Development and implementation of a plasma chemistry model for Helicon Plasma Thruster analysis

The present work is part of a wider project aimed at improving the description of the plasma dynamics during the production phase of a Helicon Plasma Thruster. In particular, the work was focused on the development of a chemical model for Argon and Xenon based plasma. The developed model consists of a collisional-radiative model suitable to describe the dynamics of the 1s and 2p excited levels (Paschen notation). The model is meant to be complementary to 3D-VIRTUS, a numerical tool developed by the University of Padova in order to analyse helicon discharges. Once identified the significant reactions for both propellants the reaction rate coefficients have been integrated exploiting cross-sections from literature and assuming a Maxwellian velocity distribution function for all the species. These coefficients have been validated against experimental measurements of an Argon helicon discharge and compared with a well established code. The validation served also to identify the optimal database of cross sections of excitation reactions, among those available in literature for the Argon chemical model. The reactions given by the identified optimal database have been subsequently reduced through a proposed lumping methodology. In this way, it was possible to reduce the number of equations of the system to solve, and implement them into 3D-VIRTUS. A validation against an experimental case taken from literature has been performed, showing good agreement of the results. Regarding the Xenon model, only a verification has been done, against the results of another collisional-radiative model in literature. Finally, a predictive analysis of the propulsive performances of a Helicon Plasma Thruster for both Argon and Xenon is presented.