Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session ZO05: Fundamental: Plasma Production and Diagnostic TechniquesOn Demand
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Chair: Steven Shannon, North Carolina State Room: Rooms 306-307 |
Friday, November 12, 2021 9:30AM - 9:42AM |
ZO05.00001: Meter-length table-top inductive radio-frequency plasma discharge for use in high energy density science experiments Charles D Arrowsmith, Anthony Dyson, Jon Tomas Gudmundsson, Tom Hodge, Robert Bingham, Gianluca Gregori Large-scale plasma discharges (on the order of meter-length or more) can be utilized in a variety of experiments. One example where such lengths of plasmas are necessary, is in the observation of particle beam-plasma instabilities and the emergence of coherent macroscopic structures, which are key for modelling emission from collisionless shocks. We have developed a table-top inductive radio-frequency plasma discharge which can stably sustain plasmas with electron densities of approximately 1011 cm-3. The current design is meter-length, and it can be scaled to longer lengths due to its modular design. The discharge has been assembled using a commercially-available 1 kW power supply, making it an accessible option for studying physics involving meter-length plasmas in the laboratory. We propose to use this plasma discharge design in an experiment at CERN’s HiRadMat facility, in which we will probe the magnetic field growth associated with filamentation beam-plasma instabilities of an electron-positron beam relevant to gamma ray burst (GRB) fireballs. |
Friday, November 12, 2021 9:42AM - 9:54AM Not Participating |
ZO05.00002: Long pulse measurements from a cold field emission cathode Joshua E Coleman, Madison R Howard, Steven Lidia A test bed for high perveance field-emission cathodes and photocathodes has been developed. The diode has been designed for voltages up to 500kV, has the ability to test cathode diameters < 2.5 cm, and an adjustable A-K gap from 2-8 cm. The cathode is driven by 20-Ohm, 400 kV, PFN Marx capable of providing a 2.6 μs pulse. We also have the ability to crowbar the pulse down to ~300 ns. Preliminary measurements of cathode emission at V > 200 kV and E > 60 kV/cm are presented. These consist of cathode induced light emission, extracted currents > 100 A (J > 40 A/cm2), and corresponding current density distributions downstream. Transient field emission effects are observed for t > 150 ns. A preliminary analysis of field emission effects over the 0.3-2 μs pulse length range is also presented. |
Friday, November 12, 2021 9:54AM - 10:06AM |
ZO05.00003: Kinetic simulations of the PFRC-2 using the VPIC code Mehmet S Demir, Samuel A Cohen This study concerns our recent attempts to simulate the Princeton Field-Reversed Configuration-2 (PFRC-2) heating and confinement system. The goal is to perform full-scale 3D kinetic simulations of the PFRC-2 device and investigate energy and particle flow in high-β plasmas. To model the RMF antenna, flux conservers, and mirror coils of the PFRC-2, three-dimensional kinetic simulations are performed using the VPIC particle in cell code[1]. By using appropriate length and time scales the current of each coil is defined over the relevant cells. Thus, the electric and magnetic fields induced by each coil are calculated self consistently. Finally, a fully ionized collisionless Hydrogen plasma case is studied and simulation results are discussed. |
Friday, November 12, 2021 10:06AM - 10:18AM |
ZO05.00004: Radial characteristics of magnetized plasma behind an insulating obstacle SATADAL DAS, Shantanu Karkari Interplay between external objects and plasma has enormous significance on global plasma properties. It has a relevance ranging from wake creation behind a satellite to the scrape of layer plasma region created in the shadow of a limiter in the edge of tokamak, or a low density region created behind a macroscopic object inserted in a flowing plasma column. The equilibrium properties of plasma inside the wake region depends on several factors like, the external magnetic field, charge-neutral collisions and flow of plasma. But the most important factor is the nature of the obstacle that is immersed inside a magnetized plasma column. Many fundamental research on conducting macroscopic object have been carried out to unravel its effect on charged particle transport in magnetized plasma column, but the role of insulating object has not been well understood. |
Friday, November 12, 2021 10:18AM - 10:30AM |
ZO05.00005: Studies of laser produced plasma from foam targets for future nanolithography devices and soft X-ray sources Yaoxing Wu, Xinbing Wang, Ahmed Hassanein Foam targets are expected to be more efficient candidates than solid targets for laser produced plasma (LPP) for extreme ultraviolet (EUV) and soft x-ray (SXR) radiation sources due to the expected plasma conditions that can be optimized regarding plasma opacities, volumetric heating effects, and the produced ions debris characteristics. Comparing LPP studies between Ni and Ti targets with different densities indicate that the ions in the foam target plasma have a relatively uniform distribution compared to solid targets. The average ion energy and the peak of the time-of-flight (TOF) signal decrease as the target density decreases, especially at higher laser intensities while the total charge values between foam and solid target plasma are comparable indicating a more volumetric absorption of laser energy for foam targets. Having lower ions debris energy and flux are very important to protect the expensive EUV optical collector system. The results of the mass ablation rate are consistent with the Faraday Cup (FC) signals and show more intense plasma shielding for solid target plasma. The SXR spectrum and the conversion efficiency of laser to photon energy at the required wavelength for nanolithography show similar values for solid and foam Ti targets. Similar results are expected for Sn foam target, the current leading candidate for nanolithography. These experimental results provide more insights for the laser interaction with foam targets. |
