Voltage waveform dependences on thrust performances in a Hall thruster
Tomohiro Ichimaru
Advanced Space Propulsion Lab.
1.

Introduction

Space applications such as weather observation
systems, telecommunication systems, GPS, areessential for our lives nowadays.1) Satellites need
propulsion devices to control its attitude and orbit.
There are candidates of propulsion system, and theHall thruster is the most expected electric
propulsion.2) The Hall thruster has both high thrust
efficiency (more than 50 %) with high specificimpulse (1000 - 3000 s), and higher thrust density
than ion thrusters because of the existence ofelectrons in the ion acceleration zone.
In the previous study, the new PPU (PowerProcessing Unit) concept for Hall thruster
operations has been proposed. Generally, a constantvoltage is used for the power source of Hallthrusters. While, the proposed PPU, we called
harmonized PPU, provides fluctuating voltages inaccordance with discharge current oscillation inHall thrusters. When the harmonized PPU is used,better thrust efficiency and thrust to power ratio areachieved compared to the case of DC power source.
This trend results from the considerable reductionof the power consumption.3)
The reason why the performances are improved
using the harmonized PPU has not been clarified.
In addition to that, the voltage waveform has notbeen optimized yet. Therefore, the purpose of thisstudy is to investigate above two subjects.
2.

are fixed at 10.4 sccm and 2.8 sccm, respectively.
Fig. 3 shows the applied voltage waveform. The
rectangular wave is generated by a function
generator, and it is added to the base voltage which
is made by a DC power supply through a power
amplifier. Base voltage and amplitude are set to 150
V and 25 V, respectively. In the frequency response
analysis, sin wave is applied. Also, base voltage,amplitude, inner coil current, and outer coil current
are set to 200 V, 5 V, 0.4 A, and 1.6 A, respectively.

Fig. 1 Experimental system

Experimental Setup

The whole experiment system is shown in Fig.1.
A 1 kW magnetic layer type Hall thruster
developed at Kyushu University (Fig. 2) is used inthis experiment. The inner diameter and the outer
diameter of the acceleration channel are 48 mm and72 mm, respectively. Four solenoidal coils set
outside, a solenoidal coil set inside, and a magnetic
pole made of soft iron make a radial magnetic field.
The Hall thruster and the hollow cathode on thethrust stand are in the vacuum chamber whosepressure is about 2.29×10-2 Pa when Xe inflow.
Inner and outer coil currents are set as 0.6 A and 2.4
A, and mass flow rate to the thruster and cathodeFig.2 Hall thruster

Fig. 3 Applied voltage waveformResults and Discussion

Because voltage waveforms vary with frequency
in the previous study, the performance
improvement factor is not clear. While, it issuggested in this study that current phase lags
improves efficiency.
The results contribute to optimizing parametersof the PPU developed in the previous study.

Efficiency

0.20

0.15
891011121314Frequency (kHz)Fig.5 Effect of frequency (Duty ratio: 0.8)200

Impedance
Phase

100

Phase (deg.)

150
50
100
050-5004

68-10010 12 14 16 18 20 22Frequency (kHz)Fig. 6 Frequency response analysis
250Voltage
Current

10200
5150

100
050-0.3

0.00.3Time (ms)Fig. 7 Voltage and current trace (0.8, 12 kHz)

0.30

References

0.25

Efficiency

0.25

Current (A)Conclusion

4.

0.30

Impedance (ohm)Fig. 4 shows the duty ratio dependence on
efficiency in the frequency of 12 kHz. When theduty ratio is less than 0.3, the Hall thruster cannot
maintain discharge in this experimental condition.
The average voltage becomes high as the duty ratio
increases. Then, ions are accelerated efficiently andare generated a lot. As a result, efficiency increases
with the increase of duty ratio. At duty ratio of 0.8,efficiency is improved around 35 % in comparison
with DC.
Fig. 5 shows the frequency dependence on
efficiency in the duty ratio of 0.8. Current phasevaries with frequency because Hall thrusters havethe characteristic such as a serial resonance circuit.
That is clarified by the frequency response analysis
shown in Fig. 6. When the current phase lags in anadequate range such as Fig. 7, efficiency become
high. The frequency of 12 kHz offers the best
efficiency in this experimental condition. It is alittle higher than the original frequency ofdischarge current oscillation, 8.7 kHz. If the current
phase is almost same to voltage phase, the power
consumption is large, and if the current phase lags
too much, the thrust decreases. Owing to the tradeoff between two, there is an optimum frequency.

Voltage (V)

3.

0.20

0.15

0.10
0.4

0.5

0.6

0.7

0.8

0.9

1.0

Duty ratio

Fig. 4 Effect of duty ratio (Frequency: 12 kHz)

[1] T. Maeda, et al.: Launch Result and Current
Status of "KIZUNA, IEIICE Technical Report
SANE 2008-19, 2008. (in Japanese)[2] V. V. Zhurin, et al.: Physics of Closed DriftThrusters, Plasma Sources Sci. Rechnol. 8,
R1-R20, 1999.
[3] N. Yamamoto, et al.: Development of a Novel
Power Processing Unit for Hall Thrusters,IEEE Transactions on Plasma Science, Vol.43,
No.1, 2015.