Sticking Coefficient Effects on the Carbon Deposition Rates in an Electric Propulsion Testing Chamber

Ground testing is essential for understanding carbon sputtering caused by interactions between thruster beam ions and chamber walls. These interactions lead to back-sputtered carbon particles, which can contaminate the thruster. This study employs kinetic simulations with two distinct sputter models to analyze the deposition rate of back-sputtered carbon at the thruster exit. Previous studies have shown that yield models and angular distributions significantly influence sputtering behavior, often without considering the effects of sticking coefficients. In this work, we emphasize the role of energy distribution in determining deposition rates. Sticking coefficients, derived from molecular dynamics simulations as functions of incident energy and angle, are incorporated through post-processing the numerical results. While sticking coefficients from two different models are similar at normal incidence, our findings highlight a critical difference at high angles of incidence, we found that the Sigmund- Thompson energy distribution results in lower sticking coefficients compared to those derived from molecular dynamics based energy distributions. This discrepancy indicates that in future full chamber simulations using MD-based sticking coefficients, secondary carbon emissions from the sidewalls are likely to influence the deposition rate on the thruster.