Switching Operation of Ion Beam Extraction and Electron Emission Using the Miniature Ion Thruster μ1

Abstract

Ion thrusters are promising propulsion devices not only for standard-sized spacecraft but also for small spacecraft. However, difficulty of the development of a miniature neutralizer has been a critical problem for miniature ion thrusters. We have proposed a novel ion thruster system to solve this problem. That is a switching operation, where a plasma source can select ion beam extraction or electron emission by electrical switching. The major challenge of this study is to find the method to effectively performs both functions from one plasma source. To match the system to small spacecraft, the both modes must be conducted using low microwave power and low mass flow as low as 1.0 W and 0.15 sccm. Firstly, fundamental characteristics of electron emission were investigated using an orifice plate. Based on this result, secondly, a special grid system for the switching operation was designed and examined. This grid system has two-different-size apertures for ions and electrons respectively. This grid showed high ion beam extraction performance, that is, 4.1 mA ion beam current at 1.0 W microwave power input. It also showed much higher electron current than the old grid system, although the electron current of 1.0 mA has not reached the targeted current yet. As a result, the experiment showed that the special grid system proposed here is an effective method to realize the switching operation.