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

Particle modelling of a miniature neutralizer-free radio-frequency ion thruster
for small satellite applications: revealing the mechanism of plasma generation,
ion acceleration and plume neutralization
Weizong Wang1,Yifei Li1,Chen Fu1
Advanced Space Propulsion and Energy Laboratory, School of Astronautics, Beihang University

Microsatellites have triggered a worldwide research
upsurge in recent years and due to its need for very smalland accurate thrust to achieve orbit control, the demand
for micro electric propulsion system is urgent. Radio
Frequency (RF) ion thrusters using a low pressure
inductively coupled plasma source have the advantages ofhigh specific impulse, easy to scale and long lifetime,
which are gradually applied to microsatellites as the lowpower electric propulsion system. Considering that thelifetime of neutralizer is a restriction for long time
operation of ion thrusters, a new technology forneutralizing the plume without external neutralizers has
been developed which simultaneously extracts positive
ions and electrons, using RF biasing instead of DC biasing
to the grid system of thruster. Regardless of widespreadattention to miniature neutralizer-free gridded ion thruster,little is known about its underlying operating mechanisms.
Therefore, we established particle-in-cell Monte Carlocollision (PIC/MCC) models to investigate the physics of
inductively coupled plasma generation, ion accelerationand plume neutralization respectively in a real-size
miniature neutralizer-free RF ion thruster which has been
benchmarked by comparing with the experiments. Theenergy relaxation characteristics of electrons in thedischarge chamber in response to the change of operating
parameters, i.e. RF coil current, gas pressure and appliedfrequency were widely investigated. The fundamental
physics of RF biasing including electron and ion spatial
and temporal dynamics during the ions acceleration andplume expansion were described and the influence of themisalignments of apertures on the grid system
performance was identified. This study lays a solid
foundation for further development of miniatureneutralizer-free RF ion thrusters for small satellite
applications. Figure 1 illustrates the distribution ofelectron and ion density in the real-size thruster (Icoil =14.55 A, f = 2.0 MHz, P = 1 mTorr) as well as the particle
number density in the DC and RF grid systems withmisalignments of apertures, respectively. This work is
supported by the National Natural Science Foundation ofChina (Grant Nos. 51977003 and 52277133).
References[1] Y.F. Li et al Plasma Sources Sci. Technol. 31 035009(2022).
[2] Y.F. Li et al Plasma Sources Sci. Technol. 32, 045014(2023).

Figure 1 Spatial distributions of low-pressure inductively coupled plasma properties (a) Electron density. (b) Ion density.
(c) Potential. (d) Absorbed power per cell in the discharge chamber (left figure) as well as the ion number density
distribution in the grid system (right figure) (a) Hole shift = 0 mm, DC, (b) Hole shift = 0.3 mm, DC, (c) Hole shift = 0mm, 13.56 MHz at ωt/2π = 0.75, (d) Hole shift = 0.3 mm, 13.56 MHz at ωt/2π = 0.75. The white dashed line in the rightfigure (a)–(d) represents the centerline of the ion beam. The black angle in the right figure (d) represents the deflection
angle of the beam centerline about the positive x direction. The red dashed lines in the right figure (d) represents the upperboundary and lower boundary of the ion beam, in which 95% of ions are contained. The rectangles appearing in thefigures show the position of grids.