Nonthermal electron velocity distribution functions due to 3D kinetic magnetic reconnection for solar coronal plasma conditions
arXiv:2106.12558 · doi:10.1063/5.0061151
Abstract
Magnetic reconnection can convert magnetic energy into kinetic energy of non-thermal electron beams. Those accelerated electrons can, in turn, cause radio emission in astrophysical plasma environments such as solar flares via micro-instabilities. The properties of the electron velocity distribution functions (EVDFs) of those non-thermal beams generated by reconnection are, however, still not well understood. In particular properties that are necessary conditions for some relevant micro-instabilities. We aim at characterizing the EVDFs generated in 3D magnetic reconnection by means of fully kinetic particle-in-cell (PIC) code simulations. In particular, our goal is to identify the possible sources of free energy offered by the generated EVDFs and their dependence on the strength of the guide field. By applying a machine learning algorithm on the EVDFs, we find that: (1) electron beams with positive gradients in their 1D parallel (to the local magnetic field direction) velocity distribution functions are generated in both diffusion region and separatrices. (2) Electron beams with positive gradients in their perpendicular (to the local magnetic field direction) velocity distribution functions are observed in the diffusion region and outflow region near the reconnection midplane. In particular, perpendicular crescent-shaped EVDFs (in the perpendicular velocity space) are mainly observed in the diffusion region. (3) As the guide field strength increases, the number of locations with EVDFs featuring a perpendicular source of free energy significantly decreases. The formation of non-thermal electron beams in the field-aligned direction is mainly due to magnetized and adiabatic electrons, while in the direction perpendicular to the local magnetic field it is attributed to unmagnetized electrons.
11 figures, 1 table. This article has been published in the journal Physics of Plasmas (PoP)
References in corpus (10)
- A Review of Solar Type III Radio Bursts
- New Measure of the Dissipation Region in Collisionless Magnetic Reconnection
- Coherent Emission Mechanisms in Astrophysical Plasmas
- Why does steady-state magnetic reconnection have a maximum local rate of order 0.1?
- A Review of the 0.1 Reconnection Rate Problem
- Parallel electric fields are inefficient drivers of energetic electrons in magnetic reconnection
- Spacecraft observations and analytic theory of crescent-shaped electron distributions in asymmetric magnetic reconnection
- On the origin of the crescent-shaped distributions observed by MMS at the magnetopause
- Non-Maxwellian electron distribution functions due to self-generated turbulence in collisionless guide-field reconnection
- Characterizing magnetic reconnection regions using Gaussian mixture models on particle velocity distributions