Neutral Plume Simulation of Ion Thruster in Vacuum Facility With Cooled Target

Abstract

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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> 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.