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Radiofrequency excitation in single-stage Hall Effect Thrusters is proposed as a method to increase the performance of these devices. The topology of the magnetic and electric field within Hall Effect Thrusters makes it possible to excite quasistatic waves which travel longitudinally through the channel across a magnetostatic field, whose resonances are found at the electron cyclotron gyrofrequency and its upper harmonics. An in-house pseudo 2-dimensional axial–radial Particle-In-Cell software developed at the Imperial Plasma Propulsion Laboratory called PlasmaSim is verified and validated against the Russian thruster SPT-100 and adapted to be used as a computational tool to analyze plasma-wave interactions. A benchmark case study for 2-dimensional axial–radial plasma simulation codes is proposed, and PlasmaSim plasma in-channel properties are evaluated in this analysis. In terms of performance, comparison between simulated and experimental measurements shows average values in agreement with thrust, specific impulse and anode efficiency, over the full range of discharge power conditions of the SPT-100. The proposed method of radiofrequency excitation is to vary the ground reference potential of the neutralizing hollow cathode at high frequency. A range of potential excitation frequencies is established on the basis of hot plasmas’ theory, with candidate frequencies varying between 0.1 GHz to 2 GHz for the plasma conditions within a SPT-100 device. Simulation’s results give a deeper insight into the nature of these waves and their propagation in the plasma. Quantitative analyses as a function of power and excitation frequency are reported, showing the impact on thruster performance and in-channel plasma properties. The thruster’s total power is taken as the sum of the DC discharge power and AC radiofrequency power, which is calculated numerically from the simulation results based on the time varying discharge current and voltage. Taking an average over the experimental discharge power of the SPT-100, an improvement of 30% in anode efficiency, 15% in thrust and 13% in specific impulse is obtained for the most optimum configuration of frequency and voltage (ƒRF = 450 MHz, VRF = 10V). |
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