Electron Detachment in Magnetic Nozzles

Magnetic nozzles help accelerate plasma in advanced electrodeless propulsion systems, a type of spacecraft propulsion that works without physical electrodes. Their performance depends critically on the interaction between plasma expansion and magnetic detachment, which remains insufficiently understood. Here we investigate plasma detachment in a diverging magnetic nozzle coupled to a Vacuum Arc Thruster by combining laboratory diagnostics with numerical modeling. Experiments employ Langmuir probe voltage sweeps to quantify electron backflow and density variations under different magnetic field strengths. Complementarily, Particle-in-Cell simulations with a fully kinetic solver and Boris particle pusher are used to resolve self-consistent velocity distribution functions in the imposed static magnetic field. Results show electron confinement and backflow suppression, and highlight the role of magnetic topology in determining detachment efficiency. Laboratory Langmuir probe measurements and PIC simulations consistently show that a 30mT magnetic nozzle suppresses upstream electron transport and reshapes the plume without increasing ion exhaust velocity. Performance improvements arise primarily from higher discharge voltage, while the magnetic field chiefly alters electron confinement and plasma distribution.