Numerical investigation of antenna position effect on thrust of a radio-frequency plasma thruster with a magnetic cusp

Radio-frequency (RF) plasma thrusters have been proposed to overcome thruster lifetime limitation due to electrode erosion, and using a magnetic cusp has been reported to improve thrust performance. It has been reported that an RF plasma thruster with a magnetic cusp has an optimal antenna position for achieving maximum thrust. However, the detailed mechanism by which the antenna position contributes to the thrust has not yet been clarified. This study analyses the effect of antenna position on plasma characteristics and thrust in an RF plasma thruster with a magnetic cusp to clarify the mechanism that determines the antenna position for maximum thrust using a numerical simulation. Simulations of the entire thruster system using a two-fluid plasma model with ions and electrons show that the electrical potential profile of an RF plasma thruster with a magnetic cusp varies significantly during one RF period. This is due to the electron transport. The direction of electron transport is determined by that of Eθeθ×B drift, which is caused by the azimuthal electric field driven by the RF antenna and the externally applied magnetic field. We further found that the optimum antenna position should satisfy the following two conditions: (1) be near the cusp and (2) be near the discharge chamber outlet. Finally, our simulation results were validated against experimental results.