Model for Steady-State Fully Kinetic Ion Beam Neutralization Studies

Fully kinetic plasma simulations, in which ions and electrons are represented by computational particles, are attractive for modeling electron-ion coupling in spacecraft electric propulsion devices. While conceptually simple, fully kinetic simulations are susceptible to a numerical instability due to a finite computational domain. The widely utilized workaround is to artificially expand the domain and stop the simulation long before the plume reaches the mesh boundaries. The simulation thus never reaches the steady state, and massive computational resources are required. This paper describes a new boundary treatment for fully kinetic studies that allows reaching steady state on a relatively small domain. This approach is demonstrated by first modeling a preneutralized beam. The fully kinetic results are compared with a hybrid model with fluid like electrons. A more complex setup containing a centrally mounted cathode is investigated next. Grid independence is verified by comparing results on two different sized domains.