Magnetic Reconnection by a Self-Retreating X-Line

TL;DR

This study uses particle-in-cell simulations to investigate asymmetric collisionless magnetic reconnection, revealing a slow retreat of the X-line that does not affect the reconnection rate.

Contribution

It introduces the concept of X-line retreat in asymmetric reconnection and shows that the reconnection rate remains constant despite the retreat motion.

Findings

X-line retreats at ~0.1 times the Alfven speed.

Ion flow shows strong asymmetry and separation of stagnation point and X-line.

Reconnection rate remains unaffected by the X-line retreat.

Abstract

Particle-in-cell (PIC) simulations of collisionless magnetic reconnection are performed to study asymmetric reconnection in which an outflow is blocked by a hard wall while leaving sufficiently large room for the outflow of the opposite direction. This condition leads to a slow, roughly constant motion of the diffusion region away from the wall, the so-called `X-line retreat'. The typical retreat speed is ~0.1 times the Alfven speed. At the diffusion region, ion flow pattern shows strong asymmetry and the ion stagnation point and the X-line are not collocated. A surprise, however, is that the reconnection rate remains the same unaffected by the retreat motion.