Strong Field‐Aligned Current and Its Driven Energy Conversion at Anti‐Dipolarization Front

Abstract Anti‐dipolarization fronts (ADFs), characterized by the rapid increase of the negative magnetic field B z component, are typically formed at the leading edge of the tailward reconnection jets in the Earth's magnetotail. To date, the electron‐scale current structures, which govern the energy conversion at ADFs, are still barely understood due to the lack of high‐resolution measurements. Here, using Magnetospheric Multiscale mission, we for the first time report a tailward ADF associated with strong field‐aligned current (FAC). The FAC appears at the leading part of the ADF and its densities can reach about 200 nA/m 2 , which is significantly larger than those reported before. Such current is primarily contributed by the electron flow, which also forms electron beam distribution in the anti‐parallel direction. Significant energy conversion ( E ⋅ J , E is electric field and J is current density) is also observed at the ADF, which is mainly contributed by the FAC and the fluctuating electric fields. This study makes essential steps toward understanding the current system and the energy conversion at the ADF in the Earth's magnetotail.