The background pressure of vacuum chamber determines operation and performance of ion thrusters. In order to present the neutral plume and temperature distribution of a 30-cm-diameter ion thruster working under rated condition and in a large vacuum facility, theoretical calculation and numerical simulation are used to investigate the characteristics of thruster neutral plume. The results show that the neutral plume can be treated as an oriented molecular flow. Both theoretical calculation and numerical simulation results show that axial temperature profiles of neutral plume on the center line of facility decreases very slowly; however, in the area near the ion cooled target, temperature rapidly decreases from 500 to 100 K. In terms of pressure, it is found in both results that when the thruster is working, the vacuum degree of the chamber is in the order of 10−3 Pa. The simulation result, however, obviously shows the vacuum degree in the area near the thruster outlet and cooled target is higher than that in the middle area. The velocity of the neutral flow appears directional and decreases almost exclusively along the center line of the facility. The simulation results present a similar trend and agree well with the experimental results, and the comparison error is less than 10%. However, the calculations have some errors with the experimental results due to neglecting the absorption effect and energy deposition of the ion cooled target to neutral atoms. The study shows that numerical simulation can better describe the neutral plume expansion map of the facility, and the theoretical calculation can be used to roughly estimate neutral plume characteristics.

中文翻译：

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带冷却靶的真空设施中离子推进器的中性羽流模拟

真空室的背景压力决定了离子推进器的运行和性能。为了呈现30cm直径离子推进器在额定条件下和大型真空设施中的中性羽流和温度分布，通过理论计算和数值模拟研究了推进器中性羽流的特性。结果表明，中性羽流可被视为定向分子流。理论计算和数值模拟结果均表明，设施中心线上中性羽流轴向温度分布下降非常缓慢；然而，在靠近离子冷却目标的区域，温度从 500 K 迅速下降到 100 K。 在压力方面，两个结果都发现，当推进器工作时，腔室的真空度在 10-3 Pa 左右，但仿真结果明显表明，推进器出口和冷却靶附近区域的真空度高于中间区域。中性流的速度看起来是有方向的，并且几乎完全沿着设施的中心线降低。仿真结果呈现出相似的趋势，与实验结果吻合较好，比较误差小于10%。然而，由于忽略了离子冷却靶对中性原子的吸收效应和能量沉积，计算与实验结果存在一定误差。研究表明，数值模拟可以更好地描述该设施的中性羽流扩展图，