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 DI02: Invited: Space Plasma PhysicsLive
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Chair: Lindsay Glesener, University of Minnesota |
Monday, November 9, 2020 3:00PM - 3:30PM Live |
DI02.00001: Observing Solar Plasma Environments with DKIST Invited Speaker: Sarah Jaeggli The Sun displays diverse plasma environments structured by magnetic fields. The largely neutral photosphere is sprinkled with $\sim$1 kG magnetic fields rooted in the underlying convection zone. Just above this magneto-acoustic shocks and rapidly expanding magnetic fields create complex and dynamic structures interspersed with quiescent and eruptive phenomena in the chromosphere. The average temperature increases through the chromosphere abruptly jumps to $> 10^6$ K in the solar corona. These different regimes are directly coupled by many processes that have been extensively studied using a combination of theory, simulations, and laboratory experiments: dynamos, waves, instabilities, and reconnection. The National Science Foundation’s Daniel K. Inouye Solar Telescope is an unprecedented new facility that will allow for measurements of the highest spatial resolution and superb signal to noise on shorter timescales than ever before. First light instruments will provide simultaneous multi-wavelength observations with spectral and polarimetric capabilities on disk and above the limb. Coupled with radiative MHD modeling, this can provide 3D diagnosis of plasma parameters (e.g. magnetic field vector, temperature) over the plasma regimes found throughout the Sun’s atmosphere. [Preview Abstract] |
Monday, November 9, 2020 3:30PM - 4:00PM Live |
DI02.00002: Some auroral arcs last all night: An unresolved theoretical challenge Invited Speaker: Sam Nogami The lifetimes of 3264 discrete auroral arcs were determined by analyzing images of discrete auroral arcs captured by all-sky imagers (ASI). These images were taken from archival data from 2007 and 2008 from three ASI cameras that are part of the THEMIS Ground-Based ASI Array during ideal viewing conditions. Arcs were tracked at one-minute intervals throughout their life cycle or until they left the camera field of view. The lifetime distribution reveals an absence of a most-probable lifetime, which constrains plausible arc generation mechanisms that might be responsible for the aurorae observed in this study to be relatively free of periodicity restrictions. The mostly featureless lifetime distribution exhibits power-law behavior with a power-law index of (-1.5 $+$/- 0.2) which emphasizes the possible importance of timescale invariant generation mechanisms. Studies dedicated to arc lifetimes are generally lacking from the literature and the differences between results obtained here and in previous small-sample-size studies of arc duration motivate the need for additional emphasis on characterizing the time-dependence of observed arcs. Further, few theoretical models of discrete arc formation make specific predictions about arc lifetime. The results of this study provide realistic time scales that can be used by modelers and theoreticians as we continue to work toward a more complete and self-consistent understanding of discrete auroral arc formation. [Preview Abstract] |
Monday, November 9, 2020 4:00PM - 4:30PM Live |
DI02.00003: Characterizing Plasmas Produced by Hypervelocity Impacts in Space Invited Speaker: Alex Fletcher Satellites experience hypervelocity impacts from meteoroids, dust, and orbital debris. A micro projectile striking a satellite at hypervelocity speeds can vaporize and ionize material forming craters and a plasma that expands rapidly into the surrounding vacuum. Various instruments on several spacecraft have measured electromagnetic signals correlated with dust impacts. Understanding the behavior of impact-produced plasmas is not only of academic interest but vital to spacecraft missions since it can damage key sensors and components. The technology available for ground-based experiments can only probe a limited range of projectile mass and velocity. Theoretically and computationally, the problem covers orders of magnitude in spatial and temporal scales as well as multi-disciplinary physics (e.g. solid mechanics, high-energy density physics, phase change and ionization, the transition between highly collisional to collisionless state, and spacecraft engineering). We discuss the behavior of plasmas produced by hypervelocity impacts. Experiments using a Van de Graaff accelerator have demonstrated that hypervelocity dust impacts can produce electromagnetic radiation that propagates away from the impact point. We simulate the process by combining an MHD/hydrocode for the impact and a particle-in-cell code for plasma expansion. The simulations are used to examine physical mechanisms that could produce the electromagnetic signals measured both on the ground and by instruments in space. We discuss a proposed in-situ experiment for characterizing plasmas generated by hypervelocity impacts. Understanding the effects of dust impacts and associated plasmas is necessary for mitigation of electrical interference and diagnosis of spacecraft malfunction. [Preview Abstract] |
Monday, November 9, 2020 4:30PM - 5:00PM Live |
DI02.00004: Large Gyroradius Effects on Gradient-Driven Plasma Instabilities Invited Speaker: Genia Vogman Instabilities in collisionless low-beta plasmas dictate cross-field transport properties. While cross-field instabilities are presently understood through the lens of reduced models like fluid and gyrokinetic descriptions, implicit assumptions of thermodynamic equilibrium or low frequency are often not applicable. Finite Larmor radius (FLR) effects, in particular, can significantly alter plasma behavior on scales that are not captured by reduced models. Kinetic simulations offer a generalized means to study plasmas far from the fluid limit; however, characterizing linear and nonlinear dynamics requires an ability to initialize and capture equilibria that satisfy the steady-state governing equations. To that end, a versatile method is developed to construct self-consistent two-species kinetic equilibria in which ion gyroradii are comparable to gradient scale lengths. By admitting customizable spatial profiles, the exact equilibria enable the targeted study of isolated physics. The method and a noise-free fourth-order Vlasov-Poisson solver are leveraged to study the linear and nonlinear dynamics of Kelvin-Helmholtz and lower-hybrid drift instabilities in nonuniform plasmas. The approach advances the state of the art by enabling comprehensive investigation of FLR-modulated instabilities in experimentally-relevant configurations. The simulations shed light on transport properties and demonstrate how FLR effects modify instability behavior. Rigorous cross-comparisons with theory and two-fluid simulations help parse the role of kinetic physics. The study has important implications for cross-field transport in pulsed power systems, the magnetosphere, Hall thrusters, and magnetically confined plasmas. These techniques expand the scope of plasma dynamics that can be captured using kinetic simulations. [Preview Abstract] |
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