Effects Of Wall Material On Radial Plasma Flow Of Hall Thrusters

Hall Thruster is a widely used electric propulsion device. Its structure is very simple but operational mechanism is very complicated. The theory of how it works is far from being completely understood. The dielectric wall whose characteristics have been proved to have a remarkable influence on Hall Thruster's performance is one of the most important components of Hall Thruster. But actually the physics of plasma interaction with the wall and the transition between quasi-neutral plasma and sheath has not been investigated in detail.In order to study influence of different materials on the performance of Hall Thruster, the plasma-wall transition model was built to investigate the relations between different parameters with interactions between plasma and wall. In order to focus on the object, the direction normal to the wall was considered. The plasma parameters were thought to be uniform in other directions. Two types of model were used separately to achieve the results. They were presheath-sheath model (separate model) and total model. In the presheath-sheath model the transition between plasma and wall was separated into two parts, i.e. presheath and sheath. The two parts were connected by making use of boundary conditions.The total model treated the transition as a whole. Results showed that the two types of model were in accordance with each other. The plasma-wall transition model served to guide the analysis of the interaction between plasma and wall. For the purpose of verifying whether the results of plasma-wall transition model could be used in Hall Thruster and applying the performance analysis in an actual Hall Thruster, a two dimensional model of Hall Thruster was developed. Axial and radial directions were considered. Only presheath region was considered in the model. Ions and elections were treated as fluids. A magnetic field with only a radial component was imposed. The basic equations were developed from theory of Computational Fluid Dynamics (CFD). Steady-state results were obtained by Newton Interaction method.Linking the results analyzed from plasma-wall transition model with the actual results from Hall Thruster model, we obtain that the potential drop of presheah and sheath and the ion flux to the wall are decreasing with secondary electron emission (SEE) coefficient increased. Based on this result and by means of computation and theoretical analysis, we come to the conclusion that with higher SEE coefficient, there will be less corrosion on the dielectric wall, divergence angle of flume will be smaller and higher efficiency of Hall Thruster can be achieved. The computational and analyzing results are in accordance with the experimental data attained by others.