physics and to provide an electron source for a future electric thruster. The cathode operates in a triode configuration, consisting of an open-ended $\mathrm{LaB}_6$ thermionic emitter, an orificed tantalum keeper, and a stainless steel flat-plate anode. Voltage and current characteristics recorded during operation with both argon and krypton gas show two distinct discharge modes. Plasma density and temperature in the region between the emitter and keeper are inferred from measured discharge current, emitter-keeper voltage, and mass flow rate using a current-conservation and power balance model. [Preview Abstract] |
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NP14.00016: On the Addition of Electron Inertia to the Computational Modeling of the Ion Acoustic Shock Robert Lilly, Robert Martin The ion-acoustic shock serves as an excellent benchmark for comparing various kinetic and particle plasma algorithms. AFRL/RQRS comparisons between fluid, Vlasov, and PIC plasma models have made use of the Boltzmann equilibrium for the electrons, thereby avoiding the need to capture electron timescales. Though internally consistent, the validity of assumptions inherent in the Boltzmann equilibrium model have not been rigorously explored in RQRS test cases. This work first reintroduces steady state electron inertia into the electron equilibrium model to enable study of high electron drift as found in hall thrusters. This equilibrium is then used to compare two approaches to the problem. In the first, the ion fluids are advanced using Euler equations, but the electron densities are determined using a Poisson-Boltzmann solve to determine both the scalar electric potential and the electron density that are self-consistent with the derived equilibrium. These results are compared to a full two Euler fluid simulation, where both the electron and ion plasma fluid species are modeled using Euler equations, and are coupled via a direct Poisson solve for the scalar electric potential. It is observed that the match between the two models is excellent, with and without the electron drift. [Preview Abstract] |
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NP14.00017: Formation of Reactive oxygen species in atmospheric pressure plasma jet. Surabhi Jaiswal, Evan Aguirre, G Veda Prakash We report on the characterization of an argon atmospheric pressure plasma jet with strong emission of atomic oxygen along with O$^{\mathrm{1}}$S emission. The plasma jet was formed with pure argon gas without the need for secondary gases such as O2 or N2. The O$^{\mathrm{1}}$S emission was continually present for a variety of parameters including: argon flow rate, electrode gap, and applied voltage. However, a threshold is found in all these parameter for the maximum atomic oxygen components in the plasma. The plasma plume length was in excess of 2.5 cm and was found to produce a variety of reactive species (OH, O, N2, and N$^{\mathrm{+2}})$ that are important for biomedical and technological applications. The chemical formulation for the formation of reactive oxygen species in pure argon plasma has been established and their effect on the biological and other industrial applications has been discussed. [Preview Abstract] |
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