Abstract: The divergent magnetic field ion thruster typically leads to non-uniform beam profile observed in experimental measurements. In this study， an optimization scheme of the screen grid by varying the aperture diameters， matching the distribution of plasma density and electron temperature in discharge chamber， was proposed in order to improve plasma uniformity. Based on the PIC/MCC method， beam characteristics of the optimization design， including potential， ion density and beam flatness， were simulated comparing with current design. Comparisons illustrate that axial electric field intensity， beam diameter and ion density decrease， and absolute value of saddle-point potential decreases for 1.8V， beam focus shifts inward at central region of optimization optics system. Contrarily， axial electric field intensity， beam diameter and ion density increase， beam focus shifts outward at outer region. Beam flatness has risen to 0.57 from 0.41， and divergence angle has dropped. It is concluded that the reliability of ion thruster has improved.

Key words: Ion thruster；Divergent magnetic field；Optics system；Variable aperture diameters；PIC/MCC

摘要： 为了改善发散场离子推力器束流均匀性，提出与放电室等离子体密度和电子温度分布相匹配的变孔径栅极设计方案。采用粒子云网格法(PIC)和蒙特卡洛碰撞(MCC)结合的数值计算方法(PIC/MCC)对变孔径设计方案进行仿真，并与现有设计仿真结果进行对比，分析两种设计不同分区电势、离子密度和束流平直度等参数特性。计算结果表明，相对于现有设计，变孔径设计栅极中心区域轴向电场强度变小，鞍点电势绝对值降低1.8V，离子聚焦点内移，离子密度降低，束径变小；边缘区域电场强度增大，聚焦点外移，离子密度提高，束径增大。引出束流发散角变小，平直度由原来的0.41提升至0.57，离子推力器可靠性得到有效提高。

关键词: 离子推力器；发散场；栅极系统；变孔径；PIC/MCC