Anisotropic Heating and Parallel Heat Flux in Electron-only Magnetic Reconnection with Intense Guide Fields

TL;DR

This study uses kinetic simulations to explore how intense guide magnetic fields influence electron heating, anisotropy, and heat flux in electron-only magnetic reconnection, revealing structural transitions and non-Maxwellian electron behaviors.

Contribution

It provides new insights into the effects of strong guide fields on electron dynamics and temperature structures in electron-only reconnection through detailed kinetic simulations.

Findings

Guide fields cause narrower quadrupolar magnetic structures.

Electron velocities exceed ion velocities significantly.

Strong parallel electron heat flux observed with increasing guide fields.

Abstract

Electron-only reconnection is a process recently observed in the Earth's magnetosheath, where magnetic reconnection occurs at electron kinetic scales with only electrons involved. Electron-only reconnection is likely to have a significant impact on the energy conversion and dissipation of turbulence cascades at kinetic scales. This paper investigates electron-only reconnection under different intensities of strong guide fields via two-dimensional fully kinetic Particle-in-Cell (PIC) simulations, focusing on electron heating. The simulations are initialized with a force-free current sheet equilibrium under various intensities of strong guide fields. The quadrupolar structures of the out-of-plane magnetic field and asymmetric structures of density are found to become narrower in space as the guide field increases. Electron velocities are considerably larger than ion velocities, and the motion of both species is notably affected by the strength of guide fields. Similarly to previous experiments studies, electron temperature anisotropy along separatrices is observed, which is found to be mainly caused by the variations of parallel temperature. Both regions of anisotropy and parallel temperature increase/decrease along separatrices become thinner with increasing guide fields. Besides, we find a transition from a quadrupolar to a six-polar to an eight-polar structure in temperature anisotropy and parallel temperature as the guide field intensifies. Non-Maxwellian electron velocity distribution functions (EVDFs) at different locations in the three simulations are observed. Our results show that parallel electron velocity varies notably with different guide field intensities and strong parallel electron heat flux is observed.