Three-dimensional IFE-PIC numerical simulation of background pressure's effect on accelerator grid impingement current for ion optics

A three-dimensional numerical simulation modeling is developed to investigate the background pressure's effect on the characteristics of ion impingement on the accelerator grid for the ion optical system. The immersed-finite-element particle-in-cell (IFE-PIC) method is combined with Monte Carlo method to compute the electric field, track the ions, and describe the charge-exchange collision process while direct simulation Monte Carlo (DSMC) method is adopted to simulate the motion of neutral atoms. Results show that the residual neutral atoms in the vacuum chamber play an important role in the neutral atoms distribution when the background pressure is higher than a specific magnitude, and the accelerator grid impingement current increases with the increase of the background pressure. To improve the reliability of ion thruster service lifetime prediction in the ground life tests, the background pressure in the vacuum chamber should be below 10^-3 Pa.