Simulations of Ion Thruster Beam Neutralization Using a Particle–Particle Model

Abstract

A particle–particle (PP) model is developed to simulate ion thruster beam neutralization by thermal electrons emitted from a neutralizer located outside of the ion beam. Simulations are carried out using the real xenon to electron mass ratio. The results show that beam neutralization is initiated by an electron–ion mixing process in which the thermal electrons are trapped by the potential well in the ion beam and undergo an oscillation between the ion beam boundaries both along the beam direction and in the radial direction. The bouncing of the electrons in the radial direction generates transient oscillating perturbations inside the beam in both electron density and the electric field in the radial direction, which eventually dissipate when the electrons are thermalized and the ion beam is neutralized. The PP method directly uses Coulomb’s law to calculate the electrostatic force between particles and thus eliminates the constraints on mesh resolution and domain size of the particle-in-cell method. This method can be advantageous computationally when applied to simulations of very nonuniform, collisionless plasmas such as the plasma plume near ion thruster exit.