Abstract: In order to obtain the effects of a three-grid assembly design parameters on expected lifetime for 30cm diameter ion thruster，Particle-In-Cell-Monte Carlo Collision (PIC-MCC) method is used to calculate the ion mass sputtering velocity，which is also used to build the 2-D lifetime estimation model and lifetime influence estimation on the basis of failure mode analysis results. The results show that the main failure mode of the three-grids is early structure failure by direct ion bombardment under 5kW work mode，and the rapid ion erosion of the decelerator grid becomes the key factor to influence the lifetime of 30cm diameter ion thruster. Furthermore，different work modes will not bring new failure modes，which only affect the sputtering velocity and lifetime of the grids. The ion beam is in an obvious over perveance condition when the thruster is in working state under the existing design parameters，and the estimated lifetime of the accelerator grid and the decelerator grid are 9062h and 2642h，respectively. The PIC-MCC simulation results of the influence of three key design parameters on the grids expected lifetime show that voltage reduction of the accelerator grid has minor effect to improve the lifetime of decelerator grid. The ion sputtering velocity decreases with the reduction of the cold gap between the accelerator grid and the decelerator grid，and the lifetime increased to 10726h by decreasing the cold gap from 1mm to 0.6mm in 5kW work mode. Meanwhile，the thruster can endure the mechanical environment test under this gap. Decreasing the diameter of the screen grid hole has a significant effect on ion beam shape by PIC-MCC calculation results，and the ion beam divergence angle of a single hole is effectively suppressed by decreasing the diameter of the screen grid hole，then the ion beam almost never bombard upstream of the decelerator grid again. The estimated lifetime of the decelerator grid can be improved to 9259h by decreasing the diameter of the screen grid hole from 1.9 mm to 1.6 mm. The analysis results provide reference for life optimization design of the three-grids assembly for 30cm diameter ion thruster.

Key words: Ion thruster；Three-grids assembly；Design parameters；Lifetime estimation

摘要： 为了研究30cm离子推力器三栅极组件设计参数对预估寿命的影响，在完成失效模式分析的基础上，通过PIC-MCC方法对离子推力器三栅极组件的离子溅射速率进行了计算，建立起栅孔二维寿命预估模型，并针对栅极设计参数对预估寿命的影响进行研究。结果显示:导致三栅极组件的主要失效模式为5kW高功率模式下的离子直接轰击所造成的栅极早期结构失效，且减速栅的过快离子溅射腐蚀成为影响三栅极组件寿命的关键，而不同工作模式不会产生新的失效方式，仅影响栅极的离子溅射速率以及寿命；在现有三栅极设计参数条件下，当推力器工作时，栅极引出的离子束流处于明显欠聚焦状态，且加速栅寿命预估值约为9062h，而减速栅约为2642h；通过PIC-MCC方法得到的栅极三个关键设计参数对寿命的影响模拟结果显示，降低加速栅电压对提升减速栅寿命的作用较小；缩小加速栅与减速栅冷态间距后，离子溅射速率会随着冷态间距的缩小逐渐降低，冷态间距由1mm缩小至0.6mm后，减速栅在5kW工况下的工作寿命可提升至10726h，且经试验验证该间距可满足推力器力学环境试验要求；缩小屏栅孔径对改变离子束流引出形状具有显著作用，单孔束流发散角度随着屏栅孔径的缩小出现了明显降低，且束流离子几乎不会再直接轰击至减速栅上游区域，当屏栅孔径由1.9mm缩小至1.6mm后，减速栅工作寿命可提升至9259h；分析结果对后续开展栅极组件的寿命优化设计提供了参考。

关键词: 离子推力器；三栅极组件； 设计参数； 寿命预估