NOVEL COUPLING METHODS FOR FLUID AND KINETIC SOLVERS IN THE NUMERICAL MODELING OF HELICON PLASMA THRUSTERS

To allow the self-consistent modelling of plasma transport throughout the multiple flow regimes encountered inside Helicon Plasma Thrusters (HPTs) and other magnetically enhanced plasma thrusters, a coupled model is developed. The resulting model, MUPETS (MUlti-regime Plasma Equilibrium Transport Solver), is based on the self-consistent coupling between fluid and Particle-In-Cell (PIC) solvers and can be applied to the full domain of a plasma thruster and it's surrounding space. Running the fluid and kinetic solvers iteratively, found solutions are passed from each model to the other, thus eliminating the need for assumptions on the boundary conditions at the interface between the numerical domains. To achieve this both the boundary conditions as well as the numerical domains are coupled self-consistently. From the fluid model the plasma species' solved properties are coupled to the species' particle distribution function (PDF) and velocity distribution function (VDF) injected in the kinetic model. Meanwhile the solved gradient of the plasma potential ϕ in the kinetic model is coupled back to that of the fluid model. The numerical domains are distributed to match the respective fluid and kinetic regimes occurring in the thruster, with the plasma inside the source chamber assumed to be in the fluid regime, the plasma exhaust in the magnetic nozzle to be in the kinetic regime, and the interface to be at the thruster's throat at the outlet of the source chamber. The coupled model has been tested for a simulated thruster operating on Argon at 50 W input power and 0.05 T magnetic field strength. The resulting plasma profiles converge within the first 2 iterations of the coupled model. At the coupled model's domain interface, the average densities of the ions and electrons differ less than 1% and 4% between the fluid and kinetic models.