The influence of adding Monte Carlo collisions on convergence in 3D PIC simulations of Hall thruster azimuthal instability

Abstract The anomalous electron transport mechanism induced by azimuthal instability remains a core unresolved physical issue in Hall thrusters. This instability involves complex non-equilibrium, nonlinear particle motion processes and is strongly coupled with the radial wall sheath and axial electric field acceleration, thus large-scale 3D PIC simulations are necessary to be conducted for higher accuracy studies. In previous PIC models for Hall thruster azimuthal instability, atom ionization has typically been approximated using a given analytic function, neglecting the self-consistent coupling between the ionization process and instability. In this paper, a 3D PIC model is developed based on 2D radial-azimuthal and axial-azimuthal benchmarks, with the Monte Carlo collision (MCC) ionization model replacing the analytic function approximation. This work aims to investigate the impact of applying the MCC model on simulation convergence in 3D PIC simulations of Hall thruster azimuthal instability. An appropriate neutral atom distribution is obtained through a number of 3D PIC-MCC test cases, and a modified cathode boundary is proposed to better maintain the steady state of the simulation.