Global model of a radio-frequency iodine neutralizer

Abstract Iodine is an attractive emerging alternative propellant to xenon because of its lower cost, higher global production output, lower ionization threshold, and its ability to be stored unpressurized as a solid. In some electric propulsion systems, such as gridded ion thrusters, electron-emitting neutralizers are a critical component needed for maintaining current balance and preventing spacecraft charging. This work presents a comprehensive global model of a radio-frequency (RF) neutralizer operating with iodine. The model includes over 100 reaction processes and tracks 8 separate particle species while also accounting for RF electromagnetic coupling and plasma-gas heating of atomic and molecular iodine. Model results are compared with existing experimental data for a low-power (approximately 50 W) RF neutralizer where good agreement is observed for important performance metrics such as neutralizer current, electron energy cost, and gas utilization efficiency. Iodine gives comparable, if not superior, performance to that of xenon at low mass flow rates, below about 10 μ g s − 1 , demonstrating its viability as an alternative propellant. A detailed analysis of power loss channels shows that RF coil losses, wall losses, and excitation to the first excited state of atomic iodine are the dominant loss processes. Efficient neutralizer operation therefore requires careful design to ensure that the electron temperature is sufficiently high (above about 4 eV) to favor ionization reactions, but sufficiently low to minimize the wall sheath potential.