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 GP16: Poster Session: Fundamental Plasmas: Waves and Instabilities (9:30am  12:30pm)On Demand

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GP16.00001: Dupree diffusion effect on the spacecharge wave in a kappa distribution plasma column MyoungJae Lee, YoungDae Jung The diffusion effects on the dispersion equations of ionacoustic spacecharge wave in a Lorentzian plasma column composed of nonthermal turbulent electrons and cold ions are investigated based on the analysis of normal modes and the separation of variables. It is found that the real portion of the wave frequency of the spacecharge wave in a Maxwellian plasma is greater than that in a Lorentzian plasma. It is also found that the magnitude of the damping rate of the spacecharge wave decreases with an increase of the spectral index of the Lorentzian plasma. It is also shown that the magnitude of the scaled damping rate increases with an increase of the Dupree diffusion coefficient. Moreover, the influence of the nonthermal character of the Lorentzian plasma on the damping rate is found to be more significant in turbulent plasmas with higher diffusion coefficient. The variations of the wave frequency and the growth rate due to the characteristics of nonthermal diffusion are also discussed. [Preview Abstract] 

GP16.00002: A Kinetic Simulation of Ponderomotive Interactions between Reflecting Alfv\'en Waves and Particles Kendra Bergstedt, Jonathan JaraAlmonte, Hantao Ji Alfv\'en waves propagating through inhomogeneous media generate ponderomotive forces which can accelerate charged particles. This process is important throughout space and astrophysical plasma physics, contributing to pressure balance in molecular clouds and the acceleration of heavy ion species out of Earth’s ionosphere. In particular, the ponderomotive force can cause an abundance (or depletion) of heavy ions with first ionization potential (FIP) below 10 eV in a star's corona compared to its photosphere, which is known as the FIP (or inverse FIP) effect. We present kinetic simulations of an Alfv\'en wave propagating from a collisionless regime and reflecting at a higherdensity cutoff. The energization of minority ion species is compared to observations of the FIP and inverse FIP effect. Propagationangledependent interactions are investigated. The simulations are performed with varying collisionalities and results are compared to MHD simulations to determine the importance of kinetic effects. [Preview Abstract] 

GP16.00003: Simulation of quasilinear theory with highorder discontinuous Galerkin method Daniel Crews, Uri Shumlak Quasilinear theory is one of the simplest reduced models for collisionless plasma turbulence. Its similarity to Reynolds averaging suggests using the coupled quasilinear kinetic and wave kinetic equations as a model for subgridscale physics in reduced kinetic simulations. This work investigates such a reduced model numerically. After splitting between resonant and nonresonant interactions, diffusion coefficients from the classic BohmGross dispersion relation are derived analytically and utilized. Results are compared to VlasovPoisson simulations. These numerical experiments are conducted using a highorder parallelized nodal explicit RungeKutta discontinuous Galerkin method, with benchmark results given for the linear advectiondiffusion equation on a finiteinterval. [Preview Abstract] 

GP16.00004: Kineticscale instability in an oscillatory electrostatic equilibrium Fabio Cruz, Thomas Grismayer, Luis O Silva In traditional electrostatic plasma equilibrium, small amplitude electric field perturbations are screened due to charge/current imbalances. In this work, we study an electrostatic equilibrium where the plasma electric field is of nonnegligible amplitude. In this equilibrium, the plasma drives a current that reverses the electric field with a frequency that matches the plasma frequency. We derive the plasma dispersion relation from the linearized Vlasov equation, and show that this equilibrium has an infinite number of unstable modes. We identify the instability criterion and the typical growth rate of this instability. All analytical results are confirmed with simulations performed with the particleincell code OSIRIS for a variety of equilibrium distribution functions for a pair plasma. A relativistic generalization of the instability is presented, and applied to a hot, relativistic pair plasma equilibrium relevant for the late stages of pair cascades in pulsar magnetospheres. The role of this instability in the damping of the equilibrium electric field is also discussed in this context. [Preview Abstract] 

GP16.00005: Hot plasma waves in a timevarying plasma flow Min Uk Lee, JeongYoung Ji, Gunsu S Yun Excitations of electromagnetic (EM) waves in magnetically confined plasmas are often coincident with a timevarying plasma flow. Examples of abrupt generation of a localized plasma flow include the burst of edge localized mode (ELM) and the explosion of coronal loops in the solar surface. This work aims to investigate the wave dynamics in the existence of a background timevarying flow. The simplest model of the background flow that can be deduced from the fluid equations is a cold wave. To derive the wave dispersion relation, we decompose the particle trajectory into a timeaverage drift, the cold wave motion, and the cyclotron motion. Adopting the method of characteristics along the particle trajectory in the background flow and an EM field, we integrate the linearized Vlasov equation to obtain the perturbed distribution function. Then we take the first moment of the distribution function to obtain the perturbed current density and combine with Maxwell’s equations to derive a generalized hot plasma wave dispersion relation. Since the cold wave frequency is determined by the wavelength, the characteristic scale length of the flow phenomena determines the spectrum of coupled waves. The analytic dispersion relations are shown and corroborated by the 1D particleincell simulation. [Preview Abstract] 

