The mechanisms of electron acceleration in antiparallel and guide field magnetic reconnection

Two-dimensional particle-in-cell simulations are performed to investigate electron dynamics in antiparallel and guide field (in the presence of a strong guide field) magnetic reconnection, and the mechanisms of electron acceleration are compared. In the antiparallel reconnection, the dominant acceleration occurs in the vicinity of the X line, where the magnetic field is weak. Most of these electrons come from the regions just outside of the separatrices, which move into the vicinity of the X line along the magnetic field lines. Electrons can also be nonadiabatically accelerated in the pileup region by the reconnection electric field, where the gyroradii of the electrons are comparable to the curvature radii of the magnetic field lines. Most of these electrons come from the regions inside of the separatrices, which move into the pileup region along the magnetic field lines. In the guide field reconnection, electrons are accelerated by the parallel electric field. They are firstly accelerated when moving toward the X line along the magnetic field lines, and then are further accelerated when they are funneled into the vicinity of the X line. Most of energetic electrons come from the region outside of the pair of the negative separatrices. The efficiency of such an acceleration mechanism is obviously higher than that in the antiparallel reconnection. In both the antiparallel and guide field reconnection, the mechanisms of electron acceleration favor the electrons with higher initial energy.