Suprathermal particle energization in dipolarization fronts: Particle-in-cell simulations

Within dipolarization fronts (DFs) in the Earth's magnetotail, significant magnetic energy is converted to plasma energy, and a significant portion of the electrons and ions therein are accelerated to suprathermal energies. The mechanism that produces these suprathermal particles while simultaneously reducing magnetic field energy is poorly understood, however. We use two-dimensional particle-in-cell simulations to explore this process in conventional flux bundle-type DFs, which are formed by single X line reconnection and connected to the Earth, and in newly proposed flux rope-type DFs, which are formed and bracketed by two X lines. In flux bundle-type DFs, electrons are betatron accelerated near the B_z peak, and ions are energized through reflection at the front. In flux rope-type DFs, most suprathermal electrons and ions are confined to the flux rope's magnetic structure and are accelerated through repeated reflections at the structure's two ends.