氙气离子推力器束流等离子体特征参数的Langmuir单探针诊断

Single Langmuir Probe Dignostics for Characteristic Parameters of the Beam Plasma in Xe Ion Thruster

离子推力器和航天器的成功整合,需要对羽流-航天器之间可能的相互作用进行全面的评估。为了给二者的整合提供实验依据,设计使用了Langmuir单探针测试系统,对氙气离子推力器束流等离子体参数的空间分布进行了诊断研究。实验中使用栅极表面向外凸出的双栅极Kaufman型离子推力器,真空舱的背景压强为3mPa。与传统静态等离子体不同的是:离子推力器束流等离子体具有很大的定向速度,致使探针电流大幅增加,所以传统静态等离子体条件下的I-V(电流-电位)曲线的解释需要重新考虑并进行适当修正。为了尽量减少定向流对离子饱和电流的影响,实验中选择将Langmuir探针与推力器轴线平行放置。实验结果表明:离子推力器的束流等离子体的悬浮电位、空间电位、离子浓度的变化趋势相似,不同径向位置处的各参数都随着轴向距离的增加而减小。分布图中存在一些参数值较低的特殊点,是因为这些测点并没有位于等离子体束流区域内。通过这些特殊点的轴向和径向坐标,可估计出推力器的束流发散角(16.014°)、栅极半径(在71.3～111.3mm范围之内)、束流形状。

Successful integration of ion thrusters into spacecrafts requires comprehensive evaluation of the possible plume-spacecraft interactions between them.In order to provide experimental proofs for the integration,after designing and developing a single Langmuir probe system,we measured and analyzed the special distribution of beam plasma characteristics of a xenon ion thruster using the system.The Kaufman type ion thruster used in this experiment has twin grids that are convex outward.In the experiment,the background pressure was maintained at 3 mPa.Different from conventional quiescent plasmas,the ions in the beam had a very large directed velocity and would greatly increase the probe current.Hence,the standard interpretation of I-V curves should be reconsidered and revised.In order to minimize the directed current in the ion saturation current,the Langmuir probe used in the test was set parallel to the centerline of the ion thruster.Experimental results show that the trends of the floating potential,plasma potential,and ion density are similar： these values at different radial locations decrease with increasing axial distances.However,it is noticed that there are extremely low values in the profiles of floating potential,plasma potential,and ion density,because these points are not in the beam region.According to the axial and radial locations of these points,the beam divergence（16.014°）,grid radius（within 71.3~111.3 mm）,and beam configuration of the thruster can be estimated.