Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session CM09: Mini-Conference: Heating and Non-Thermal Particle Acceleration during Magnetic Reconnection in Laboratory, Heliophysical and Astrophysical Plasmas IILive Streamed
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Chair: Jongsoo Yoo, Princeton Plasma Physics Laboratory; Fan Guo, Los Alamos National Laboratory Room: 206 AB |
Monday, October 17, 2022 2:00PM - 2:19PM |
CM09.00001: Electron acceleration and heating in magnetic reconnection in the shock turbulence in the Earth's bow shock Naoki Bessho, Li-jen Chen, Julia E Stawarz, Shan Wang, Michael Hesse, Lynn B Wilson, Jonathan Ng Recent space observations by NASA's Magnetospheric Multiscale (MMS) mission revealed that the turbulence in the Earth's bow shock and the magnetosheath drives magnetic reconnection and dissipates energy from magnetic field to thermal energy. Electron-only reconnection occurs in small-thickness (less than ion kinetic scale) current sheets in the shock turbulence, generating electron jets, while ions are passing through these regions. In these electron-only reconnection sites, electrons can be accelerated and heated effectively, because of large electric fields produced by the electron convection and the particle kinetic effects. Using two-dimensional particle-in-cell simulations, we investigate the shock transition region of the Earth's quasi-parallel bow shock. Performing statistical analysis of electron-only reconnection sites, we show that the reconnection electric field in electron-only reconnection is much greater than that predicted in the standard ion-coupled reconnection. Because of fast electron flows, reaching the order of the electron Alfven speed, strong electric fields are generated in reconnection regions. MMS observations in the Earth's magnetosheath show strong reconnection electric fields consistent with the prediction in electron-only reconnection. We perform particle tracing in the shock simulation to understand how electrons are energized in the shock driven reconnection. Electron temperatures in the transition region are increasing with time as many reconnection sites are generated, and the energy distribution function shows a power-law with nonthermal particles. Reconnection sites evolve dynamically, and within a fraction of ion cyclotron period, some electrons are energized very rapidly, mainly due to the perpendicular electric field, reflecting between multiple reconnection X lines or trapped in magnetic islands. We discuss the implications of reconnection for the shock electron heating and acceleration. |
Monday, October 17, 2022 2:19PM - 2:38PM |
CM09.00002: Scaling of reconnection electron heating in the low Beta and high Alfvén speed regime of Earth's magnetotail Marit Oieroset We survey 25 reconnection outflow events observed by Magnetospheric MultiScale (MMS) in the low Beta and high Alfvén speed regime of the Earth’s magnetotail to investigate the scaling of electron bulk heating produced by reconnection. The range of inflow Alfvén speeds and inflow electron Beta covered by this study is 1000 – 4000 km/s and 0.002 and 0.2 respectively, and the observed electron heating varies from a few hundred eV to ~2 keV. Thus, the study covers inflow Alfvén speeds and electron heating several orders of magnitude higher than previous scaling studies, in a regime which has applications to solar physics. We find that the amount of heating scales with the available magnetic energy per particle, similar to that found for high Beta plasmas where the inflow Alfvén speed and the amount of heating were orders of magnitude lower. In essence, these findings suggest that the scaling law for electron heating by reconnection could be universal. |
Monday, October 17, 2022 2:38PM - 2:52PM |
CM09.00003: Model for large scale electron heating applied to MMS observations in the Earth's magnetotail. Jan Egedal Magnetic reconnection is the process by which stress in the field of a magnetized plasma is reduced by a topological rearrangement of its magnetic-field lines. In the Earth’s magnetotail, reconnection energizes electrons up to hundreds of keV and solar-flare events can channel up to 50% of the magnetic energy into the electrons, resulting in superthermal populations in the MeV range. Electron energization is also fundamentally important to astrophysical applications yielding a window into the extreme environments. Using kinetic simulations it has been shown that magnetic-field aligned electric fields can be present over large spatial scales in reconnection exhausts [1,2]. The largest values of E|| are observed within double layers. The electron confinement allows sustained energization by perpendicular electric fields. The energization is a consequence of the confined electrons’ chaotic orbital motion that includes drifts aligned with the reconnection electric field. The mechanism is effective in an extended region of the reconnection exhaust allowing for the generation of superthermal electrons in large scale reconnection scenarios, including those with only a single x-line. The model is applied to new observations by the NASA’s MMS mission of large scale electron heating during reconnection in the Earth’s magnetosphere [3]. |
Monday, October 17, 2022 2:52PM - 3:11PM |
