Research on the life-limiting sputtering mechanism of 30 cm ion thruster

Abstract

“Pits-and-grooves” patterns on the downstream accelerator grid surface had a severe effect on the thruster life; however, the sputtering patterns on the decelerator grid upstream surface were also observed after the thruster worked for over 3000 h. Reduction of the thruster diameter was adapted to prevent the erosion rate at the decelerator grid, but it decreased the thruster performance. Therefore, balancing the lifetime and performance was so critical for the optimization design of ion thruster. A three-dimension numerical model was established, and a Particle-In Cell-Monte-Carlo-Collision method was applied to investigating the hitting process and sputtering mechanism of a 30 cm ion thruster. Based on the experimental beam ion density profile in the plume, ion optics was divided into three regions, where the center region accounted for 73.3% of the effective extraction diameter of 30 cm. Beam ions in the center and the center-edge region were focused very well, and no ions striked directly on any grid surface, whereas ions at the edge were under-focused and had a cross-over interception. Decreasing the screen grid diameter from 13 to 12 could reduce the maximum erosion depth of the decelerator grid from 1.0 × 10−3 to 9.0 × 10−4, which only resulted in a 0.03% decrease of thruster performance. The maximum erosion depth of the accelerator grid caused by charge exchange xenon ion bombardment was 1.0 × 10−3 locating in the center region, which was twice that of 9.0 × 10−4. Improving the flatness was the way to extend the thruster lifetime. The maximum error of simulation was about 4.38%. The simulation results can provide technical reference for the optimization design of the ion thruster.