Improving the performance of a water ion thruster using biased electrodes. (October 2021)

• Record Type: Journal Article
• Authors: Ataka, Yasuho; Nakagawa, Yuichi; Koizumi, Hiroyuki; Komurasaki, Kimiya
• Is Part Of: Acta astronautica. Volume 187(2021)
• Page Start: 133
• Page End: 140
• Publication Date: 2021-10
• Subjects: 0000 -- 1111; Electric propulsion -- Ion thruster -- Water propellant -- Microwave discharge -- CubeSat; Astronautics -- Periodicals; Outer space -- Exploration -- Periodicals; Astronautics; Periodicals; 629.405
• DOI: 10.1016/j.actaastro.2021.06.020
• Languages: English
• ISSNs: 0094-5765

Abstract

Abstract: This paper investigates whether biased electrodes can improve the performance of a microwave-discharge water ion thruster, which has been proposed as a propulsion system for CubeSats. Previously, for several microwave ion sources, the beam currents have been increased by mounting a biased electrode in the discharge chamber. The effect of a biased electrode on a water ion thruster was unclear because its magnetic field profile and characteristic length compared with the microwave wavelength are different from those used in previous studies. To investigate the effect, a thruster was divided into three parts: magnets, a microwave antenna, and a discharge chamber, which is comprised of an electrically conductive sidewall and a screen grid. The parts were isolated electrically. Bias voltages from − 44 to ＋ 44 V were applied to the microwave antenna or magnets by an additional power supply. These bias voltages were applied with respect to the screen grid and sidewall voltage. A maximum screen current of 12.7 mA was obtained for an antenna bias voltage of 38.2 V. This is 2.3 times larger than the current without a bias voltage. This increase could be caused by a combination of an increase of plasma density and ion extraction efficiency. The plasma density could increase with the gain of the total absorbed power. The ion extraction efficiency could increase due to the change in the plasma potential distribution. Overall, the mass utilization efficiency of the water ion thruster increased from 3.3% to 7.9% and the discharge loss decreased from 280 to 150 W/A at the antenna bias of 38 V. The performance with water electron source was evaluated. The thrust force, specific impulse, thrust-to-power ratio, thrust efficiency were 190 μ N, 350 s, 5.9 μ N/W, and 1.0%, respectively at the antenna bias of 25 V. Highlights: The performance of the water ion thruster with biased electrodes was evaluated. The electric potential of magnets or an antenna inside the thruster was changed actively. The screen current increased from 5.4 to 12.7 mA with positive potential on the antenna. An increase of the plasma density and the ion extraction efficiency caused the performance improvement. With antenna bias, the specific impulse was 350 s, and thrust efficiency was 1%.