CM09.00004: High Power Reconnection Heating and Acceleration in UTokyo Tokamak Merging Experiments Yasushi Ono, Shinjiro Takeda, Haruaki Tanaka, Moe Akimitsu, Ryo Someya, Shun Kamiya, Tara Ahmadi, Kurumi Doi, Haruka Yamaguchi, Yunhan Cai, Jungkyun Kim, Hiroshi Tanabe, Shunsuke Usami, Ritoku Horiuchi, Chio Z Cheng High power reconnection heating/ acceleration experiments for direct access to the burning plasmas have been developed in TS-3, TS-4, TS-6, MAST and ST-40 merging tokamak experiments. We studied mechanisms for ion and electron heating/ acceleration of two merging tokamak plasmas by means of two imaging diagnostics: the stereo-type soft X-ray imaging for high-energy electrons and the ion Doppler imaging for ion temperature/ velocity. In the early and middle reconnection phases, we found (i) high energy (non-thermal) electrons in the downstream of reconnection which increases with reconnecting magnetic field Brec, (ii) high energy (non-thermal) electrons peaked at around X-point which increases with guide (toroidal) field Bt. The reconnection electric field is considered to accelerate electrons significantly only along the toroidal X-line. In the middle and late reconnection phases, we observed (iii) huge downstream heating of ions whose energy is as high as ~40-50% of the reconnecting (poloidal) magnetic energy. The ion heating energy is not or weekly affected by guide (toroidal) field Bt, in the tokamak operation regime: Bt/Brec>2, because the multi-blob-formation, merging, and ejection cause intermittent ion heating especially in the high Bt regime, weakening the Bt dependence of ion heating. Compression of current sheet thickness to ion gyroradius is found to be a key for realizing the fast reconnection as well as the high power ion heating consistent with the Brec2-scaling of ion heating energy. Under this condition, the ion heating energy is determined only by Brec~Bp (poloidal magnetic field), and not or weakly by Bt. This promising Brec2-scaling of ion heating energy allows us to realize the burning plasma with ion temperature Ti>10keV (under electron density ne~1.5x1019 [m-3]) by increasing Brec of merging tokamak plasmas over 0.6T. |
Monday, October 17, 2022 3:11PM - 3:30PM |
CM09.00005: Magnetic reconnection in laser-produced plasmas William R Fox, Derek B Schaeffer, Gennady Fiksel, Michael J Rosenberg, Hye-Sook Park, Kirill Lezhnin, Amitava Bhattacharjee, Daniel H Kalantar, Bruce A Remington, Dmitri A Uzdensky, Fredrick H Seguin, Chikang Li Laser-produced plasmas are a new platform for magnetic reconnection experiments which allow generation of current sheets much larger than intrinsic plasma scales and with low resistivity. We present results from experiments at the National Ignition Facility and OMEGA, where magnetic fields are generated in two expanding plumes by the Biermann battery effect. Collision of the two plasma plumes drives reconnection in a highly-elongated current sheet. The reconnection current sheet and interaction is observed with multiple diagnostics, including proton radiography to detect magnetic field structures and gated x-ray imagers to infer plasma parameters and evolution. The magnetic field measurements show that the current sheet thins down to a half-width close to the electron gyro-scale, suggesting fast reconnection supported by the electron pressure tensor. A high-energy electron spectrometer shows the enhancement in a tail of energized particles (E = 50-100 keV, >> thermal energy of 1 keV) when two plumes collide vs. single expanding plasmas. |
Monday, October 17, 2022 3:30PM - 3:49PM |
CM09.00006: Direct measurement of non-thermal electron acceleration from magnetically driven reconnection in a laboratory plasma Lan Gao, Abraham Chien, Shu Zhang, Hantao Ji, Eric G Blackman, William S Daughton, Adam J Stanier, Ari Le, Fan Guo, Russell K Follett, Hui Chen, Gennady Fiksel, Gabriel Bleotu, Robert Cauble, Sophia Chen, Alice Fazzini, Kirk A Flippo, Omar French, Dustin Froula, Julien Fuchs, Shinsuke Fujioka, Kenneth W Hill, Sallee R Klein, Carolyn C Kuranz, Philip M Nilson, Alexander M Rasmus, Ryunosuke Takizawa Magnetic reconnection is a ubiquitous astrophysical process that rapidly converts magnetic energy into some combination of plasma flow energy, thermal energy, and non-thermal energetic particles, including energetic electrons. Various reconnection acceleration mechanisms in different low-beta and collisionless environments have been proposed theoretically and studied numerically, including first- and second-order Fermi acceleration, betatron acceleration, parallel electric field acceleration along magnetic fields, and direct acceleration by the reconnection electric field. However, none of them have been heretofore confirmed experimentally, as the direct observation of non-thermal particle acceleration in laboratory experiments has been difficult due to short Debye lengths for in-situ measurements and short mean free paths for ex-situ measurements. Here we report the direct measurement of accelerated non-thermal electrons from low-beta magnetically driven reconnection in experiments using a laser-powered capacitor coil platform. We use kiloJoule lasers to drive parallel currents to reconnect MegaGauss-level magnetic fields in a quasi-axisymmetric geometry. The angular dependence of the measured electron energy spectrum and the resulting accelerated energies, supported by particle-in-cell simulations, indicate that the mechanism of direct electric field acceleration by the out-of-plane reconnection electric field is at work. Scaled energies using this mechanism show direct relevance to astrophysical observations. Our results therefore validate one of the proposed acceleration mechanisms by reconnection and establish a new approach to study reconnection particle acceleration with laboratory experiments in relevant regimes. |
