The swirl acceleration mechanism in the propulsive magnetic nozzle

The study employed a fully kinetic axisymmetric particle-in-cell model to investigate the swirl acceleration mechanism in a propulsive magnetic nozzle. This work systematically examined the global transport process of plasma within the magnetic nozzle, encompassing both radial and axial transport processes. The investigation revealed a distinct ion-driven ambipolar transport mechanism in the magnetic nozzle, resulting from the magnetic field's suppression of electron cross-field transport. By establishing the plasma kinetic equation, the study elucidated the conversion pathway from ion swirl kinetic energy to ion axial kinetic energy within the nozzle. The swirl acceleration process was found to progress through three distinct stages: centrifugal motion, radial ion-driven ambipolar transport, and axial electron-driven ambipolar transport. In the nozzle's downstream region, the primary contribution of swirl acceleration to ion axial kinetic energy originated from the conversion of swirl kinetic energy into electromagnetic acceleration power driven by E×B drift. However, swirl motion was observed to induce unforeseen adverse effects such as diamagnetic drift attenuation and enhanced viscous loss in azimuthal current, leading to actual swirl-induced axial kinetic energy flux increments of approximately 38% (compared to the injected swirl kinetic energy flux) when the inlet swirl velocity is 1 Mach.