Electron acceleration in the dipolarization front driven by magnetic reconnection

A large-scale two-dimensional (2-D) particle-in-cell simulation is performed in this paper to investigate electron acceleration in the dipolarization front (DF) region during magnetic reconnection. It is found that the DF is mainly driven by an ion outflow which also generates a positive potential region behind the DF. The DF propagates with an almost constant speed and gets growing, while the electrons in the DF region can be highly energized in the perpendicular direction due to betatron acceleration. For the first time, we reveal that there exists a velocity threshold; only the electrons below the threshold can be trapped by the parallel electric potential in the DF region and then energized by betatron acceleration.