A novel method to increase the self-bias voltage in RF-biased ion thrusters

The RF-biased ion thruster is a promising method for achieving self-neutralization. However, the thruster performance is constrained by the limited self-bias voltage, which tends to degrade due to capacitive coupling between the screen grid and the discharge chamber wall. This paper proposes a novel method to enhance the self-bias voltage by adding a screen grid extension ring between the screen grid and the discharge chamber. Experimental results demonstrate that this method significantly improves the self-bias voltage, with maximum value increased from approximately 100 V to 250 V. Crucially, the enhancement mechanism is evaluated under different thruster operational stages: initially via geometric expansion, and subsequently in the steady-state via a circuit topology transformation induced by the synergistic interaction between the extension ring and the deposited film on the discharge chamber wall. Steady-state stability test confirms that this synergy ensures the self-bias voltage remains maximized and stable, independent of continuous film accumulation. Measurements of the plasma parameters and estimated thrust demonstrate that this method significantly improves the thruster performance at higher grid power levels, yielding an estimated thrust approximately twice that of the configuration without the extension ring, without compromising plume neutralization, offering a practical solution for improving the performance of RF-biased ion thrusters.