Investigation of ion back flow by Hybrid-PIC simulation considering experimental current density distribution at the conductive surface for microwave discharge ion thruster

10 cm class microwave discharge ion thruster has been installed in the asteroid probe Hayabusa2. From the operational history, it was found that the conductive surfaces were sputtered. It is expected that the main cause of sputtering is the ion backflow. As ground-experiment have shown that the ion sputtering is detrimental to cathode, it is crucial to investigate the physical process of the ion back flow. In this work, both experimental and numerical approaches are performed. In numerical simulation, electron is treated as fluid model with quasi-neutral approximated drift-diffusion, and ion is treated as particles, i.e., Hybrid-PIC. To consider the boundary condition with finite current density at the conductive surface, the distribution of current density at the conductive surface is experimentally measured. The combination of experimental and numerical simulation can reproduce the potential profile, and capture kinetic ion dynamics with low computational cost.