Numerical analysis of RF discharge in a nonuniform magnetic field

The radio-frequency (RF) plasma thruster has been studied to overcome the issue of a reduced lifetime of plasma thrusters due to electrode erosion, and it has been reported that a nonuniform magnetic field near the RF antenna improves the thrust performance. In this study, to obtain knowledge for optimizing the configuration of the thruster and the magnetic field, the RF discharge in a nonuniform magnetic field is numerically investigated focusing on RF power absorption and plasma generation, and the effect of the positional relation between the magnetic cusp and the RF antenna on the RF discharge is discussed. We adopt the two-fluid plasma model considering ions and electrons and confirm the qualitative validity of the simulation by comparing the simulation results with the results of a laboratory experiment. The simulation reveals that the energy transport due to the $Ey×B$ drift from the region of RF power absorption near the RF antenna determines the distributions of the plasma generation and temperature. Therefore, the plasma distribution changes depending on the RF antenna position and the phase of the RF period because the $Ey×B$ drift direction changes depending on the directions of the electric and magnetic fields. In addition, we find that it is important to place the antenna in a strong magnetic field for effective power absorption because this increases the azimuthal diamagnetic current.