The effects of numerical acceleration techniques on PIC-MCC simulations of ion thrusters

The particle-in-cell-Monte Carlo collision method has been widely used in simulation studies of ion thrusters. Due to the huge computational demand of such simulations, numerical acceleration techniques are required. However, the effects of such numerical acceleration techniques on the simulation results are not clear. In this study, the effects of three numerical acceleration techniques are investigated using a series of simulations that implement different numerical acceleration factors. The resulting plasma potentials, plasma density distributions, and plasma currents in the discharge chamber are compared for simulations accelerated by increasing the vacuum permittivity, reducing the mass of heavy particles, and making use of self-similarity. The results demonstrate that increasing the permittivity thickens the sheath. When the sheath expands enough to extend to the cusps, the distributions of the potentials and the plasma densities are affected, influencing the current parameters. Reducing the masses of heavy particles greatly influences ion properties, especially the plasma density. Thus, it causes significant errors in the potential and current parameters. Errors in the beam current can be significantly decreased by correcting the beam current using an exponent relationship between the mass scaling factor and the plasma density. The use of self-similarity simultaneously thickens the sheath and decreases the particle number density and may slightly reduce the plasma current values. A number of suggestions for employing these techniques are also provided.