Cathode Coupling Physics in a Hall Thruster

A rigorous investigation using advanced computer simulation of cathode plume in a Hall-effect thruster (HET) is proposed to improve fundamental understanding of cathode coupling and electron transport physics that strongly affect the performance and lifetime of a HET. The main research effort focuses on improving the current model to be more physics-based model, specifically by applying physically accurate boundary conditions i.e., cathode inflow and sheath-edge on walls, and including the magnetic field effects in the plume. The plasma plume generated by a 6-kW laboratory Hall thruster and central-mounted hollow cathode is simulated using a two-dimensional axi-symmetric hybrid particle-fluid model. The particle-based kinetic approach describes the heavy species, i.e., xenon ions and neutrals, while a detailed fluid model solves the continuity, momentum, and energy conservation equations of the electrons at steady state. To estimate the erosion rates on any walls, a sputtering model is implemented and applied to estimate the erosion rates along the cathode keeper wall. For the results published so far, the electron model neglected the magnetic field effect in the plume, which resulted in over-estimated plasma potential and electron temperature in comparison to measured data. Therefore, an improved electron model has recently been developed, tested, and implemented to the current code. The new electron model has a capability to simulate electron transport across a complex magnetic field topology in the plume, which includes a magnetic field separatrix and a purely axial component along the cathode centerline axis and a purely radial component near the discharge channel exit of the thruster.