# Electron dynamics surrounding the X-line in asymmetric magnetic reconnection

## TL;DR

This study uses particle-in-cell simulations to analyze electron behavior near the X-line in asymmetric magnetic reconnection, revealing nonadiabatic motion, crescent-shaped velocity distributions, and electron mixing regions.

## Contribution

It provides detailed insights into electron dynamics, including nonadiabatic effects and a new finite-time mixing fraction metric, in asymmetric magnetic reconnection.

## Key findings

- Electron meandering motion enhances crescent-shaped VDFs.
- Nonadiabatic electron motion occurs where magnetic curvature is comparable to Larmor radius.
- The finite-time mixing fraction identifies regions of electron mixing and energy dissipation.

## Abstract

Electron dynamics surrounding the X-line in magnetopause-type asymmetric reconnection is investigated using a two-dimensional particle-in-cell simulation. We study electron properties of three characteristic regions in the vicinity of the X-line. The fluid properties, velocity distribution functions (VDFs), and orbits are studied and cross-compared. On the magnetospheric side of the X-line, the normal electric field enhances the electron meandering motion from the magnetosheath side. The motion leads to a crescent-shaped component in the electron VDF, in agreement with recent studies. On the magnetosheath side of the X-line, the magnetic field line is so stretched in the third dimension that its curvature radius is comparable with typical electron Larmor radius. The electron motion becomes nonadiabatic, and therefore the electron idealness is no longer expected to hold. Around the middle of the outflow regions, the electron nonidealness is coincident with the region of the nonadiabatic motion. Finally, we introduce a finite-time mixing fraction (FTMF) to evaluate electron mixing. The FTMF marks the magnetospheric side of the X-line, where the nonideal energy dissipation occurs.