Thermo-dynamic plasma expansion acceleration in asymmetric spontaneous fast magnetic reconnection

Asymmetric spontaneous fast magnetic reconnection model, in which the current sheet is initially put between two antiparallel straight magnetic field regions with different magnetic intensities, is studied by two-dimensional magnetohydrodynamic (MHD) simulations. Especially, the supersonic expansion acceleration process which has been already observed in the symmetric case is focused on. In this paper, we find that if the initial asymmetry features are weak and one side of the magnetic field regions consists of sufficiently low beta plasma, the supersonic expansion acceleration process is generated in the reconnection jet region, like the symmetric case. Hence, in such an asymmetric case, a fast shock is formed at the top of the magnetic loop.