等离子体密度对栅极系统束流影响分析

针对现有离子推力器栅极系统束流引出分析中未考虑放电室等离子体密度均匀性影响的不足,基于数值方法对该问题进行了研究。采用单元内粒子(Particle In Cell,PIC)方法对栅极系统束流引出进行了数值模拟。PIC方法中电场求解采用有限差分方法,离子加速方法采用跳蛙格式。以国产20cm Xe离子推力器作为算例,计算得到了栅极中心和边缘孔引出束流离子和电场的分布。结果显示栅极中心孔相对边缘孔束流聚焦性好,束流发散角小,但中心孔轴线的鞍点电势较边缘孔高24.8V。因此,放电室等离子体密度分布对束流引出具有重要影响,电子返流现象最先出现在栅极中心位置。

Effect Analysis of Plasma Density on Ion Beam Extracted by Grid System

Present analyses on the ion beam of the grid system do not take account the plasma density in discharger chamber.Ion beam extraction was simulated by the particle in cell(PIC) method.The electric field was calculated by the finite differential method(FDM),and the ion particles were accelerated by the leap-frog method.With Chinese 20-centimeter Xe ion thruster,the electric potential and ion beam distributions in the center and brim aperture of grid system were obtained.The results show that the ion beam extracted by the center aperture has better focus property and smaller divergence angle than that of the brim ion beam.However,the saddle point potential of the center aperture is 24.8V,higher than that of the brim.Hence,the plasma density in discharger chamber has an important effect on the ion beam extraction,and electron back-streaming phenomena take place on the center position of grid system firstly.