Three-dimensional particle in cell simulation of multi-mode ion thruster optics system

The optics is one of the main components of an ion thrust, which influences the performance and thruster lifetime. The operation of ion thruster can be evaluated by numerical simulation based on the current-voltage entrance condition, especially for thruster with a variety of operating modes. The plasma transport process is simulated with 3D-PIC (particle in cell) method for a two-grids optic. The performances of the NSTAR thruster under different operating modes are calculated and compared with the results of in-orbit test, verifying the correctness of the simulation mode. The influences of operation modes on the electric field distribution and the beam state are analyzed, and the requirements of multi-mode design for ion thruster are discussed. The results show that a convex sheath and concave zero equipotential surface away from the optic, low value of "saddle point", and gentle downstream potential distribution, which help to improve ion pass rate, suppress electronic reflux and reduce Pits-and-Grooves corrosion, are the target of ion thruster mode design. Increasing beam voltage will result in a high loss caused by the divergence angle, and extend the beam current range for a good operation condition. For a large beam current mode, high beam voltage will make the beam have a better "focus" state, and reduce the Barrel corrosion. The results will provide a reference for the operation mode design for the multi-mode ion thruster.