离子发动机羽流空间电位诊断

Space potential diagnostic study of ion thruster's plume

离子发动机羽流空间电位分布不合理可能会造成一系列问题,以至于影响航天器的正常工作。试验使用发射探针对20 cm氙离子发动机束流区等离子体空间电位进行诊断,测点选取轴向距离发动机出口平面250~900mm,径向0~450mm,探针钨丝直径0.1 mm,加热电流1.5~2.5A。发射探针诊断建立在电子热发射基础上,因其I-V曲线拐点较朗缪尔探针更为明显,所以测量得到的空间电位分布更为准确。国外已经广泛使用发射探针测量等离子体空间电位,发射探针的试验数据处理方法仍存在较大分歧。从发射探针工作时的物理过程着手,分析热电子发射多少对空间电位诊断结果的影响,采用不同的探针I-V曲线处理方法并对各种方法利弊进行讨论,分析偏离真实空间电位的原因,比较得到较为合理的结果,对发射探针的结构改造和加热电流的选取提供依据,为发动机性能的改善和羽流仿真模型提供参考。

The plume plasma potential distribution of ion thruster could deeply affect the normal work of the whole spacecraft and cause some extremely serious problems.In our experiments an emissive probe was used to measure the beam plasma potential of a 20 cm-ion thruster using Xe as propellants.Experiments were performed at axial distances from 250 mm to900 mm downstream of the thruster＇s exit plane and radial locations ranging from 0 to 450 mm.The emissive probe based on thermionic electron emission was made of 0.1 mm-diameter tungsten filament with its heat current from 1.5 A to 2.5 A.The knee point of the emissive probe＇s l-V curve is clearer than that of the Langmuir probe,so the space potential distribution of our measurement results is more accurate.Emissive probe has been broadly used to diagnose plasma potential abroad,but lots of literatures indicate that there are still some divergences in the probe＇s data processing methods.The probe＇s working physical process of the probe was studied,and the effects of the emissive thermionic electron quantity on plasma potential diagnosis results were analyzed.Different processing methods of the probe＇s l-V curve were adopted and the advantages and disadvantages of each method were discussed.The reasons why measurement results deviate from the true plasma potential distribution were analyzed,which not only provide references for the structural reform of Emissive probe and the selection of heating current,but also give some suggestions for the plume simulation model and the improvement of thruster performance.