Bulletin of the American Physical Society
73rd Annual Gaseous Electronics Virtual Conference
Volume 65, Number 10
Monday–Friday, October 5–9, 2020; Time Zone: Central Daylight Time, USA.
Session FT3: Magnetized and Dense PlasmasLive

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Chair: Arthur Dogariu, Princeton University 
Tuesday, October 6, 2020 8:00AM  8:15AM Live 
FT3.00001: Multimegawatt terahertz emission of a magnetized plasma with strong density gradients under the injection of a kiloampere REB Andrey Arzhannikov, Vladimir Annenkov, Ivan Ivanov, Petr Kalinin, Alexandr Kasatov, Sergey Kuznetsov, Konstantin Kuklin, Maxim Makarov, Konstantin Mekler, Sergey Popov, Andrey Rovenskikh, Denis Samtsov, Evgeny Sandalov, Stanislav Sinitsky, Vasily Stepanov, Igor Timofeev, Vladimir Glinskiy Injection of a relativistic electron beam (0.8 MeV, 10 kA, 5 \textmu s) into a magnetized plasma column has been actively studied last years at the GOLPET facility as a method for generating highpower tunable terahertz radiation. Recent experiments [1] have shown that the power of radiation flux along the plasma column at the fundamental plasma frequency harmonic achieves 4 MW in case of strong radial plasma density gradients. We report that creating a low density plasma gap between the plasma column end and a graphite collector for the Ebeam allows us to reach the power level of 10 MW in the radiation flux. Theoretical ideas about mechanisms of enhanced THz generation in the beamplasma system will be also presented. The work was supported in part by the Russian Science Foundation (project no.191200250). [1] Arzhannikov A Vet al. \textit{Plasma Physics and Controlled Fusion }\textbf{62,} 045002 (2020) [Preview Abstract] 
Tuesday, October 6, 2020 8:15AM  8:30AM Live 
FT3.00002: Modeling of extreme density plasma by nanosecond pulsed discharge with secondstage wave heating Evrim Solmaz, Laxminarayan L. Raja Nonequilibrium high pressure discharges of plasma densities \textasciitilde 10$^{\mathrm{14}}$10$^{\mathrm{15}}$ cm$^{\mathrm{3}}$ have been characterized well through experiments and modeling. However, the mechanisms that generate plasma densities of \textgreater 10$^{\mathrm{19}}$ cm$^{\mathrm{3}}$ bordering on warm dense matter regimes are not well understood. We hypothesize that the anomalously high plasma densities in nanosecondpulsed discharges are driven by 1) transient streamer propagation leading to extreme electric fields and 2) extreme cathode sheath electric fields causing runaway emission. In this work, we improve our existing computational fluid model for simulating these dense nanosecondpulsed discharges at high pressures. An obstacle to predicting streamer transition to dense mode is a timestep restriction, which will be alleviated by a fully implicit time integration scheme for the electronPoisson equation system. The lowering of ionization potentials will be addressed by modified rate coefficients for ionization reactions. The ion correlation effects, which become significant in nonideal plasmas, will be addressed by reformulating our heavy species energy equations to account for the ionion Coulomb interactions. Also, corrections will be made for the enhanced charged particle collision cross sections, which will modify the transport properties. [Preview Abstract] 
Tuesday, October 6, 2020 8:30AM  8:45AM Live 
FT3.00003: Friction and electrical conduction in strongly magnetized plasmas Scott Baalrud, Trevor Lafleur Frictional drag on a particle due to its interaction with the medium through which it travels is commonly expected to act antiparallel to its velocity. Recent work has shown that a qualitatively different effect arises in strongly magnetized plasmas, whereby the friction force gains a transverse component that is perpendicular to the velocity vector in the plane formed by the velocity and magnetic field vectors [1]. The transverse force arises due to the manner in which the Lorentz force influences the dielectric polarization of the background plasma. It is large when the electron gyrofrequency significantly exceeds the plasma frequency. It causes the gyroradius of fast particles to increase, and that of slow particles to decrease faster than in its absence. The alteration of single particle motion leads to qualitatively new macroscopic transport properties. As an example, we show that it leads to a new transverse component of electrical resistivity that alters the flow of current in response to an applied electric field. [1] Lafleur and Baalrud, PPCF 61, 125004 (2019). [Preview Abstract] 
Tuesday, October 6, 2020 8:45AM  9:00AM Live 
