Self-Neutralizing Characteristics of Ion Optics Using RF Self-Bias Effect

Traditional ion thrusters extract ions from a plasma source by applying a DC voltage across the ion optics. A separate electron-emitting neutralizer is required to ensure the quasi-neutrality of the downstream plasma and to prevent the accumulation of ion space charges in the plume. If instead a radio-frequency (RF) voltage is applied across the ion optics, ions and electrons can be extracted from the plasma source alternatively and the neutralizer could be absent. This can reduce the lifetime limiting factor of the ion thruster. Using a combination of theory and particle-in-cell simulations, the self-neutralizing characteristics of the ion thruster have been evaluated by calculating the downstream potential of ion optics. The effect of the radio frequency, grids aperture parameters, grids voltages and gas species (argon, krypton and xenon) on the self-neutralizing characteristics is systematically investigated. It is found that there is an optimal radio frequency to guarantee the minimum downstream potential of ion optics. The dependences of the optimal radio frequency on the grids structural and voltage parameters have been determined for different gas species. The results of present work are of substantial importance for indicating the selection of the operating parameters of RF self-bias ion engines.