A study of the influence of different grid structures on plasma characteristics in the discharge chamber of an ion thruster

Abstract

The grid structure has significant effects on the discharge characteristics of ion thruster. The discharge performances of 30 cm diameter ion thruster with flat, convex and concave grids are studied. The analysis results show that the discharge chamber with a convex grid has a larger “magnetic field free area” than others, and the parallelism of magnetic field isopotential lines and anode is basically same in the three models. Plasma densities of the three structures at the grid outlet are in the range of 3.1×1016‒6.9×1017 m−3. Along the thruster axis direction, the electron temperature in the chamber with convex and concave grid is in the range of 3.3‒3.5 eV, while that with a flat grid is lower, in the range of 3.1‒3.5 eV. In addition, the convex grid and the concave grid have better uniform distribution of electron temperature. Moreover, the collision frequency ratios show that axial ionization degree of the three models is the highest, and the flat grid has the highest discharge efficiency, then the convex grid, and the concave grid is the worst. The test and simulation results of 30 cm diameter ion thruster with convex grid show that the measurement and calculation results are 3.67 A and 3.44 A respectively, and the error above mainly comes from the ignorance of the double charged ions and parameter setting in the model. The comparison error between simulation and measurement of beam current density is mainly caused by the actual thermal deformation of the grids during the discharge process, which leads to the change of electric potential distribution and the variation of focusing characteristics of the grids. With the consideration of discharge performance and the thermal grid gap variation, it can be concluded that the flat and concave grids are more suitable for small diameter ion thrusters, while convex grid is a more reasonable choice for the higher power and larger diameter thrusters.

A study of grid failure mode drivers and methods for accelerated life testing of a 30 cm diameter ion thruster

“…T ed is electron temperature downstream of the grids, and the electrons in this region are mainly from ionization in the plume region and emission of the neutralizer. V p is the plasma potential, which is set according to the calculation result of the plasma sheath potential [19].…”

“…At present, the special lifetime acceleration verification of adjusting the background pressure in the vacuum chamber has not been carried out, but the simulation results can be verified through the performance test and life test of a 30 cm diameter ion thruster in different vacuum facilities. From 2017 to 2021, two 30 cm diameter ion thrusters (number M04 and M06, with newly installed grids) were, respectively, subjected to 1500 h and 6500 h verification tests in the vacuum facility numbered TS-7 and TS-7A (as shown in figure 12) of LIP [13,19]. The TS-7 vacuum facility is 3.8 m in diameter and 8 m in length, which can provide a vacuum level of 5 × 10 −3 Pa when the thruster is under 5 kW rated condition.…”

Ion Electric Propulsion System Electric Breakdown Problems: Causes, Impacts and Protection Strategies

“…In the three stages, the surfaces of ion thruster grids could absorb gases and particles, resulting in micro-protrusion on the surfaces and frequent breakdown in the early stage of the thruster on orbit. However, due to the limited amount of gases and particles adsorbed on the surfaces of grids, the gases and particles on the surfaces of ion thruster grids would gradually desorb with a high temperature [42]. Thus, the frequency of breakdown caused by the absorbed gases and particles will decrease with the increasing working time of the ion thruster.…”