Macro-particle simulations of collisionless magnetic reconnection

The basic process of collisionless reconnection is studied in terms of coalescence of two flux bundles using an implicit particle simulation of two-dimensions. As the toroidal electric field is generated by magnetic induction, an elongated current sheet whose width is a few electron skin depths is formed. Sub-Alfvénic plasma outflow off the reconnection region is generated in the poloidal plane which spreads within the dual fans originating at the X-point. Significant toroidal acceleration and streaming of the electrons without direct thermalization is observed in the current sheet. The electron parallel transport is proved to enhance the reconnection rate by comparing the implicit and hybrid-particle simulations; in the latter the electrons are spatially frozen to the ions. The reconnection rate is insensitive to finite Larmor radii of the ions in the regime where the magnetic flux merges constantly in time. The simulation results support that the collisionless reconnection is mediated by the electron inertia.