Monday, October 17, 2022 3:49PM - 4:03PM |
CM09.00007: Anisotropic Electron Heating during Electron-Only Magnetic Reconnection in PHASMA Peiyun Shi, Earl Scime, Mahmud Hasan Barbhuiya, Paul A Cassak Electron-only reconnection is a variant of magnetic reconnection without significant ion involvement, which has recently been observed in the terrestrial magnetosheath and has received considerable attention due to its likely role in the energy cascade of turbulent magnetized plasmas. Different electron energization mechanisms usually favor electron acceleration along different directions and occur in different regions of reconnection. Therefore, spatially resolved electron velocity distribution function (EVDF) measurements along specific directions are required to elucidate the underlying electron energization mechanisms. In the PHAse Space MApping (PHASMA) facility, the incoherent Thomson scattering system has been upgraded to enable 3D EVDF measurements via employing two injection paths and two collection paths. Going beyond our recent work [Shi et al., Phys. Rev. Lett. 128, 025002 (2022)], both electron temperatures parallel (Te||) and perpendicular (Te⟂) to guide field have been measured during electron-only reconnection. The initial results indicate modest electron temperature anisotropies, Te|| / Te⟂ ~1.5, exist around the separatrix. One 2D spatial map of Te|| and Te⟂ will also be reported in the spirit of identifying possible electron energization mechanisms. |
Monday, October 17, 2022 4:03PM - 4:17PM |
CM09.00008: Modeling experimental reconnection with multidimensional kinetic simulations Samuel Greess, Jan Egedal, Adam J Stanier, Joseph R Olson, William S Daughton, Alexander Millet-Ayala, Ari Le, Cameron Kuchta, Paul Gradney, Cary B Forest The Terrestrial Reconnection EXperiment (TREX) as the Wisconsin Plasma Physics Laboratory (WiPPL) creates and measures different reconnection geometries in collisionless plasmas, with the aim of understanding the reconnection mechanisms of low-density space environments. Work on TREX is supplemented by kinetic simulations using VPIC, a particle-in-cell code developed at Los Alamos National Laboratory. VPIC simulations of TREX work in tandem with laboratory experiments, such that each provide feedback that shapes the designs and objectives of the other. So far, TREX data and simulations have shown agreements in layer width [1] and magnetic geometries; further work to match experimental and simulated reconnection rates and verify the occurrence of the Lower Hybrid Drift Instability are ongoing. |
Monday, October 17, 2022 4:17PM - 4:31PM |
CM09.00009: Evidence of non-thermal ions in a collisional, super-Alfvenic magnetic reconnection experiment diagnosed with Thomson scattering Lee G Suttle, Colin J Bruulsema, Jack W Halliday, Wojciech Rozmus, Danny R Russell, Vicente Valenzuela-Villaseca, Sergey V Lebedev Magnetic reconnection is a fundamental plasma physics process, which is potentially linked to the non-thermal acceleration of particles in explosive space and astrophysical events. |
Monday, October 17, 2022 4:31PM - 4:45PM |
CM09.00010: Super-Fermi acceleration in MHD plasmoid reconnection Stephen P Majeski, Hantao Ji Reconnection provides myriad mechanisms for the acceleration of plasma particles to high energies. Fermi acceleration within compressing plasmoids in particular has been used to explain energetic particle distributions throughout a range of reconnection parameters. Unfortunately, investigations of this process which focus on the individual particle acceleration are few. We present a detailed investigation of Fermi acceleration in 2D MHD anti-parallel plasmoid reconnection based on the guiding center approximation of test particle orbits. We show that accounting only for the variation in the excursion width of particle orbits around a magnetic island, energization obeys a dtε|| ~ ε||p power law where p=1+2/χ with χ typically between 3 and 3.6. Including further effects of the non-constant E?B drift allows for acceleration rates as large as p≥2, with p decreasing as plasmoid size at injection increases. As a result, plasmoid sizes are likely to be coupled to the distributions of energetic particles within. We discuss the implications this has for global energetic particle distributions in multi-island reconnection, as well as the relevance of these results to the collisionless plasmoid instability, where additional particle drifts and non-MHD effects are present. |
Monday, October 17, 2022 4:45PM - 5:00PM |
CM09.00011: Ion orbit class transitions and phase-space holes in collisionless magnetic reconnection Young Dae Yoon, Gunsu Yun The origin of anomalous ion heating in collisionless magnetic reconnection has been a longstanding problem. It was previously shown via fluid analyses, kinetic anlyses, kinetic simulations, and test-particle simulations that stochastic heating is responsible for such ion heating for up to moderate guide fields. It was also previously shown that a thinning current sheet involves particle orbit class transitions from the non-crossing to the double-well orbit class. Here we show via kinetic simulations and real-time test-particle simulations that inflowing ions during magnetic reconnection undergo orbit class changes and form phase-space holes. We then show how the orbit class changes are related to stochastic heating. |
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