Plasma coupling mode transition in a low-power decoupled magnetic nozzle device

This study investigates the effects of varying input power on plasma topology in a radio frequency device with a magnetic nozzle. To this end, an experimental campaign was conducted, spanning through five different power levels, from 100 to 400 W. Two dimensional profiles of plasma potential, floating potential, ion saturation current, and ion energy distribution function were collected both in the source and in the expansion chamber. The measurements revealed a significant change in plasma behaviour at low power, whereas higher power cases showed a similar trend. From the analysis of the plasma density under the antenna, an E to H coupling mode transition between 100 and 200 W was hypothesised, which correlates well with the more pronounced influence of the electromagnetic fields on the plasma bulk at low power.