Global model of a radio-frequency ion thruster based on a holistic treatment of electron and ion density profiles

Abstract

We present a global model of a radio-frequency ion thruster. The model takes into account radial and axial density distributions for electrons and ions of the plasma inside the ionization vessel. These spatial distributions are based on analytical equations and heuristic assumptions and are used self-consistently in all conservation equations. They are considered in the 3D computation of electromagnetic fields and used to calculate the induced power generated by the coil current. We also consider the spatial ionization and excitation inside the plasma volume in the context of energy and charge conservation. Furthermore, the model includes effects of local charge and power losses on the walls. The extraction grid system is modeled in detail describing each extraction channel separately. The spatial dependence of the electron and ion density profile also leads to a radially varying ion beam current and ion focus across the grid system. Therefore, the parameters of each beamlet differ and need to be described individually by the 3D ion extraction code. An extension of the extraction code also simulates the neutral gas transmission coefficient of the aperture system. This approach enables us to determine the neutral gas density inside the ionization vessel as well as the neutral gas losses. The peripheral electric losses in the coil, the RF cables and the radio-frequency generator are derived by a circuit model.