The Evolution of Collisionless Magnetic Reconnection from Electron Scales to Ion Scales

Abstract

It is generally accepted that collisionless magnetic reconnection is initiated on electron scales, which is mediated by electron kinetics. In this paper, by performing a two-dimensional particle-in-cell simulation, we investigate the transition of collisionless magnetic reconnection from electron scales to ion scales in a Harris current sheet with and without a guide field. The results show that after magnetic reconnection is triggered on electron scales, the electrons are first accelerated by the reconnection electric field around the X line, and then leave away along the outflow direction. In the Harris current sheet without a guide field, the electron outflow is symmetric and directed away from the X line along the center of the current sheet, while the existence of a guide field will distort the symmetry of the electron outflow. In both cases, the high-speed electron outflow is decelerated due to the existence of the magnetic field B z , then leading to the pileup of B z . With the increase of B z , the ions are accelerated by the Lorentz force in the outflow direction, and an ion outflow at about one Alfvén speed is at last formed. In this way, collisionless magnetic reconnection is transferred from the electron scales to the ion scales.

Collisionless magnetic reconnection in the magnetosphere

“…As the electrons are continuously energized and the electron current layer broadens, the ions would be coupled gradually. [97,98] Namely, this kind of "electron-only" reconnection will eventually evolves into the ion phase, corresponding to the bursty reconnection. [99] The evolution has been successfully simulated by the global PIC simulations.…”