  Gridded ion thrusters are tested in ground vacuum chambers to verify their
performance when deployed in space. However, the presence of high background
pressure and conductive walls in the chamber leads to facility effects that
increase uncertainty in the performance of the thruster in space. To address
this issue, this study utilizes a fully kinetic simulation to investigate the
facility effects on the thruster plume. The in-chamber condition shows a
downstream neutral particle density 100 times larger than the in-space case due
to ion neutralization at the wall and limited vacuum pump capability, resulting
in a significant difference in the density and distribution of charge-exchange
ions. The flux, energy, and angle of charge-exchange ions incident on the
chamber wall are found to be altered by the electron sheath, which can only be
simulated by the fully kinetic approach, as opposed to the conventionally used
quasi-neutral Boltzmann approach. We also examine the effect of backsputtering,
another important facility effect, and find that it does not necessarily
require a fully kinetic simulation as the incident flux and energy of the
sampled charge-exchange ion are negligibly small. Finally, we demonstrate that
the carbon deposition rate on the thruster is significantly influenced by the
angular dependence of the sputtered carbon, with a nearly 50% effect.
