Characterization of Facility Effects on the Operation of a 20 kW Hall Thruster

In the last decade, the increasing interest of the space industry towards Hall Thruster technology has led to the need of studying the effects of the on-ground test environment so as to reliably predict the behavior of these thrusters when operating in space. Among the various facility effects that may alter the thruster performance, the background pressure inside the vacuum chamber is the most dominant one. Indeed, the ingestion of background neutrals has been demonstrated to increase the efficiency and the measured thrust, leading to performance levels different to the ones we would experience in the actual space environment. This effect is more evident with high power Hall Thrusters, due to the larger mass flow rates and, consequently, the higher background pressure levels achievable with the existing facilities. In this work, after a brief introduction on plasma propulsion and Hall Thruster technology, we provide an extensive overview of characterization tests carried out so far to investigate facility effects for several Hall Thrusters models. In the overview, together with performance levels, the effect of the chamber pressure on the discharge current oscillations and thruster plume are also presented. The following part is dedicated to the analysis of the data collected for the HT20k Hall Thruster operating in SITAEL’s IV10 vacuum chamber. The latter can operate at different pumping speeds, resulting in different background pressures levels for each selected operating point. The ion current density distribution in the thruster plume was then evaluated using state-of-the-art methods. The extensive parameters, such as the beam current and plume divergence were calculated for several operating points and then compared at various chamber pressures. In parallel to this, a novel approach, introduced in this work, was also adopted to calculate the extensive parameters of the plume and it was compared to the existing methods. In addition, an extrapolation to vacuum condition was also performed. Finally, the analysis of discharge current oscillations was also carried out. The study focused on the study of the main oscillation frequency and amplitudes as a function of the magnetic field peak and background pressure levels. The results were then compared to those available in literature, giving further insight on the impact of the testing environment on thruster performance