Decoupling of Electron and Ion Dynamics in Driven Magnetic Reconnection in Collisionless Plasmas

The purpose of the paper is to describe the decoupling processes of electron and ion dynamics in the reconnection layer (current sheet and separatrix regions) and how the in-plane electrostatic electric field and the parallel electric field are produced. During driven magnetic reconnection of oppositely directed magnetic field lines, both ions and electrons drift together with the merging field lines toward the neutral sheet where the magnetic field lines reconnect. Because the electron outflow velocity is much larger than the ion outflow velocity, a pair of currents flow inward toward the magnetic reconnection region and produce the quadrupole out-of-plane magnetic field concentrated around the separatrix regions. The parallel electric field is produced by the driving electric field and the quadrupole magnetic field and points toward the downstream direction. The parallel electric field accelerates electrons toward the reconnection region direction but ions move slowly across the separatrix field lines, which causes decoupling of the electron and ion flow dynamics around the separatrix regions to generate charge separation and produce electrostatic electric field pointing across the separatrix field lines toward the mid-plane direction. Around the magnetic reconnection region where the magnetic fields become weakened and reversed, the particle orbits perpendicular to the field lines become meandering. Because the ion meandering region width is much larger than the electron meandering region width, charge separation is produced inside the ion meandering region and produces a pair of strong bipolar in-plane electrostatic electric fields pointing toward the mid-plane direction. With the production of quadrupole magnetic field, the parallel electric field and the electrostatic electric field, particle dynamics and acceleration/heating can be understood. (C) 2016 The Japan Society of Plasma Science and Nuclear Fusion Research