Electron dynamics of two magnetic nozzle geometries for a vacuum arc thruster

Electron dynamics in magnetically guided vacuum arc thruster plumes are critical to understanding both performance and spacecraft–plasma interactions in miniature electric propulsion systems. Changes in the space industry from high-cost large satellites to constellations of smaller satellites, motivates research into lightweight, low-power electric propulsion devices. Vacuum arc thrusters are assessed for their capability as miniature, high-specific-impulse alternatives to existing electric propulsion technologies for small satellites. We combine a vacuum arc thruster with permanent magnets around its nozzle to guide the plasma plume, and perform numerical simulations to evaluate the modified design. For a bismuth-fuelled thruster, we find that a straight magnetic nozzle increases thrust by ~ 25% compared with a no-magnet straight nozzle configuration, but promotes field-aligned electron transport and electron–ion separation within the near-field plume, which may be undesirable in terms of spacecraft plasma interactions. A diverging nozzle with permanent magnets reduces thrust by ~ 18% relative to a no-magnet diverging baseline, because the diverging field lines guide electrons radially outward and weaken the ambipolar axial acceleration. Despite this, the diverging nozzle better maintains electron–ion co-location, making it the more practically promising geometry from a spacecraft-interaction standpoint.