不同环境温度对30cm离子推力器三栅极组件的离子刻蚀速率影响分析

Effects of Different Ambient Temperature on Ion Erosion Rate for Triple Grid of 30cm Diameter Ion Thruster

为了对不同环境温度造成的30cm离子推力器三栅极组件离子刻蚀速率的影响进行分析,采用有限元仿真与试验验证相结合的方法,计算并试验验证了不同环境温度下的三栅极组件热平衡温度以及栅极间的相对位移变化,采用流体方法模拟了不同环境温度(20℃,-70℃,-120℃和-170℃)对三栅极组件的刻蚀影响,并结合短期寿命试验结果进行验证。结果显示:随着环境温度的降低,屏栅达到温度平衡的时间无变化,而加速栅温度平衡所需的时间则明显延长,20℃下的屏栅和加速栅热仿真结果与室温下推力器热平衡试验结果比对误差分别为7%和5%;其次环境温度的降低,会导致屏栅与加速栅的中心间距和边缘间距均缩小,而加速栅和减速栅的边缘间距却逐渐拉大,仿真结果与栅极热间距摄像测量结果符合性较好;根据三栅极组件的栅孔径扩大率随环境温度变化的计算结果来看,加速栅中心和减速栅边缘是离子刻蚀的主要位置,轰击至加速栅中心区域的离子数速率约是边缘的3倍,而轰击至减速栅边缘区域的离子数速率是中心的2.5倍,且环境温度的降低对加速栅中心区域离子刻蚀的影响更为强烈;经2100h的寿命试验验证,仿真结果与试验结果基本符合,误差经分析认为主要来自于流体方法的参数设置过程以及栅孔壁面均匀刻蚀的计算假设。

In order to obtain the effects of different ambient temperature on the ion erosion rate for the triple grid of a 30 cm diameter ion thruster,FEM(finite element method)simulation and test verification are used to obtain the temperature distribution and thermal deformation under thermal equilibrium.Meanwhile,fluid simulation method is used to simulate erosion of the triple grid in different ambient temperature(20℃,-70℃,-120℃,-170℃)and verified by short life time test.The results show that the time for the screen grid to reach temperature equilibrium is almost unchanged.However,it increases significantly for the accelerator grid as the ambient temperature decreases.The comparison error between the thermal simulation results of the screen grid and the accelerator grid with thermal equilibrium test at room temperature results of the thruster is 7%and 5%,respectively.The decrease in ambient temperature causes the hot gap constantly narrowing in the central area and the edge area between the screen grid and the accelerator grid.However,the hot gap in the edge area between the accelerator and the decelerator grid increases as the decreasing of ambient temperature,and the simulation results agree well with test results by video-metrics measurement method.According to the calculation results of aperture radius erosion rate in different ambient temperature,the central area of the accelerator grid and the edge area of the decelerator grid are the main ion bombardment locations.The velocity of the ions bombarding the central area of the accelerator grid is 3 times as that of the ions bombarding the edge,and the velocity of ions bombarding the edge area of the decelerator grid is about 2.5 times as that of the ions bombarding the central area.The impact of decreased ambient temperature on the ion erosion of the central region of the accelerator grid is more intense.According to verification of a 2100 h short time life test,the simulation results are coincident approximately,and the errors are mainly attributed to the parameters setting of fluid simulation method and the assumption of uniform ion sputtering on the wall of grid holes.