Friday, November 12, 2021 10:30AM - 10:42AM |
ZO05.00006: Neural Network Surrogates for Atomic Physics Simulations and X-ray Spectral Evaluation Derek Mariscal, Blagoje Z Djordjevic, Mike J MacDonald, Edward V Marley, Raspberry A Simpson, Tammy Ma Atomic physics simulations typically require significant computational resources to execute which significantly impacts the speed at which optimal fit parameters (density, temperature, plasma scale-length, etc.) can be deduced from experimental data. Here we develop a neural-network (NN) surrogate for the atomic physics simulations in order to very rapidly (10’s of ms) produce x-ray spectra based on these inputs. To further increase the speed of evaluation a principal components analysis is performed on the spectra in order to reduce the number of spectral datapoints (typically >1k in this work) to just 50 parameters. This is then used in tandem with a genetic algorithm for fitting the spectra to get approximate results which can then be checked with atomic physics simulations in the density and temperature range suggested by the NN-based genetic algorithm. We present the framework for this methodology and results from application of this technique for fitting temporally and spatially integrated x-ray spectra from proton-driven isochoric heating experiments performed on Omega EP. |
Friday, November 12, 2021 10:42AM - 10:54AM |
ZO05.00007: Imaging Transient X-rays Caused by Suprathermal Particles From A Laboratory Plasma Jet Yi Zhou, Paul M Bellan Transient 6 keV x-ray bursts having a duration of about one microsecond are detected in a laboratory plasma jet with 2 eV electron temperature. To investigate how these suprathermal x-rays are generated, a 50-channel 1 dimensional PIN-diode-based x-ray coded aperture camera has been developed to locate the source of x-ray emissions. Preliminary pinhole x-ray images have confirmed a localized x-ray source within the plasma jet. To identify the exact location of the source, we are currently working on obtaining images with a higher signal-to-noise ratio and better spatial resolution with a coded aperture. Since x-rays are detected when the plasma jet is choked and broken by Rayleigh-Taylor ripples, we suspect the x-ray source is located at the breaking position. We are hoping to confirm this suspicion by overlaying x-ray images and visible light images of the plasma jet. |
Friday, November 12, 2021 10:54AM - 11:06AM |
ZO05.00008: Single-shot spatio-temporal visualization of plasma and optical nonlinearity via single-shot frequency-domain holography Dennis Dempsey, Garima C Nagar, Jack W Agnes, Russell Berger, Bonggu Shim We observe the ultrafast dynamics of solids and gases under intense femtosecond light in a single shot using Frequency Domain Holography (FDH) [1-3]. FDH is a time-resolved visualization technique that utilizes a pump pulse and two chirped laser pulses (reference and probe) for ultrafast phase measurements. Single-shot visualization of laser-matter interactions will allow for increased understanding of nonlinear optical phenomena such as Raman-induced extreme spectral broadening [4], filamentation [5], and plasma generation and recombination [3]. |
Friday, November 12, 2021 11:06AM - 11:18AM |
ZO05.00009: Stimulated excitation of thermal diffusion waves in a magnetized plasma pressure filament Richard D Sydora, Scott G Karbashewski, Bart G Van Compernolle, Matthew J Poulos Results are presented from basic heat transport experiments using a magnetized electron temperature filament that behaves as a thermal resonator. The experiments were carried out in the Large Plasma Device (LAPD) at the Basic Plasma Science Facility (BaPSF), University of California, Los Angeles. 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 create an oscillating heat source capable of driving large amplitude electron temperature oscillations. Langmuir probes are used 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 and cross-field thermal diffusivity. |
Friday, November 12, 2021 11:18AM - 11:30AM |
ZO05.00010: The Effect of Cerium Surface Oxidation on Plasma Plume Geometry Imaged After Nanosecond Laser Ablation David Weisz, Alexander Auner, Jonathan C Crowhurst, Lauren Nagel, Kim Knight The effects of surface chemistry on plasma formation and expansion after laser ablation are of interest to applications from metallurgy to astrophysics. In this work, we investigated cerium plasma plume geometry as a function of surface oxidation by imaging the plasma emission. Polished cerium was ablated using a Nd:YAG nanosecond pulsed laser. Images were stitched from a series of EMCCD gated delay times from 10 ns to 3 µs after pulse with the imaging repeated as the surface oxidized for 30 min, 1 hour, 1.5 hours, 3 hours, etc. up to a week later. Images of the plume compared at different oxidation states for the same CCD delay time show significant changes of both plasma length and overall geometry. As the metal surface oxidized, the velocity of the expanding shockwave was calculated and showed a decrease in velocity as the metal surface oxidized. |
Friday, November 12, 2021 11:30AM - 11:42AM |
