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 JO05: Fundamental Plasmas: Waves and InstabilitiesLive

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Chair: Mark Koepke, West Virginia University 
Tuesday, November 10, 2020 2:00PM  2:12PM Live 
JO05.00001: Formation and Consequences of Ion Acoustic Double Layers Alexander Vazsonyi, Kentaro Hara, Iain Boyd Nonmonotonic double layers, coherent plasma structures which sustain a potential gradient through an asymmetric potential well (or peak), may develop in a plasma subject to currentcarrying instabilities. These structures are known to generate electron phase space holes, signifying a major perturbation to electron transport. In this work, 1D1V VlasovPoisson simulations are used to study a plasma subject to the ion acoustic instability. Upon saturation of this instability, a secondary growth of small wavenumber ion acoustic waves occurs which ultimately results in nonmonotonic double layer formation. Electron reflection off and acceleration through such a double layer generates a twostream instability, creating largeamplitude (with respect to the already present ion acoustic waves) plasma waves associated with electron holes. The magnitude of the double layer, found to scale inversely with ion mass, dictates the amount of electron reflection and thus the phase speed of the resulting electron plasma waves. [Preview Abstract] 
Tuesday, November 10, 2020 2:12PM  2:24PM Live 
JO05.00002: Interaction between a soliton and a double layer in a traveling magnetic field system Harihara Kumar, Masayuki Takahashi, Chinami Kato, Naofumi Ohnishi The case of a magnetic pulse traveling through a plasma is studied theoretically. Double layer (DL) and solitons were observed in this system before and it's known that certain DLs decay by emitting solitons$^{\mathrm{1}}$. However, the exact trigger mechanism causing this DLsoliton transition is not understood yet. Theoretically, this transition can be treated as a DLsoliton interaction. The soliton and DL KdV equations for the traveling pulse case is derived using the Reductive Perturbation Method (RPM) by considering trapped and free electrons and free ions. RPM is used to reduce nonlinear PDEs using asymptotic expansions. This means the interaction term between the 1$^{\mathrm{st}}$ order soliton and the 2$^{\mathrm{nd}}$ order DL is usually lost and the system of equations is unclosed. In this study, the closure is achieved by assuming an ion density distribution in the DL and backsubstituting the DL parameters into the soliton system as a higher order asymptote. The interaction term thus found is directly proportional to the trapped electron density. A higher trapped electron density means an increased DLsoliton interaction and a decreased chance of DL decay. The interaction is also solitary in nature. $^{\mathrm{1}}$Ikezi H, Taylor R J and Baker D R, 1970, Formation and Interaction of IonAcoustic Solitons, Phy. Rev. Lett., 25, pp. 11  14. [Preview Abstract] 
Tuesday, November 10, 2020 2:24PM  2:36PM Live 
JO05.00003: Free energy available to microinstabilities in the solar wind Emily Lichko, Kristopher Klein In the solar wind we observe that there is a significant amount of power in highfrequency waves. In the current picture of weaklycollisional plasma turbulence, energy can be transferred to these waves through microinstabilities generated by nonequilibrium features in the velocity distribution functions of the constituent particles. However, it is an open question how much energy in these features is truly available to drive these waves and eventually heat the plasma. In this work we develop an ansatz to quantify the amount of free energy available to microinstabilities that can actually go into heating the plasma relative to other dissipation mechanisms. We apply this metric to a number of electrostatic test cases, and plan to apply the metric to Parker Solar Probe observations of electron distributions and Langmuir waves. Ultimately this metric will be applied to simulations of electromagnetic instabilities as well, and modified to account for the role of multiple types of microinstabilities and sources of free energy. [Preview Abstract] 
Tuesday, November 10, 2020 2:36PM  2:48PM Live 
JO05.00004: Topological Waves in Plasmas and Analogs to Topological Insulators Jeffrey Parker, Brad Marston, Steve Tobias, Ziyan Zhu A topological understanding of matter is not only deepening our knowledge of physics, but also leading to novel practical devices and applications. Nontrivial topology in bulk matter has been linked with the existence of topologically protected interfacial states. While these concepts were originally developed in electronic structures and photonic systems, recent advances have demonstrated that continuum fluid systems can support topological waves. We extend these ideas to plasmas and show that a gaseous plasmon polariton (GPP), an electromagnetic surface wave existing at the boundary of magnetized plasma and vacuum, has a topological origin that arises from the nontrivial topology of magnetized plasma. Moreover, we show that the GPP may be found within a gapped spectrum in presentday laboratory devices, suggesting that platforms are currently available for experimental investigation of topological wave physics in plasmas. Experiments to confirm the existence of this wave would open a new frontier in the exploration of the physics of topological waves in plasmas. \\ \\J. B. Parker, J. B. Marston, S. M. Tobias, Z. Zhu, Phys. Rev. Lett. 124, 195001 (2020) [Preview Abstract] 
Tuesday, November 10, 2020 2:48PM  3:00PM Live 
