Collisional radiative model based investigation on the color appearance of xenon plasma in Hall thruster plumes

Abstract Hall thruster is a type of electric propulsion system used for spacecraft. The study of the Hall thruster plume, which is a plasma, reveals the thruster’s performance. Images of Hall thruster operating can be found from various online sources, the thruster plumes are typically transparent with a slight blue or green hue. However, some plumes are colorful instead of being monochromatic, with distinguishable regions. In this study, we investigated the xenon plasma color using a collisional radiative model and explained the color appearance of Hall thruster plumes. We show that xenon atoms and ions appear in different colors. For a standard observer, singly charged xenon ions appear in green, irrespective of the plasma environment. Xenon atoms, on the other hand, can appear blue, violet, or magenta. Through the investigation, we found that the resulting plasma color is related to the mass utilization efficiency and ion velocity of the thruster plume. We introduce an approach to produce color from collisional radiative models, where we use color as a property of the plasma, and demonstrate its usefulness for plasma studies.