ZO05.00011: An inertial confinement fusion plasma based cross-calibration of the deuterium-tritium γ-to-neutron branching ratio Justin Jeet, Alex B Zylstra, Michael S Rubery, Yongho Kim, Chad Forrest, Vladimir Y Glebov, Colin J Horsfield, Aaron M McEvoy, Hans W Herrmann The deuterium-tritium (D-T) γ-to-neutron branching ratio [3H(d,γ)5He/3H(d,n)4He] has been determined previously under inertial confinement fusion (ICF) conditions and in beam-target based experiments. In the former case, neutron-induced backgrounds are mitigated compared to the latter due to the short pulse nature of ICF implosions and the use of gas Cherenkov γ-ray detectors. An added benefit of ICF based measurements is the ability to achieve lower center of mass energies as compared to accelerators. Previous ICF based experiments however report a large uncertainty in the D-T γ-to-neutron branching ratio of ~48%, which arises from the necessity of an absolute detector calibration and/or a cross calibration against the D-3He γ-to-proton branching ratio. A more precise value for the branching ratio based on data taken at the OMEGA laser facility is reported here, which relies on a cross-calibration against the better known 12C neutron inelastic scattering cross section. A D-T branching ratio value of (4.81 ± 0.61) × 10−5 is determined by this method. |
Friday, November 12, 2021 11:42AM - 11:54AM |
ZO05.00012: Space-Charge Limited Current: Extensions to Non-planar, Multidimensional, and Crossed-field diodes Sree Harsha N R, Adam M Darr, Allen L Garner Space-charge limited current (SCLC), first derived over a century ago by Child and Langmuir for one-dimensional (1-D) planar diodes, represents the maximum current that can flow in a diode and remains a critical limit for vacuum device operation [1]. We have used variational calculus (VC) [2] and conformal mapping [3] to derive analytic solutions for SCLC for more complicated geometries. We extend this approach to multidimensional non-planar diodes by deriving a general relationship dependent on only diode vacuum electric potential and capacitance. We apply this approach to extend SCLC for 1-D planar diodes with an external magnetic field perpendicular to the electric field [4] to non-planar and multidimensional diodes. This approach permits rapid screening of SCLC for more realistic diodes to guide further simulations and experimental studies. |
Friday, November 12, 2021 11:54AM - 12:06PM |
ZO05.00013: Empirically extending Child-Langmuir theory to a thermal electron distribution Jesse M Snelling, Gregory R Werner, John R Cary While the self-consistent potential and current flow in a parallel plate diode can be analytically calculated in the 1D limit for a cold beam of electrons, this work explores the non-trivial extension to finite temperature. The input parameter space (injected current density, potential boundary conditions, gap distance, beam velocity, and temperature) is reduced to just three dimensionless parameters. A systematic sweep over these three parameters is performed to explore space charge effects on the average anode current, as well as to characterize the oscillatory behavior expected near the space charge limit. The results from 1D simulation allow the construction of a simple, empirical model for the diode characteristics for the case of a thermal electron distribution. This model can be applied to nanoscale vacuum channel transistors (NVCT). Specifically, we have shown using full-device 3D PIC simulations that NVCT arrays comprising a large number of uniform tips field-emitting into a large gap are practically one dimensional as far as space charge effects are concerned, meaning the gap environment is well described by the aforementioned empirical model for diodes. |
Friday, November 12, 2021 12:06PM - 12:18PM |
ZO05.00014: Inclusion of charge-exchange dynamics in a collisional-radiative model for magnetic fusion plasmas Prashant Sharma, Xianzhu Tang The charge-exchange processes are usually not included in the collisional-radiative (CR) model of atomic processes in plasmas. However, they are known to be important for impurity dynamics in magnetic fusion plasmas, for both steady-state power exhaust and disruption mitigation. One particular interesting scenario for disruption mitigation is the use of hydrogen injection to purge high-Z impurities in the post-thermal-quench plasma that has already completed the Ohmic-to-runaway current conversion. This is previously understood as the result of enhanced recombination due to the additional electron cooling. Here we investigate the additional role of charge-exchange, both with the same species and between different species. To this end, we first present the single electron total and state selective charge-exchange cross-sections for Nq+ (q = 1-7), Neq+ (q = 1-10), Arq+ (q = 1-18) colliding with H and H2 in ground state using the multichannel Landau-Zener and molecular orbital close-coupling methods. The main emphasis here is to systematically explore the charge-exchange dynamics in the low-energy regime typical of a post-thermal-quench plasma. The calculated charge-exchange rate coefficients will be incorporated in the extended version of the CR program to study the ionization balance of impurity ions. More broadly, this CR model with charge-exchange will also be important to determine the impurity transport fluxes and the electron energy dissipation. The radiative power in this mixture of light and heavy atoms can also be quantified for the purpose of both plasma cooling and runaway current dissipation. |
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