Recent laboratory experiments on radiofrequency plasmas in magnetic nozzles

Convergent and divergent magnetic field configurations, commonly referred to as magnetic nozzles, give rise to a variety of plasma processes, including plasma generation, acceleration, momentum and energy transfer, wave excitation, and cross-field transport. Such processes are of fundamental importance in plasma physics and underpin spacecraft electric propulsion technologies. In recent years, radio frequency (RF) plasma sources combined with magnetic nozzles have attracted considerable attention as electrodeless plasma propulsion systems. Despite their relatively simple configuration, consisting primarily of a RF plasma source and a magnetic nozzle, the plasma dynamics involve complex phenomena. Understanding these phenomena is essential for both elucidating the physics of magnetically expanding plasmas and improving the performance of magnetic-nozzle plasma thrusters. This article reviews recent experimental progress in the understanding of RF plasmas in magnetic nozzles, with particular emphasis on the fundamental plasma processes relevant to spacecraft propulsion.