Particle Acceleration by Magnetic Reconnection in Geospace

Abstract

Particles are accelerated to very high, non-thermal energies during explosive energy-release phenomena in space, solar, and astrophysical plasma environments. While it has been established that magnetic reconnection plays an important role in the dynamics of Earth’s magnetosphere, it remains unclear how magnetic reconnection can further explain particle acceleration to non-thermal energies. Here we review recent progress in our understanding of particle acceleration by magnetic reconnection in Earth’s magnetosphere. With improved resolutions, recent spacecraft missions have enabled detailed studies of particle acceleration at various structures such as the diffusion region, separatrix, jets, magnetic islands (flux ropes), and dipolarization front. With the guiding-center approximation of particle motion, many studies have discussed the relative importance of the parallel electric field as well as the Fermi and betatron effects. However, in order to fully understand the particle acceleration mechanism and further compare with particle acceleration in solar and astrophysical plasma environments, there is a need for further investigation of, for example, energy partition and the precise role of turbulence.

Laboratory Study of Collisionless Magnetic Reconnection

“…Recent progress in directly detecting electrons accelerated by the reconnection electric field (Chien et al 2023) and non-thermal electrons by Thomson scattering (Shi et al 2022) is an encouraging sign that more results are coming. The predicted scaling of electron heating and acceleration by the parallel electric field with regard to upstream β (Le et al 2016) is in agreement with certain spacecraft observations (Oka et al 2023), but its laboratory study sensitively depends on plasma collisionality (Le et al 2015). High Lundquist number regimes offered by the upgraded TREX (Olson et al 2016) and the upcoming Facility for Laboratory Reconnection Experiments or FLARE (Ji et al 2018 will allow first laboratory accesses to the collisionless regimes required to study this important issue of collisionless reconnection.…”

Observation of Energetic Electron Near the Electron Diffusion Region of Magnetic Reconnection

“…Magnetic reconnection is one of the crucial mechanisms for the production of these energetic electrons. Previous studies found that a number of electrons can be directly accelerated to very high energy during magnetic reconnection (S. Y. Huang et al., 2012; Lin & Hudson, 1971; Q. Lu et al., 2022; Øieroset et al., 2001; Oka et al., 2023; Su et al., 2013; R. Wang et al., 2016; R. Wang, Lu, Li, et al., 2010). For example, energetic electrons of up to hundreds of keV have been detected in the vicinity of the reconnection region of the Earth's magnetosphere (L. J. Chen et al., 2008; H. S. Fu et al., 2013; Li et al., 2022; R. Wang, Lu, Li, et al., 2010).…”

“…Previous studies found that a number of electrons can be directly accelerated to very high energy during magnetic reconnection (S. Y. Huang et al, 2012;Lin & Hudson, 1971;Øieroset et al, 2001;Oka et al, 2023;Su et al, 2013;R. Wang et al, 2016;R.…”