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.

Electron extraction enhancement via the magnetic field in a miniature microwave discharge neutralizer

“…PLEASE CITE THIS ARTICLE AS DOI: 10.1063/1.5127805 .0, and 8.0 mm) and diameters (1.0-5.0 mm). 25 As boundary conditions, the potential on the metal and boron nitride (BN) was set to zero and the potential at z = 10 mm was set to 20 V for the electron extraction voltage, which is the same voltage as in our previous experiment. 18 In addition, all electrons and ions disappeared at the wall, the antenna, and other boundaries, where no reflection or charge accumulation was assumed.…”

“…In the previous experiment, the extracted current increased with r, reached the maximum at r = 5.0 mm, and then decreased with r again. 25 Therefore, in this study, we moved the center position of the orifices between 5.0 and 6.0 mm. Figure 4 shows the magnetic field lines together with the circular and arc orifices, where the magnetic field lines passing through the orifice are denoted by solid lines and the others by dotted lines.…”

Engineering Model of the Miniature Ion Propulsion System for the Nano-satellite: HODOYOSHI-4

“…Both plasmas need the same amount of microwave power, typically 1.0 W each other. The detail of the discharge chamber was described in the reference [3][4][5][6][7][8] . Downstream end of the discharge chamber differentiates the ion beam source and the neutralizer.…”

“…This has been mainly impeded by two reasons: limitation of electrical power available on small spacecraft and difficulty to develop a miniature neutralizer suitable for a miniature ion thruster. A miniature and low-power ion thruster was developed using an ECR (electron cyclotron resonance) plasma by 4.2-GHz microwave to overcome the problems [3][4][5][6][7][8] . Utilizing the ECR plasma for ion thrusters gives advantages of longer life time and simplified structure 9,10) .…”

Development of the Miniature Ion Propulsion System for 50 kg Small Spacecraft

“…A miniature ion was thruster developed in Institute of Space and Astronautical Science in Japan Aerospace Exploration Agency (ISAS/JAXA) to overcome the above-mentioned problems [3][4][5][6][7][8]. Development of a new low power plasma source enabled to develop a miniature ion source and neutralizer driven by 1.0 W microwave power respectively.…”