Evolution of Magnetic Reconnection in an Electron-scale Current Sheet

Recently, a new type of magnetic reconnection, electron-only reconnection-where there is no obvious ion flow and heating-has been observed in various plasma environments. Previous kinetic simulations have shown that electron-only reconnection is a precursor of standard reconnection. In this paper, by performing a 2.5-dimensional particle-in-cell simulation, we investigate the evolution of electron-only magnetic reconnection to standard magnetic reconnection in a current sheet, whose initial width is of the electron inertial length. In the electron-only reconnection stage, electron outflow produces the electron-scale Bz pileup, and ions are slightly accelerated in the outflow direction by the Hall electric field force. As the reconnection electric field expands and Bz is piled up to the ion scale, ions start to be further accelerated inside the ion diffusion region and reflected by the Bz to the outflow direction. With Bz pileup as the bond, ions gradually transit from being accelerated by the Hall electric field to being coupled in reconnection by the Lorentz force.