JO05.00005: Surface Signatures of Subsurface Magnetic Fields: Written on the Stellar Atmospheric Waves Bindesh Tripathi, Dhrubaditya Mitra Internal dynamogenerated magnetic fields in the stars are inaccessible to direct observations, thus deterring our understanding of their origin and evolution in time. A tool that has proved very useful in analyzing the stellar interiors, called asteroseismology, however, has not yet been able to provide details of internal stellar magnetic fields. Here, we investigate the signatures of subsurface magnetic fields in the dispersion relations of acoustic waves (trapped near the stellar surface). We first begin with an isothermal, stratified atmosphere, permeated by a nonuniform (exponential function of the vertical coordinate) horizontal magnetic field (Ref: \underline {arXiv:1812.06947}). We solve the problem exactly. Next we consider a more realistic polytropic atmosphere. We calculate the dispersion relation numerically and perturbatively. We show that the presence of a horizontal magnetic field breaks the symmetry of rings of constant frequencies over the horizontal wavenumbers. Such asymmetry arising from the magnetic fields eludes the standard helioseismology with its present resolution. Our results hint that internal stellar magnetic fields might be possible to infer based upon stellar surface oscillations. [Preview Abstract] 
Tuesday, November 10, 2020 3:00PM  3:24PM Live 
JO05.00006: Coherent PitchAngle Interaction between Whistler Waves and a Distribution of Energetic Particles (PhD Oral24) Young Dae Yoon, Paul M. Bellan How coherent whistler waves interact with energetic particles is a crucial question in magnetospheric plasma physics, as well as in the context of runaway electrons in fusion devices. A recent study \footnote{P. M. Bellan, Phys. Plasmas, 20, 042117} showed that an exact rearrangement of the relativistic particle equation of motion under a circularlypolarized wave leads to an equation describing the motion of the “frequency mismatch” parameter $\xi$ under a pseudopotential $\psi$. When the shape of the pseudopotential is twovalleyed and the particle has enough pseudoenergy to undergo twovalley motion, $\xi$ and the pitchangle changes greatly. In the present study, the analysis is extended to a distribution of particles. A general condition for twovalley motion is first derived. It is then shown via singleparticle simulations that particles which satisfy the twovalley condition indeed undergo large pitchangle changes. Then, the fraction of twovalley particles are calculated assuming that the particle distribution is MaxwellJ\"{u}ttner, which is the relativistic generalization of the MaxwellBoltzmann distribution. For magnetospheric parameters, at least 15\% of the particles undergo twovalley motion, and this fraction is verified by singleparticle simulations [Preview Abstract] 
Tuesday, November 10, 2020 3:24PM  3:36PM Live 
JO05.00007: Reconciling Landau and van KampenCase: the Suppression of Decaying Discrete Modes Frank Lee, Bradley Shadwick The solution by Landau of the onedimensional linear Vlasov equation, which describes a collisionless plasma, shifts and deforms the Bromwich contour around the poles of the analyticallycontinued dielectric function. For an unstable equilibrium with growing and decaying normal modes, this procedure results in only the growing modes contributing. However, the van KampenCase solution shows that the eigenfunctions of the decaying discrete modes always accompany those of the growing discrete modes, and thus a contradiction seems to arise, since both Landau and van KampenCase give valid solutions. In order to reconcile the two seemingly different answers, we present a solution that is equivalent to both and show that the decaying discrete modes do not actually exist; a part of the van Kampen continuum seems to always conspire to exactly cancel the decaying discrete modes. Our solution evaluates the Bromwich integral using properties of Cauchytype integrals instead of deforming the contour, avoiding the analytic continuation from the Landau method. It also avoids the complicated principal value integrals from the van KampenCase method; only a straightforward Laurent series expansion is required. [Preview Abstract] 
Tuesday, November 10, 2020 3:36PM  4:00PM Live 
JO05.00008: MomentumExchange Current Drive, Alpha Channeling, and Rotation (PhD Oral24) Ian Ochs, Nathaniel Fisch The electric field associated with a planar electrostatic wave has no average momentum, and thus as the waves damp, the momentum of the plasma has to be conserved. We examine various implications of this momentum conservation. In the planar problem, we show how wavemediated momentum exchange between nonresonant and resonant particles can drive net currents in spite of the constraint [1]. This momentumexchange current drive can provide a possible magnetogenesis mechanism in astrophysical settings. Adding spatial wave structure, important for application to steadystate laboratory devices, introduces new momentum terms. We discuss the implications of our results for wavemediated perpendicular momentum transport in magnetized plasmas with hot ion gradients, drawing analogies with collisional momentum transport in rotating ExB plasmas [24]. \\ 1) I.E. Ochs and N.J. Fisch, Physics of Plasmas 27(6), 062109 (2020).\\ 2) E.J. Kolmes, I.E. Ochs, M.E. Mlodik, J.M. Rax, R. Gueroult, and N.J. Fisch, Physics of Plasmas 26(8), 082309 (2020).\\ 3) I. E. Ochs and N. J. Fisch, Physical Review Letters 121, 235002 (2018).\\ 4) I. E. Ochs and N. J. Fisch, Physics of Plasmas 25(12), 122306 (2018). [Preview Abstract] 
