Research On The Erosion Of Ion Thruster Accelerator Grid Based On The Seven Aperture Model

Since21st century, ion thruster has been widely used for propulsion systemin various space missions. Contrast to the traditional chemical thruster, longlifetime is the most notable feature of the ion thruster. Hence, a key issue in theion thruster performance evaluation is the service lifetime of the thruster. As animportant component of the ion engine, the grid system failure is the main reasonto limit the lifetime of the ion thruster, it is caused by the sputter erosion whichis produced by the CEX ions impingement on the accelerator grid. In the groundlife tests, the background pressure in the vacuum chamber will affect theoperation process of the ion thruster in the simulation space environment. Onlyfully explore the physical mechanism of the background pressure's effect on theground life tests, can we make an accurate prediction and evaluation of the ionthruster lifetime in the outer space.In this paper, a three dimensional simulation code based on the seven-holeaperture model is developed to investigate the ion thruster operation process. TheIFE-PIC method was used to track the ions motion in the grid system, the DSMCmethod was adopted to simulate the distribution of the neutral atoms, and theMCC method was adopted to simulate the charge-exchange collision process.The simulation results of the accelerator grid impingement current underdifferent background pressures show that, in the ground life tests, the residualneutral atoms due to the background pressure in the vacuum chamber affects thegeneration process of the CEX ions, which will contribute to the change of theaccelerator grid impingement current. When the background pressure in thevacuum chamber reaches a specific magnitude, the accelerator grid impingementcurrent increases dramatically. At last, the accelerator grid erosion depth iscalculated according to the erosion simulation model. The erosion simulationresults show that the erosion depth rise with the increase of the backgroundpressure, the distribution of the accelerator grid center-hole surface erosion depthwhich along the circumferential direction is relatively uniform, while greateredge-hole surface erosion depth are shown in the region more toward the opticscenter.According to the numerical simulation results, in the ground life tests, thebackground pressure in the vacuum chamber has a significant influence on boththe accelerator grid impingement current and the accelerator grid erosion, toeliminate errors caused by the background pressure and accurately predict the ion thruster service life in the outer space, the background pressure in the vacuumchamber should properly be controlled within a certain range.