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 CM10: Mini-Conference: Collisionless Shocks in Laboratory and Space Plasmas IIOn Demand
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Chair: Derek Schaeffer, Princeton University Room: Room 406 |
Monday, November 8, 2021 2:00PM - 2:20PM |
CM10.00001: MMS Observations of nonlinear whistler precursor particle acceleration Lynn B Wilson, Alexandra L Brosius, Daniel J Gershman, Steven Schwartz, Hadi Madanian, Ian J Cohen, Drew L Turner, Katy Goodrich An examination reveals the disruption, deceleration, and heating of the incident solar wind ion core population by nonlinear whistler precursor waves at a high Mach number, quasi-perpendicular shock observed by the four MMS spacecraft. Interestingly, the whistler precursors cause similar disruptions to the backstreaming ions that were previously reflected by the trailing bow shock. The precursors propagate obliquely to the quasi-static magnetic field, the shock normal unit vector, and the incident bulk flow velocity vector, consistent with previous work. These large amplitude oscillations are not consistent with shock ripples. That is, the precursors are circularly polarized, not propagating along the shock surface, and have durations roughly seven times shorter than expected for shock ripples from theory. Their spatial scales range from a few 100 km down to several 10s of km, which corresponds to spatial scales spanning from from several upstream averaged ion inertial lengths to electron scales. These results suggest that whistler precursors play an important role in the conversion of bulk flow kinetic energy to other forms in the overall shock energy budget equation. |
Monday, November 8, 2021 2:20PM - 2:40PM |
CM10.00002: Fully Exploiting 3D-3V Phase Space to Understand Plasma Heating and Particle Acceleration in Collisionless Shocks Gregory G Howes, James L Juno, Collin R Brown, Colby C Haggerty, Jason M TenBarge, Damiano Caprioli, Anatoly Spitkovsky, Lynn B Wilson In weakly collisional plasmas, the physical mechanisms by which the plasma species are heated and particles are accelerated are governed by collisionless interactions between the electromagnetic fields and individual particles. The recently developed field-particle correlation technique was devised to identify and characterize the mechanisms that energize particles in the six-dimensional (3D-3V) phase space of kinetic plasmas, mechanisms underlying the fundamental plasma processes of kinetic turbulence, collisionless magnetic reconnection, and collisionless shocks. Here we present an overview of how the field-particle correlation method can be applied to gain deeper insight into the kinetic plasma processes that govern how particles are energized at collisionless shocks. Requiring only single-point measurements in space, the technique can be used to identify well-known acceleration mechanisms, such as shock drift acceleration and shock surfing acceleration. In addition, it shows promise to be able to separate the energization mediated by micro-instabilities arising in the shock transition from that due to the macroscopic shock fields. |
Monday, November 8, 2021 2:40PM - 3:00PM |
CM10.00003: Phase Space Energization in Quasi-Perpendicular and Oblique Collisionless Shocks James L Juno, Collin R Brown, Gregory G Howes, Colby C Haggerty, Jason M TenBarge, Kristopher G Klein There is growing interest in characterizing the energetics of collisionless plasmas by directly diagnosing the energy transfer between the plasma and electromagnetic fields in phase space. Unlike bulk, fluid quantities such as J ● E, diagnostics like the field-particle correlation that leverage the full 6D phase space allow us to identify how separate populations of the plasma are energized. To demonstrate the power of this phase-space analysis, we have performed a suite of 3D hybrid-kinetic quasi-perpendicular and oblique collisionless shock simulations and characterized the energization of the ions via these shocks. In particular, we can cleanly separate the energization of the different populations of ions that reflect multiple times off the shock and thus gain additional energy via the classical shock-drift acceleration mechanism. We thus identify a new phase space energization signature, sometimes referred to as shock-surfing acceleration, which can be compared with observations on the quasi-perpendicular side of Earth’s bow shock. Such comparisons will prove vital for determining the importance of shock-drift versus shock-surfing acceleration in real collisionless shocks. |
Monday, November 8, 2021 3:00PM - 3:20PM |
CM10.00004: Kinetic simulations of electron pre-energization by magnetized collisionless shocks in expanding laboratory plasmas Kirill Lezhnin, William R Fox, Derek B Schaeffer, Anatoly Spitkovsky, Jackson V Matteucci, Amitava Bhattacharjee, Kai Germaschewski Collisionless shocks are common features in space and astrophysical systems that are believed to be responsible for acceleration of charged particles up to non-thermal energies. Recent experimental capabilities and diagnostics allow detailed laboratory investigations of high-Mach-number shocks [1], which therefore can become a valuable way to understand shock dynamics in various astrophysical environments. Using 2D particle-in-cell simulations with a Coulomb binary collision operator, we demonstrate the mechanism for generation of energetic electrons and experimental requirements for detecting this process in the laboratory high-Mach-number collisionless shocks at parameters that may be achieved in near future experiments [2]. |
Monday, November 8, 2021 3:20PM - 3:40PM |
