Compositions and distributions of the azimuthal currents in the magnetic nozzle

The azimuthal currents in the divergent magnetic nozzle of the electrodeless plasma thrusters are investigated using a two-dimensional axisymmetric particle-in-cell (PIC) code. In this paper, the azimuthal currents are decomposed into four components -- the diamagnetic drift current, the E×B drift current, the viscous-stress-induced current and the inertia-induced current. The azimuthal current and its four components are analyzed under three magnetization levels of 0.25 T, 0.75 T and 2.15 T. In the absence of inlet ion temperature, the azimuthal currents mainly consist of electron currents resulted from ∇pe, E×B drift and electron viscosity, while the azimuthal currents caused by the inertia can generally be neglected. The azimuthal ion currents considered negligible in previous studies are shown to be non-negligible in the highly-magnetized and collisionless magnetic nozzle, where the dominant mechanism for its formation is E×B drift and drift from the centrifugal force. In the upstream and midstream, the compositions and distributions of the azimuthal currents can vary at different radial positions and magnetization conditions because of the influence of the electric potential barrier and the high density conic. In the downstream, a vast range of paramagnetic currents are produced by the E×B drift due to ion inward detachment. And the paramagnetic stress-induced current begins to prevail due to the FELR effect. Superimposed with the paramagnetic part of the diamagnetic drift current under a high magnetic field, they can undermine the thrust gain coefficient of the magnetic nozzle.