GP16.00006: Bispectral Analysis of Unstable Broadband Cyclotron Waves: Identity of the parent waves and fraction of power associated with threewave coupling M Koepke, R Stauber The application of bispectral analysis to the study of nonlinear interactions was demonstrated by a comparison of computed quantities with results from model equations found in the literature: the amplitude and phase of coupling coefficients, the power transfer function, the fraction of power associated with nonlinear coupling, and the identification of waves involved in a quadratic coupling interaction. Two parent waves were distinguished from the daughter wave in this threewave interaction. These results, as well as the values computed from a MonteCarlo simulation of plasma turbulence were found to be consistent with expectations. Two experimental systems were investigated with the bispectrum. One was the periodically pulled timeseries data of a driven van der Pol oscillator (unijunction transistor circuit) which contained significant bispectral features but no real evidence of quadratic coupling. The other was plasma fluctuation data from the WVUQ Machine, where the (ioncyclotron range, sheardriven) inhomogeneous energydensity driven mode exhibited a degree of coupling to various spectral components of the lowerfrequency driftwave oscillations that was absent in the case of the currentdriven ioncyclotron mode. [Preview Abstract] 

GP16.00007: Whistler Waves Generated by an Electron Beam in Laboratory Plasma Jesus Perez, Seth Dorfman Understanding the interactions between beams of electrons and magnetized plasmas is a fundamental and practical problem. For example, energetic electrons can become trapped in the Earth's magnetic field, where they can persist for years, damaging satellites in the process. Future spacecraft may carry hardware such as a relativistic electron beam or antenna, that are able to generate a plasma wave known as the whistler mode to effectively scatter trapped electrons off the fields. Presented here is an analysis of the plasma parameters for which whistler modes are generated by a 20keV electron beam in the Large Plasma Device (LAPD) at UCLA. Properties of the observed whistler modes are also discussed. Future experiments will investigate whistler waves generated by a loop antenna. [Preview Abstract] 

GP16.00008: Linear Stability of the Slab MicroTearing Mode With a More Comprehensive Conductivity Model Joel Larakers, Richard Hazeltine, Swadesh Mahajan Gyrokinetic simulations have built a strong case that the microtearing mode (MTM) may be the principal instability responsible for the observed magnetic fluctuations in the pedestal region of an Hmode tokamak. To aid this development, we revisit and improve the semianalytic studies of the linear stability of the MTM in slab geometry, performed 40 years ago. These former studies used two simplifying approximations: (i) Electronelectron collisions are neglected (ii) The mode width does not sample the structure of the profiles. In this study, we do not make these assumptions. We begin by describing a new comprehensive conductivity model derived from kinetic theory including the full Fokker Plank collision operator. The MTM electromagnetic equations are solved with this new conductivity and the stability is studied with pedestal features in mind. [Preview Abstract] 

GP16.00009: Perpendicular electron acceleration by the lowerhybrid drift instability Jonathan Ng, LiJen Chen Electrons are typically thought be magnetized in the lowerhybrid drift instability. Recent MMS observations of the LHDI within the electron layer of guidefield reconnection, however, indicate that . intense LHDI drives nongyrotropic perpendicular electron heating. We perform 2 and 3D kinetic simulations of the LHDI in a current layer. The evolution of the LHDI leads to the formation of electron distributions with core populations as well as accelerated crescent and ring populations. We discuss the dynamics of the different electron populations and their acceleration mechanisms and relate them to the observations. [Preview Abstract] 

GP16.00010: Mitigation of runaway electrons by electrostatic waveparticle interaction Hye Lin Kang, Min Uk Lee, JeongYoung Ji, Gunsu S. Yun Runaway electron (RE) is a kinetic phenomenon that undermines the safe operation of tokamaks. We conduct a numerical study on the mitigation of REs based on a waveparticle interaction scheme. Performing 1D particleincell (PIC) simulations, we demonstrate energy reduction of REs via the inverse Landau damping. The velocity distribution of REs undergoes velocity space diffusion and damping due to the wave while the thermal electrons nearly sustain their initial distribution. Furthermore, the electron holes emerge accompanying a transition from a linear waveparticle interaction to a nonlinear phase. Finally, we discuss the nonlinear effect of the electron hole and phase mixing. [Preview Abstract] 

GP16.00011: Experimental investigation of parametric decay instability in Wendelstein 7X Andrea Tancetti, Stefan Kragh Nielsen, Jesper Rasmussen, Dmitry Moseev, Torsten Stange, Stefan Marsen, Harald Braune, Marco Zanini, Carsten Killer, Ivana Abramovic, Miklos Vecsei, Heinrich Peter Laqua Stellarators such as Wendelstein 7X (W7X) rely on microwave heating (ECRH) to reach high performance scenarios. However, if the injected power exceeds a critical threshold, nonlinear interactions, like Parametric Decay Instability (PDI), may take place, where the injected “pump” microwave decays into a pair of daughter waves. Besides reducing the efficiency of the ECRH system, daughter waves may cause severe damage to microwave diagnostics and to plasmafacing probes. Here, we investigate the properties of the anomalous signal detected via the Collective Thomson Scattering diagnostic during the last W7X experimental campaign, OP1.2(b), and explore the hypothesis of excitation due to PDI along the ECRH beams. The signal may occur as sideband peaks, symmetrically arranged around the pump frequency, or as a broadband structure, continuously stretched 500 MHz below the pump frequency. We describe the main physical quantities affecting the occurrence and the structure of the signal, and identify an experimental power threshold for the instability. We further discuss similarities with anomalous signals detected in ASDEX Upgrade that can be explained by PDI. [Preview Abstract] 
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