Causality analysis of vacuum chamber facility effects for Hall effect thruster operation

Abstract

Characterization of plasma dynamics is critical for controlling electric propulsion systems on spacecraft. Understanding the causal relations between measurement data can play an important role both in minimizing the number of diagnostics and in informing which dynamic information needs to be accounted for in a computational model. In this paper, we apply extended convergent cross mapping (eCCM) to three measured telemetry signals—cathode current, discharge voltage, and cathode-to-ground voltage—collected from a krypton-fed magnetically shielded Hall-effect thruster with base operating pressures of 6.8 and 8.5 μTorr at the 4.5 and 6 kW power levels, respectively. Data were also collected at elevated pressures, two to three times the base operating pressure. We discuss the sensitivity of the cross-mapping skill to the embedding parameters and background pressure in the vacuum chamber. We propose eCCM as a framework for characterizing dynamic relationships in the Hall-effect thruster circuit, guiding the selection of signals and the prioritization of dynamic measurements in subsequent physics-based modeling and diagnostic efforts. The results show that cross-mapping skill decreases across nearly all signal pairs for both power levels, indicating a reduction in mutual dynamic information between electrical circuit components as background pressure increases. The analysis suggests that the discharge plasma is coupled to other unmeasured components in the system as the facility pressure varies.