Orientation of x-lines in asymmetric magnetic reconnection - mass ratio dependency

TL;DR

This study uses kinetic simulations to analyze how the orientation of x-lines in asymmetric magnetic reconnection depends on ion-to-electron mass ratio, revealing a tendency to bisect the magnetic shear angle at large mass ratios.

Contribution

It demonstrates that x-line orientation tends to bisect the magnetic shear angle in large mass ratio limits and links deviations at lower ratios to tearing instability physics.

Findings

X-line bisects magnetic shear angle at high mass ratios

Orientation can be predicted by maximizing reconnection electric field in 2D scans

Deviations at low mass ratios explained by tearing instability physics

Abstract

Using fully kinetic simulations, we study the x-line orientation of magnetic reconnection in an asymmetric configuration. A spatially localized perturbation is employed to induce a single x-line, that has sufficient freedom to choose its orientation in three-dimensional systems. The effect of ion to electron mass ratio is investigated, and the x-line appears to bisect the magnetic shear angle across the current sheet in the large mass ratio limit. The orientation can generally be deduced by scanning through corresponding 2D simulations to find the reconnection plane that maximizes the peak reconnection electric field. The deviation from the bisection angle in the lower mass ratio limit can be explained by the physics of tearing instability.