Plasma properties conditioned by the magnetic throat location in a helicon plasma device

Measurements are taken using a helicon plasma device to analyze the spatial distribution of plasma properties as the throat of the magnetic nozzle is axially shifted with respect to the antenna center. Krypton plasma is generated in the sub-kilowatt range and probed using a suite of diagnostics including a rf-compensated Langmuir probe, a planar probe, and laser-induced fluorescence. It is found that larger ion currents and increased plasma confinement are achieved when the throat of the magnetic nozzle is located downstream the antenna center, at a distance that equals or exceeds two times the antenna length. The ions, although being accelerated, retain subsonic velocities even beyond the magnetic throat.