Rarefied Background Flow in a Vacuum Chamber Equipped with One-Sided Pumps

Abstract

Spacecraft propulsion systems, such as Hall thrusters, are designed and tested in large vacuum chambers. The pumping capacity of modern facilities makes it possible to maintain pressures as low as 10 −3 ‐10 −4 Pa with thrusters in operation. For these vacuum chambers, a fundamental concern is the facility effects on the chamber performance. Several free molecular models are proposed to analyze the rarefied background flow inside a vacuum chamber equipped with one-sided vacuum pumps located at one chamber end. These models lead to various sets of analytical expressions linking several facility effects, such as pump sticking coefficient, pump area, and wall effects. These expressions can be used to estimate the pump sticking coefficient, to evaluate performance of vacuum chambers, and to aid constructing proper background flow for particle simulations. About 70 numerical simulations of background flows inside a vacuum chamber validate these models. These numerical simulations and analytical results indicate that these models are capable of predicting average background pressure and flow velocities. Depending on specific parameters, the background flow can have a significant nonzero mean velocity and cannot be considered to follow a Maxwellian velocity distribution.