The lunar polar region has become the focus of future explorations due to the possible ice reservoir in the permanently shadowed craters. However, the space environment near the polar region is quite complicated due to the topographic shielding, and a plasma mini-wake can be caused by a polar crater. So far, three-dimensional (3D) simulation of the mini-wake around a crater far larger than the Debye length is still absent. Here we present a 3D electrostatic hybrid particle-in-cell model to study the plasma mini-wake of a polar crater on scale of about 1 km. It is found that the mini-wake can begin upstream from the crater with a cone angle of about 8.8º. There is a plasma void with extra electrons near the leeward crater wall, where the electric potential can be as low as -60 V. About 4% of solar wind flux can be diverted onto the crater bottom and about 18% of solar wind flux can be diverted onto the windward crater wall, which provide an important source for the surface sputtering. Further studies show that the mini-wake can change with the solar wind parameters and the crater shapes. Our results are helpful to evaluate the space environment and the water loss rate of a polar crater, and have general implications in studying the plasma mini-wake caused by a crater on the other airless bodies.
 

太阳风；月球极区；迷你尾迹