Radio-Frequency Ion Thrusters-Power Measurement and Power Distribution Modeling

We present a methodology to measure the power delivered to sustain an inductive plasma discharge inside radio-frequency ion thrusters. This measurement is performed in real time near the coil within the resonant circuit using a patented low-noise radio-frequency voltage and current sensor system. With knowledge of the actual forwarded power, the efficiency of the generator under consideration, including the power feed cable, is assessed in real time. The variation of the power-to-thrust ratio can thus be understood more clearly since its value is given by physical changes of the plasma properties as well as the quality of the impedance bridge between the generator and plasma load. The latter can directly be determined by the proposed methodology, while the influence of the plasma parameters on the power-to-thrust ratio is obtained by means of a numerical model that is used in postprocessing to assess the power distribution within the thruster.