Thruster Performance Related to Plasma Mode-Transition and Plasma Hysteresis in Microwave Discharge Ion Thruster

Abstract

In microwave discharge ion thrusters, the plasma mode transition and hysteresis are two of the most important phenomena. The plasma mode-transition restricts the maximum thrust, whereas the hysteresis splits two mode of thrust in each flow rate. The previous thruster development and optical measurement indicates that there are two important parameters; the volume of magnetic confinement region where electrons are continuously heated by ECR and confined by magnetic mirrors, and waveguide plasma conditions. In this study, several kinds of thrusters that have different volume of magnetic confinement were tested. In addition, the enhancement of cut-off density inside the waveguide using larger diameter of waveguide was proposed. Experimental results show that the volume of magnetic confinement region is a key parameter for determining the maximum thrust. It was also found that the enhancement of cut-off is effective to eliminate the plasma hysteresis, whereas it does not affect the plasma mode transition. Hence, to further improve the thrust, one possible solution is to enhance the cut-off density at downstream of waveguide outside of magnetic field confinement region.