7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Operating a magnetron sputtering electric propulsion device with a pulsed
gaseous water propellant
Sota Shimizu1 and Kazunori Takahashi1,21Department of Electrical Engineering, Tohoku University
2
National Institute for Fusion Sciencee-mail (speaker): sota.shimizu.t6@dc.tohoku.ac.jp

The number of small satellites represented by CubeSats
has significantly increased in the last few decades. The
key technology to success missions using small satellites
is realization of a small electric propulsion system (EP)for their attitude and orbit control, de-orbit, and so on [1].
Many types of small EP devices have been investigated inindustrial and scientific fields, being represented bypulsed plasma thrusters, gridded ion thrusters, vacuum arc
thrusters, and so on [2-4]. They have a common technicalchallenge for their size and power limitation (~ a few tensof watts).
Magnetron sputtering has been widely used insemiconductor manufacturing. Applications of gasless orbipolar-voltage-applied magnetron sources to EP havebeen proposed [5]. A recent study with a dc magnetron
sputtering (DCMS) has demonstrated the thrustgeneration by exhausting the metallic target material,
where the argon gas is fueled to sustain the discharge. As
the sputtered and exhausted particles are electricallyneutral, a neutralizer-free EP system can be achieved [6].
When operating with high power impulse magnetron
sputtering (HiPIMS), the thrust decreases because ionized
sputtered atoms go back to the cathode and are not ejectedfrom the system, which is a phenomenon called selfsputtering [7]. Furthermore, a water-fueled magnetron
sputtering source has also demonstrated the thrustgeneration [8]. While the thrust in the water-fueled
operation is lower than that for an argon-fueled source dueto the power consumption for dissociation of watermolecules, it does not require a high-pressure gas tank forpropellant storage and would meet the criterion forcompact EP. Various kinds of liquid and solid propellants
have been investigated owing to their advantages indeveloping a compact thrust system. In addition, water is
one of the most suitable propellants in terms of its safety,
abundance, and the ease of use [9].
A propellant gas feeding system, which requires smaller
size besides accurate control of mass flow rate, also plays
an important role in a small EP device. In the authors’previous study, water-propellant is introduced by a mass
flow controller constantly [8]. In the present study, tominimize the size of the gas feeding system, a mass flow
controller is substituted by a pulsed valve, and the quantityof the introduced propellant gas is controlled by a pulse
width of the gas valve as shown in Fig.1. A previously
reported target technique is used to assess the impulse bit[10].
A constant dc voltage (500-1000 V) is supplied between
the anode and cathode through a resistor of 1 k. When
the water vapor is introduced to the plasma source, a ringshaped plasma is produced. The pulsed valve is opened

Fig.1 Schematic diagram of experimental setup.
for 5-15 msec and the discharge is sustained for 100-500
msec, which depends on the supply voltage at 500-1000 V.
The target measurement shows the maximum impulse bitof 0.1 mN∙s, where the impulse bit due to the rare water
propellant is eliminated. The thrust-to-power ratio isroughly corresponded to that for mass flow controller
operation.
A change in the discharge impedance, i.e., the discharge
mode, is observed during the discharge pulse. To
investigate the effect of the mode change on the thrustgeneration, a temporally resolved measurement of theimpulse bit is performed. The result shows that the linear
correlation between the impulse bit and the discharge
power is confirmed. The detailed discharge characteristics,
the measurement technique, and the assessed impulse bit
will be presented.
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