 Award ID(s):
 1842638
 NSFPAR ID:
 10417721
 Date Published:
 Journal Name:
 Physics of Plasmas
 Volume:
 29
 Issue:
 5
 ISSN:
 1070664X
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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Magnetic reconnection plays an important role in the release of magnetic energy and consequent energization of particles in collisionless plasmas. Energy transfer in collisionless magnetic reconnection is inherently a twostep process: reversible, collisionless energization of particles by the electric field, followed by collisional thermalization of that energy, leading to irreversible plasma heating. Gyrokinetic numerical simulations are used to explore the first step of electron energization, and we generate the first examples of fieldparticle correlation (FPC) signatures of electron energization in 2D strongguidefield collisionless magnetic reconnection. We determine these velocity space signatures at the xpoint and in the exhaust, the regions of the reconnection geometry in which the electron energization primarily occurs. Modeling of these velocityspace signatures shows that, in the strongguidefield limit, the energization of electrons occurs through bulk acceleration of the outofplane electron flow by parallel electric field that drives the reconnection, a nonresonant mechanism of energization. We explore the variation of these velocityspace signatures over the plasma beta range 0.01 < beta_i < 1. Our analysis goes beyond the fluid picture of the plasma dynamics and exploits the kinetic features of electron energization in the exhaust region to propose a singlepoint diagnostic which can potentially identify a reconnection exhaust region using spacecraft observations.more » « less

Abstract Using 3D particleincell simulation, we characterize energy conversion, as a function of guide magnetic field, in a thin current sheet in semirelativistic plasma, with relativistic electrons and subrelativistic protons. There, magnetic reconnection, the driftkink instability (DKI), and the fluxrope kink instability all compete and interact in their nonlinear stages to convert magnetic energy to plasma energy. We compare fully 3D simulations with 2D in two different planes to isolate reconnection and DKI effects. In zero guide field, these processes yield distinct energy conversion signatures: ions gain more energy than electrons in 2D
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Particle energization due to magnetic reconnection is an important unsolved problem for myriad space and astrophysical plasmas. Electron energization in magnetic reconnection has traditionally been examined from a particle, or Lagrangian, perspective using particleincell (PIC) simulations. Guidingcenter analyses of ensembles of PIC particles have suggested that Fermi (curvature drift) acceleration and direct acceleration via the reconnection electric field are the primary electron energization mechanisms. However, both PIC guidingcenter ensemble analyses and spacecraft observations are performed in an Eulerian perspective. For this work, we employ the continuum Vlasov–Maxwell solver within the Gkeyll simulation framework to reexamine electron energization from a kinetic continuum, Eulerian, perspective. We separately examine the contribution of each drift energization component to determine the dominant electron energization mechanisms in a moderate guidefield Gkeyll reconnection simulation. In the Eulerian perspective, we find that the diamagnetic and agyrotropic drifts are the primary electron energization mechanisms away from the reconnection xpoint, where direct acceleration dominates. We compare the Eulerian (Vlasov Gkeyll) results with the wisdom gained from Lagrangian (PIC) analyses.more » « less

Abstract We perform a 2.5dimensional particleincell simulation of a quasiparallel shock, using parameters for the Earth’s bow shock, to examine electron acceleration and heating due to magnetic reconnection. The shock transition region evolves from the ioncoupled reconnection dominant stage to the electrononly reconnection dominant stage, as time elapses. The electron temperature enhances locally in each reconnection site, and ionscale magnetic islands generated by ioncoupled reconnection show the most significant enhancement of the electron temperature. The electron energy spectrum shows a power law, with a powerlaw index around 6. We perform electron trajectory tracing to understand how they are energized. Some electrons interact with multiple electrononly reconnection sties, and Fermi acceleration occurs during multiple reflections. Electrons trapped in ionscale magnetic islands can be accelerated in another mechanism. Islands move in the shock transition region, and electrons can obtain larger energy from the inplane electric field than the electric potential in those islands. These newly found energization mechanisms in magnetic islands in the shock can accelerate electrons to energies larger than the achievable energies by the conventional energization due to the parallel electric field and shock drift acceleration. This study based on the selected particle analysis indicates that the maximum energy in the nonthermal electrons is achieved through acceleration in ionscale islands, and electrononly reconnection accounts for no more than half of the maximum energy, as the lifetime of subionscale islands produced by electrononly reconnection is several times shorter than that of ionscale islands.

null (Ed.)Using the field–particle correlation technique, we examine the particle energization in a threedimensional (one spatial dimension and two velocity dimensions; 1D2V) continuum Vlasov–Maxwell simulation of a perpendicular magnetized collisionless shock. The combination of the field–particle correlation technique with the highfidelity representation of the particle distribution function provided by a direct discretization of the Vlasov equation allows us to ascertain the details of the exchange of energy between the electromagnetic fields and the particles in phase space. We identify the velocityspace signatures of shockdrift acceleration of the ions and adiabatic heating of the electrons arising from the perpendicular collisionless shock by constructing a simplified model with the minimum ingredients necessary to produce the observed energization signatures in the selfconsistent Vlasov–Maxwell simulation. We are thus able to completely characterize the energy transfer in the perpendicular collisionless shock considered here and provide predictions for the application of the field–particle correlation technique to spacecraft measurements of collisionless shocks.more » « less