Kinetic, 3-D, PIC-DSMC Simulations of Ion Thruster Plumes and the Backflow Region

Three-dimensional, fully kinetic, coupled particle-in-cell direct simulation Monte Carlo (PIC-DSMC) simulations are performed to accurately predict the self-consistent electric field and plume and backflow characteristics of an ion thruster, and are compared with results based on the usual Boltzmann approximation. The fully kinetic calculations are performed for the first time using the operational thruster exit number densities without geometric scaling and the actual electron-to-ion mass ratio. It was found that kinetic treatment of both electrons and ions significantly affects the self-consistent radial electric field as well as the backflow ion characteristics. For the xenon ion plume with a colocated electron source, increase in the thruster exit number density strengthens the radial electric field which, in turn, increases the energy of the backflow ions by an order of magnitude. In addition, the spanwise variation of the ion flux on the solar panel showed that charge-exchange ions mostly impinge at the tip of the solar panel, furthest from the thruster geometry, for the fully kinetic cases. In comparison, the Boltzmann relation predicts a lower radial electric field for the operational high number density case, resulting in near-normal ion incidence angles in the backflow region causing significant flux closer to the thruster geometry.