Modeling complex plasma chemistry for electric propulsion in a hybrid simulation code

The chemistry of the low-temperature plasma discharge in electric propulsion devices is introduced for atomic and diatomic substances, and the related reactions are implemented in a particle/fluid multi-dimensional simulation code. For atomic substances: elastic, excitation and ionization collisions are considered. Excitation and de-excitation to and from metastable states can be state-selective, and thus it is possible to model stepwise ionization. For diatomic substances: in addition, vibrational and rotational excitations, dissociation and dissociative ionization are considered. Chemistry of the wall interaction is also modeled considering ion recombination, associative wall recombination, and the wall accommodation processes. Applications to two cases of interest are shown for an electrodeless plasma thruster. First, the effects of the stepwise ionization from metastable states operating with Xe are analyzed. Simulations are run for several operation conditions (on mass flow and electric power) to find regimes where stepwise ionization is important, and how it impacts on the plasma response. Second, the air-breathing concept is assessed. Simulations are run with air substances (nitrogen and oxygen) for various operation conditions to find the best thrust efficiency, and the plasma discharge characteristics and thruster performances obtained are compared with those of Xe.