Simulation of Vacuum Chamber Pressure Distributions with Uncertainty Quantification

One of the primary challenges in understanding variations in electric propulsion performance between ground tests and space operations lies in the pressure distribution within the test vacuum chamber. The chamber backpressure is much higher than experienced in space, modifying thruster performance and plume dynamics. Numerical simulation is a key element in determining the background conditions in nonideal vacuum chamber environments. An important parameter for the accurate simulation of chamber backpressure is the sticking coefficient, which sets the probability that an atom will stick to a cryogenic panel used to pump away the plume gases. This quantity can be used to model vacuum pumps in particle-based kinetic numerical methods. In this work, a three-dimensional direct simulation Monte Carlo code is used to model neutral xenon atoms flowing from the anode of the H9 Hall effect thruster within a large vacuum test facility. Simulated pressures are compared with ion gauge pressure measurements to infer the effective sticking coefficient of the chamber’s vacuum pumps. A pressure-predicting surrogate model is developed for inference of pump sticking coefficients and for uncertainty quantification. This information facilitates accurate and useful kinetic simulations of electric propulsion thruster plasma plumes in vacuum chambers.