Development and validation of iodine plasma models for electric propulsion systems

Iodine has emerged as an attractive alternative propellant to xenon for electric propulsion systems due to its significantly lower cost and its ability to be stored unpressurized as a solid. However, iodine plasmas exhibit more complex reaction processes and have additional energy-loss pathways, such as molecular dissociation, that complicate the development of theoretical or numerical plasma models. This is further exacerbated by the lack of reliable iodine electron-neutral collision cross-sections and experimental thruster performance data within the literature. Here we present a new iodine plasma model based on recently available collision cross-sections, and we perform a detailed comparison with experimental data from an iodine-fuelled gridded ion thruster. The model and experiment are in good agreement over a wide range of operating conditions and additionally show that the use of iodine can lead to a performance enhancement when compared with xenon. The results confirm the validity of the iodine reaction set used within the model which is not only relevant to electric propulsion systems, but also low-pressure iodine plasmas used in other applications.