CM10.00005: Magnetic Reflection of Heavy Ions from High Mach Number Quasi-Perpendicular Shocks: MMS Observations Hadi Madanian Strong shocks in collisionless plasmas, such as supernovae shocks and shocks driven by coronal mass ejections, are known to be a primary source of energetic particles. In this talk, I will discuss recent observations of nonstationarity and ion acceleration processes at high Mach number quasi-perpendicular shocks. Results are based on in-situ measurements of the Magnetospheric Multiscale (MMS) spacecraft at Earth's bow shock which in rare instances has shock parameters close to those predicted at supernova remnants. High time resolution and multipoint measurements enable us to characterize ion and electron scale kinetic effects and to distinguish spatial variations from time-dependent effects in the shock layer and upstream perturbations. |
Monday, November 8, 2021 3:40PM - 4:00PM |
CM10.00006: Kinetic Simulations of the Behavior of Pickup Ions in the Vicinity of a Collisionless Shock Vadim S Roytershteyn, Patrick F Kilian, Michael Gedalin, Nikolai Pogorelov Charge exchange between outflowing solar wind and neutrals of interstellar origin becomes increasingly important at large heliospheric distances. Consequently, the plasma upstream of the heliospheric termination shock (TS) is characterized by the presence of a distinct population of superthermal pickup ions with shell-like distributions (PUIs). It is well-appreciated that PUIs significantly affect the TS structure and gain the majority of the kinetic energy lost by the solar wind upon the shock transition. Quantitative understanding of the behavior of PUIs at the TS is important for many applications, notably to be able to model PUIs in global heliospheric models that rely on MHD framework and thus cannot directly describe the kinetic behavior of PUIs at the TS. In this contribution, we discuss results from fully kinetic and hybrid (kinetic ions + fluid electrons) simulations targeting the question of how PUIs are energized upon transition through the TS. In particular: i) fully kinetic and hybrid simulations of the immediate vicinity of the shock transition are cross-validated and their results are compared to predictions of a particle-tracing model, demonstrating good agreement; validated hybrid simulations are used to study ii) the relaxation of anisotropic distributions generated upon shock transition and iii) particle reflection from the shock and the generation of upstream perturbations by back-streaming PUIs. |
Monday, November 8, 2021 4:00PM - 4:20PM |
CM10.00007: Modeling Solar Wind Interaction with the Local Interstellar Medium using Kinetically-Derived Rankine-Hugoniot Conditions for Pickup Ions Nikolai Pogorelov, Michael Gedalin, Vadim S Roytershteyn, Ratan Kumar Bera, Federico Fraternale, William P Smith, Ming Zhang Non-thermal, pickup ions (PUI) are born when interstellar neutral atoms experience charge exchange charge with the solar wind (SW) ions. PUIs created in the supersonic SW quickly acquire the velocity of ambient ions, but are never in equilibrium with them. The PUI pressure soon becomes dominant as compared with the thermal SW ion pressure and magnetic pressure. While there were several attempts to model the SW interaction with the local interstellar medium (LISM) with PUIs treated on different levels of sophistication, they are not entirely satisfactory because of the very approximate description of their crossing of the (collisionless, quasi-perpendicular) heliospheric termination shock (TS). The challenging aspect of this process is that the PUI distribution function becomes anisotropic in the shock vicinity. We have used test-particle and full PIC simulations to describe such boundary conditions and parameterize them using the shock angle and magnetic compression across the shock. This allows us to model the 3-D SW-LISM interaction and compare our new results with those obtained with the traditional approaches that ignore the kinetics of ions crossing the TS. Simulations are performed using our Multi-Scale Fluid-Kinetic Simulation Suite (MS-FLUKSS), which is capable of modeling PUIs as an ion component separate from the thermal SW plasma. This is done by treating PUIs as a separate fluid, the distribution function of which is isotropic away from the TS. With our new boundary conditions, we are able to improve the accuracy of simulations and make them physically consistent. Our new results are compared with those obtained with the traditional approaches that ignore the ion kinetics near the TS. |
Monday, November 8, 2021 4:20PM - 4:40PM |
CM10.00008: Proton Distribution in the Heliosheath: From Particle Acceleration at the Termination Shock to Energetic Neutral Atom Observation near Earth Eric Zirnstein, Maher Dayeh, Rahul Kumar, Jacob Heerikhuisen, Riddhi Bandyopadhyay, David J McComas, Pawel Swaczyna The Interstellar Boundary Explorer (IBEX) measures energetic neutral atom (ENA) emissions from the outer heliosphere in the energy range ~0.5-6 keV. ENAs are produced by charge exchange between energetic pickup ions (PUIs) in the heliosheath and cold neutral atoms from the local interstellar medium. PUIs are preferentially accelerated at the heliospheric termination shock (HTS) before propagating through the heliosheath. Thus, IBEX ENA measurements reveal line-of-sight averaged proton spectra over the sky and their acceleration mechanism. |
Monday, November 8, 2021 4:40PM - 5:00PM |
CM10.00009: Stochastic Electron Acceleration in High-Mach-Number Collision-less Shocks Yosuke Matsumoto Elucidating acceleration mechanisms of charged particles have been of great interests in laboratory, space, and astrophysical plasmas. Among other mechanisms, a collision-less shock is thought as an efficient particle accelerator. The diffusive shock acceleration (DSA) theory has provided a solution to observational evidences for efficient accelerations at collision-less shocks, as it predicts a power-law energy spectrum of particles having a spectral index that is close to the values suggested by multi-wavelength observations. As the DSA theory presumes pre-existing mildly energetic particles, pre-acceleration mechanisms are required to provide a seed population for DSA, particularly for electrons. The connection between pre-acceleration and DSA remains a critical issue in shock acceleration theory. |
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