Numerical simulation of a helicon plasma thruster production stage

The purpose of this thesis project is to accurately simulate the plasma transport in the production stage of a Radio Frequency (RF) thruster. A plasma can be defined as an ionized gas made of different species that show a collective behaviour. Species involved are electrons, ions, neutrals at ground state and neutrals at the excited state, which are simulated by means of a fluid approach. The choice is justified given that the Knudsen number in the discharge is in the continuum regime. The numerical tool used has been developed inside the Alma Propulsion Laboratory of the University of Bologna based on the openFOAM C++ libraries that make use of the Finite Volume Method for the PDE resolution. The code encompasses the full set of fluid momentum, continuity and energy conservation equations for heavy species (i.e., ions and neutrals). Whereas for electrons the Drift Diffusion (DD) approximation is used, the results have been an acceptable approximation for this species. A semi-implicit method is used to solve the electric field via the Poisson’s equation. The most critical phase in the simulation process was the definition of boundary conditions. Firstly, only neutrals, under the assumption of isotherm flow, have been simulated employing several combinations of physical conditions for the velocity and the density. Then the charged species have been introduced, simulating ions, excited neutrals species, and electrons with the DD model. To this end, a proper set of boundary conditions for charged, excited species, and electric potential have been introduced.