Evolution of Magnetic Reconnection in an Electron-scale Current Sheet

Abstract 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 B z pileup, and ions are slightly accelerated in the outflow direction by the Hall electric field force. As the reconnection electric field expands and B z is piled up to the ion scale, ions start to be further accelerated inside the ion diffusion region and reflected by the B z to the outflow direction. With B z pileup as the bond, ions gradually transit from being accelerated by the Hall electric field to being coupled in reconnection by the Lorentz force.