Iodine plasmas for space propulsion and industrial applications

With as many as 2000 satellites per year forecast to be launched over the next decade, onboard propulsion systems will become increasingly important for ensuring both mission success and a sustainable space environment. Plasma-based electric propulsion systems are particularly attractive because of their high fuel efficiency, but due to challenges with conventional propellants such as xenon, a strong interest in viable alternatives has emerged. One such alternative is iodine, which in addition to space-based applications, is also of use in a number of ground-based industrial applications such as plasma etching. With a lower cost, higher global production output, and a reduced ionization threshold compared with xenon, iodine has the potential to meet current and future space industry demand while also providing improved propulsion performance. Furthermore, iodine is a solid at typical ambient conditions with a high storage density. However, iodine is chemically reactive with many common materials and has a more complex plasma chemistry that includes molecular dissociation, attachment to form negative ions, and several ionization processes creating positive atomic and molecular ions. This topical review provides a comprehensive overview of iodine within the context of plasma applications and also serves as a useful data source for various thermodynamic properties, collision cross-sections, and iodine-surface interactions. In addition to discussing the physical and atomic/molecular properties of iodine, we also highlight important theoretical, numerical, and experimental work in the field and discuss the current state-of-the-art: including the space flight heritage of iodine-fueled propulsion systems and remaining research/technical challenges.