Tuesday, November 10, 2020 4:00PM  4:12PM Live 
JO05.00009: Radio and Plasma Wave Generation by an Electron Beam in a Laboratory Plasma S Dorfman, V Roytershteyn, C Cattell, C Colpitts, GL Delzanno, Q Marksteiner Interaction between relativistic electron beams and magnetized plasma is a fundamental and practical problem relevant to many challenging issues in space physics and astrophysics. We present results from a 20~keV beam experiment on the Large Plasma Device (LAPD) at UCLA motivated by the problem of how naturally occurring electron beams may produce type II/III solar radio emissions as well as recent proposals to place compact highenergy electron beam sources on future spacecraft. These spacecraftborne beams may be used to map magnetic field lines in the Earth's magnetosphere or to generate waves for radiation belt remediation. In the LAPD experiments, electromagnetic emission between the plasma and upper hybrid frequencies is observed by both insitu probes and by an antenna outside of the plasma. The parallel phase speed of the excited waves is measured to be consistent with generation via a resonance process, while estimates of the radiated power are consistent with incoherent Cherenkov emission. Kinetic modeling suggests that the apparent absence of strong instabilities is due to velocity dispersion imposed by the beam injection conditions. Signatures of nonlinear interactions between fluctuations above the plasma frequency and observed whistler modes are also observed. [Preview Abstract] 
Tuesday, November 10, 2020 4:12PM  4:24PM Live 
JO05.00010: Recent Progress of High Harmonics Fast Wave (HHFW) Project on LAPD* Xiaokang Yang, Tim DeHaase, Troy Carter, Steve Vincena, Richard Goulding, Bart Van Compernolle, Ian Allfrey, Jon Schroeder, Andy Sibley, Ping Feng, Francesco Ceccherini, Laura Galeotti, Cornwall Lau, Nicola Bertelli, Masa Ono, Syun'ichi Shiraiwa To conduct the proofofprinciple experiments of high harmonic fast wave (HHFW) coupling and propagation in high beta FRC plasma, a phasedarray RF antenna has been designed, built, and installed on the LArge Plasma Device (LAPD). The first experimental campaign of fast wave propagation at low power operation has shown promising results that fast waves can couple and propagate into the plasma core at all antenna phases, even when the antenna is fully retracted close to the wall, and no slow wave excitation has been observed. The magnetic field components of HHFWs in both the near and far fields were measured by Bdot probes, and these measuremental results are used to benchmark the simulation results with the PetraM full wave code. Meanwhile, a few sets of impedance matching network, decoupler, and antenna phase and impedance measurement diagnostics are currently under construction; this hardware will be deployed on LAPD soon for a new RF campaign, and its experimental results will be presented. *The experiments were performed at UCLA's Basic Plasma Science Facility, which is a collaborative research facility supported by the US DoE, and the NSF. [Preview Abstract] 
Tuesday, November 10, 2020 4:24PM  4:36PM Live 
JO05.00011: Numerical Simulation of Rotating Spokes on a Partially Magnetized ExB Magnetron Sputtering Device Masayuki Takahashi, JeanPierre Boeuf ExB plasma is sustained on a partially magnetized plasma devices such as Hall thruster and magnetron sputtering because electron heating occurs and electronimpact ionization is maintained. A rotating spoke structure was experimentally and numerically captured on ExB device, and mechanism of spoke rotation was discussed. The past experiment for magnetron sputtering device indicated that the direction of spoke propagation is changed depending on the applied voltage, and ExB drift motion of the rotating spoke was captured. However, a detailed mechanism on ExB motion of spokes was not revealed and a propagation velocity of ExB spoke was not characterized. In this study, we conducted a twodimensional particleincell (PIC) simulation with Monte Carlo collision (MCC) to capture dynamics of ExB spoke on the magnetron sputtering devices. Our PICMCC simulation described that the electron around the double layer is heated by a crossfield motion of gradient B drift. This high temperature electron induces the electronimpact ionization at the double layer, which causes the spoke propagation to the ExB direction. Our modeling finally concluded that the propagation velocity of rotating spokes can be characterized by the electron diffusion coefficient and ionization frequency. [Preview Abstract] 
Tuesday, November 10, 2020 4:36PM  4:48PM 
JO05.00012: Shear Flow‐Interchange Instability in Nightside Magnetotail Observed as "Auroral Beads” at Substorm Onset Wendell Horton, J. Derr, R. Wolf, B. Breizman Low‐frequency shear flow‐interchange waves transmit sheared zonal flows along magnetic flux tubes toward the ionosphere from the near‐Earth nightside plasma sheet create the "auroral beads” observed in Canada and Alaska observed as the geomagnetic substorm onset. A set of nonlinear pde’s is derived and solved to model the growth and saturation of the auroral beads. The relation with the Kalmoni model (2015, https://doi.org/10.1002/2015JA021470) for shear flow‐ballooning instability is explained. The shear flow‐interchange instability appears to be responsible for substorm onset. The growth starts in the midnight region of the nightside magnetotail producing in the nonlinear stage the auroral beads characteristic of geomagnetic substorm onset. [Preview Abstract] 
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