Numerical study of positive column plasmas in iodine and xenon: The impact of negative ions

The paper presents the results of a computational investigation comparing properties of xenon and iodine low-temperature plasmas under conditions relevant to gas-discharge neutralizers used in plasma propulsion technologies. A 1D self-consistent numerical model based on the fluid approach with drift-diffusion approximation for charged particle fluxes was coupled with heat transfer equation to simulate a longitudinal positive column sustained by constant electric field. Simulations were performed for a pressure range of 10–550 Pa, tube radius of 1 cm, and discharge currents 0.5–5.0 A. The comparative analysis revealed significant differences between xenon and iodine discharge properties. While the electric fields required to sustain the specified current for iodine and xenon were comparable, gas temperatures were dramatically different—up to a factor of 6 greater for iodine. This substantial difference is attributed to increased Joule heating, resulting from high electronegativity and considerable ionic current, as well as to heating from electron-impact dissociation and dissociative attachment. The influence of wall sticking probability γwall of atomic iodine on electrical and thermal characteristics of iodine plasma is analyzed. It is shown that for the positive column, the use of materials with lower γwall can significantly reduce electronegativity, gas heating, and electric fields required to sustain the discharge.