Numerical investigation of plasma properties for the microwave discharge ion thruster μ10 using PIC-MCC simulation

Abstract

This paper reports the numerical investigation of plasma properties for the microwave discharge ion thruster μ10. The model consists of a particle in cell simulation and a Monte Carlo collision simulation. The results indicate that the plasma density and the electron temperature in the confined region are larger than those in other regions and are qualitatively consistent with probe measurements. Moreover, we traced the trajectories of charged particles to investigate the plasma generation and transport. The electron trajectories indicate that electrons are strongly confined by the mirror magnetic field and the sheath, which indicates that the confinement depends on the electron energy. As a result, the electron energy distribution function is a combination of two Maxwellian distributions. Although the hot electrons account for 3.4% of all electrons, they account for 50.1% of the ionization and can generate plasma with an excitation loss of 1/3 of that of cold electrons. The ion trajectories indicate that they are affected by the magnetic field. To investigate the effect of the magnetic field on the transport, we evaluate the ion and electron current percentage toward the wall and compare with the wall surface percentage. The ion and electron current ratios differ because of diffusion with respect to the magnetic field. The ion current percentage is larger than the surface area percentage in the grid, which indicates that ions are transported to the grid more efficiently due to the magnetic field. Therefore, the effect on ions by the magnetic field is one of the most important criteria for microwave discharge ion thrusters.