FT3.00004: Investigation on electron drift motions of low temperature DC plasmas in Magnetic Xpoint sIMUlator System, MAXIMUS. Yegeon Lim, Bin Ahn, Yong Sung You, Youngchul Ghim We present electron drift motions in MAXIMUS (MAgnetic Xpoint sIMUlator System), where low temperature DC plasmas with tokamaklike poloidal magnetic fields are generated. MAXIMUS is a linear multidipole chamber (2.0m long and 0.6m in diameter) with a pair of axially installed watercooled copper tubes generating tokamaklike poloidal magnetic fields by running DC currents (up to 1kA each) through them. We use negatively biased hot thoriated tungsten filaments to generate DC plasmas, and the filaments are placed around the upper copper tube. Such a novel plasma source generates dense plasmas in the core region (around the copper tube) with a radial electron pressure gradient whose scale length is approximately 1 cm. It is apparent that the electron drift motions due to gradB and curvature of the fields are playing a significant role as the plasmas are only generated in the direction of the electron drifts. Using a onesided planar Langmuir probe, we measure and report electron velocity distribution functions including the effects of gradB and curvature drifts which lead to asymmetric distribution functions in the velocity space. [Preview Abstract] 
Tuesday, October 6, 2020 9:00AM  9:15AM Live 
FT3.00005: Evolution of heavy nucleus acoustic shocks in white dwarfs Kuldeep Singh, N. S. Saini There has been a large interest in studying the relativistic degenerate dense plasmas due to its existence in interstellar compact objects, such as white dwarfs, neutron stars. It is notable that the basic constituents of white dwarfs are mainly positively and negatively charged heavy elements like carbon, oxygen, helium with an envelope of hydrogen gas. The existence of heavy elements (positively and negatively) is found to form in a prestellar stage of the evolution of the universe, when whole matter was compressed to extremely high densities. We have investigated heavy nucleusacoustic (HNA) shock waves and solitons in a degenerate relativistic magnetorotating quantum plasma (DRMQP) system containing relativistically degenerate electrons and light nuclei, and nondegenerate mobile heavy nuclei. Only positive potential HNA shock waves and solitons have been found in consonance with the satellite observations. It is observed that the heavy nucleus viscosity is a source of dissipation, and is responsible for the formation of HNA shock structures. It is shown that the combined effects of external magnetic field strength, rotational frequency and obliqueness significantly modify the basic properties of the HNA shock waves and solitons. It is intensified that the combined effects of magnetic field and Coriolis force are not considered in degenerate relativistic plasma system. The results should be utilitarian to understand the characteristics of nonlinear excitations in degenerate relativistic magnetorotating quantum plasma which is present in astrophysical compact objects especially in white dwarfs [Preview Abstract] 
Tuesday, October 6, 2020 9:15AM  9:30AM 
FT3.00006: Theoretical and numerical characterization of driftwave instabilities in magnetized discharges Andrea Marcovati, Mark Cappelli Gradientdriven driftwaves form and propagate in nonuniform magnetized plasmas. In previous work we presented a linear model that describes their dynamics consistent with what is seen in small magnetron configurations. These instabilities (100 kHz  800 kHz) develop in the form of spokelike coherent structures propagating azimuthally and transitioning between coherent modes when varying discharge voltage. Between modes the fluctuations are much more stochastic. Experiments conducted to characterize these stochastic regimes show energy concentration at multiple discrete frequencies, generally higher than the linear ones (\textgreater 1MHz). Analyses of the power spectra show interactions between these frequencies consistent with threewave mixing processes, suggesting nonlinear energy transfer. To better understand these experimental findings, we numerically integrate the nonlinear perturbation equations. In this presentation we present this nonlinear model as well as the first results, and compare these to experiments carried out which characterize the wave dispersion through measurements of fluctuationdriven current density using a finely segmented anode, providing higher wavelength resolution than in past studies. [Preview Abstract] 
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