Chemistry of low-pressure iodine plasmas

Since a few years, Xenon which is commonly used as propellant for electric propulsion applications becomes resource-critical. Among the potential alternatives to xenon, iodine could play a key role in the coming years. However, the chemistry of iodine plasmas is much more complex than the one of Xenon with excited molecules and atoms, atomic and molecular positive and negative ions and electrons. At LPP, since a few years, low-pressure iodine plasmas in conditions relevant for electric propulsion applications have been studied experimentally by combining different electrical and optical diagnostics. To compare with these experimental data, a global model and a particle-in-cell code have been developed to simulate low-pressure iodine plasmas. For both modeling approaches, the key part is the set of reactions and cross sections. In this work, we present and discuss the current reaction set for low-pressure iodine plasmas. First, we carry out a comparison with the reaction sets of two other gases which have been studied for many years: chlorine and oxygen. Second, we use the comparison with experiments in low-pressure iodine plasmas to identify key processes in the current reaction set of iodine that need to be further investigated.