Electron current layer (ECL) in the diffusion region plays an important role on energy dispassion and generation of a magnetic island during collisionless magnetic reconnection. In this study, kinetic simulations with high-resolution grids are performed to investigate the evolution of ECL during anti-parallel magnetic reconnection. It is found that ECL splits into two sublayers at the electron inertial scale, not long after the triggering of reconnection. The sublayers keep moving away from each other until reconnection rate reaches the maximum. We find the formation reason and maintaining mechanism of these sublayer structures of the ECL. When electrons flow toward the midplane, out-of-plane velocity is increased by the reconnection electric field. The deflection of magnetic field makes the out-of-plane component of velocity partly converted to the z direction. Electron flows pass through the mid-plane with super-Alfvenic speed. When they enter the other side, the increasing magnetic field makes velocity in the z direction gradually converted to the out-of-plane. Slowdown of the flows causes the density accumulation at the two sides of the mid-plane. The redistribution of electrons brings an extra pressure gradient to the ECS region, balancing the electric force and Ampere force.
Endogenous and asymmetric magnetic reconnection with associated processes of relevance to fusion burning plasmas