A fully kinetic study on the plasma detachment processes in the collisionless propulsive magnetic nozzle

Abstract

A fully kinetic axisymmetric particle-in-cell model is employed to simulate and study the detachment processes of electrons in the propulsive magnetic nozzle. The detachment ratio is adopted to evaluate the extent to which the electrons detach from the magnetic field. The theoretical expression for the electron detachment ratio is derived and indicates that the electron detachment is driven by two mechanisms: inertia effect and gyro-viscous effect. The simulation results show that the detachment direction of electrons are outward in the upstream and inward in the downstream. In addition, the dominating detachment mechanisms in the upstream is inertia effect, while the gyro-viscous effect is equally, if not more, important as the inertia effect in the downstream, especially around the periphery of the magnetic nozzle under lower magnetic field strength. Moreover, the electron detachment is found to contribute to no more than 20% of the axial flux of plasma in the downstream, while the majority of it is caused by the electrons flowing along the magnetic field.