A new Look at the Electron Diffusion Region in Asymmetric Magnetic Reconnection

TL;DR

This study investigates the electron diffusion region in asymmetric magnetic reconnection using particle-in-cell simulations, revealing complex current dissipation mechanisms and pressure effects that extend understanding beyond symmetric reconnection models.

Contribution

The paper introduces new insights into the structure and dynamics of the electron diffusion region in asymmetric reconnection, highlighting the roles of nongyrotropic pressure and convection effects.

Findings

Current dissipation linked to nongyrotropic electron pressure divergence.

Pressure terms help maintain local thermal energy against convection.

Reconnection electric field sustains current density, consistent with symmetric cases.

Abstract

A new look at the structure of the electron diffusion region in collisionless magnetic reconnection is presented. The research is based on a particle-in-cell simulation of asymmetric magnetic reconnection, which include a temperature gradient across the current layer in addition to density and magnetic field gradient. We find that none of X-point, flow stagnation point, and local current density peak coincide. Current and energy balance analyses around the flow stagnation point and current density peak show consistently that current dissipation is associated with the divergence of nongyrotropic electron pressure. Furthermore, the same pressure terms, when combined with shear-type gradients of the electron flow velocity, also serve to maintain local thermal energy against convective losses. These effects are similar to those found also in symmetric magnetic reconnection. In addition, we find here significant effects related to the convection of current, which we can relate to a generalized diamagnetic drift by the nongyrotropic pressure divergence. Therefore, only part of the pressure force serves to dissipate the current density. However, the prior conclusion that the role of the reconnection electric field is to maintain the current density, which was obtained for a symmetric system, applies here as well. Finally, we discuss related features of electron distribution function in the EDR.