20A发射电流空心阴极小孔区等离子体特性研究

Plasma Characteristics in Orifice Region of 20A

关键词:  离子推力器  空心阴极  小孔区  等离子体特性

Key words:  Ion thruster  Hollow cathode  Orifice region  Plasma characteristics

摘要:

为了获得30cm口径离子推力器20A额定发射电流空心阴极工作时小孔区的等离子体特性参数，并验证现有阴极小孔结构设计下的阴极电流发射能力，采用数值模拟及有限元分析方法研究了空心阴极小孔区的等离子体特性参数。结果显示:空心阴极小孔区的中性原子密度基本在4×1021～6×1021/ m3，分布较为均匀且越靠近小孔出口区域的原子密度越低；当阴极发射体温度为1800K时，采用等离子体零维扩散模型得到阴极小孔区轴向平均电子温度约为2.66eV，且靠近阴极顶小孔出口方向电子温度相对较高，从小孔区入口至出口电子温度增幅在1～2eV；通过离子连续性方程得到阴极孔区内，等离子体密度约在1×1021～1.4×1021/m3，靠近出口处的等离子体密度降低较为明显；通过电子连续性方程，得到小孔区入口处的电子电流约为7.2A，而出口处的电子电流约为11.6A，与性能测试试验结果一致，电子电流增益系数约60%；离子电流密度峰值约为6.16×106 A/m2，出现在距离小孔入口约0.5mm处。通过理论分析认为，阴极孔区的腐蚀特点是靠近出口处的直径在离子腐蚀作用下不断地扩张，并在扩张到一定程度后，孔区出口处被腐蚀后的直径将不会再发生变化，理论分析腐蚀趋势与兰州空间技术物理研究所研制的LHC-5阴极小孔区寿命试验腐蚀情况基本一致。

Abstract:

In order to obtain 30cm diameter ion thruster's 20A emission current hollow cathode's plasma characteristics in orifice region and verify the current emission ability in existence structure design of orifice，numerical calculation method and finite element method were used to study plasma characteristics in orifice region of hollow cathode. The obtained results indicate that neutral density is in range of 4×1021/m3～6×1021/m3，which is well-distributed and neutral density is lower closed to the exit of orifice. When emitter temperature is 1800K and the average radial electron temperature is about 2.66eV by plasma diffusion 0-D model and which is higher closed to exit of orifice，and electron temperature is increasing about 1～2eV from orifice entrance to exit. Orifice region plasma density is in the range of 1×1021～1.4×1021/m3 by using ion continuity equations and plasma density decreasing obviously closed to exit of orifice. Electron current is about 7.2A closed to the entrance of orifice region and which is 11.6A closed to exit by using electron continuity equations，the calculation results are in well agreement with the experimental results，electron current gain coefficient is about 60% in orifice region. The highest ion current density is about 6.16×106 A/m2 which is about 0.5mm closed to the entrance. Through theory analysis，the exit of hollow cathode orifice is badly erosion meanwhile the diameter of orifice is increasing by erosion effect. The orifice diameter erosion rate is fall to negligible levels once orifice opened sufficiently，theory predict results of erosion tendency is in agreement with LHC-5 hollow cathode life test results.