Development of low power capacitively coupled radio frequency thruster

Abstract

A low power capacitively coupled radio-frequency thruster (CCRFT) with a dielectric capillary is being developed and investigated at the University of Southampton (UoS). The thruster utilizes a non-symmetric electrode arrangement and a radio-frequency generator with an automatic matching network. The small diameter of the dielectric capillary allows operation of the device in very low flow rates. When the thruster was operated in front driven electrode configuration at 13.56 MHz, the DC bias was found to develop in accordance with classical theory of asymmetric capacitive discharge. The effect of argon flow rate on ion energy distribution function (IEDF) is also analysed using retarding potential analysis. The IEDFs depict double peak structure for low flow rate, and at < 10 SCCM showed the dominating effect of charge exchange collision and radio frequency modulation. At constant rf output power of 10 W, the ion content in the plume of the CCRFT is measured to have negligible contribution towards thrust generation. The estimated electron temperature in plasma bulk is ~3.2 eV which increases near the driven electrode to ~8.4 eV, with plasma density of the order ~10¹⁹ m^-3.
It is planned to continue experimental campaign and characterize the overall performance of the thruster using thermal measurements, direct thrust measurements and optical emission spectroscopy. The thruster’s operation in reverse polarity with varying inter-electrode will also be carried out and its effect on propulsive performance analysed. Fluid plasma simulations are also being developed for comparison with experimental results.

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