Current-Free Plasma Thruster Controlling Cross-Field Diffusion under a Magnetic Nozzle

Abstract

A radiofrequency plasma source having a magnetic nozzle is designed to investigate effects of cross-field diffusion on a helicon plasma thruster performance. The source consists of an insulator glass source tube, rf antenna, and a solenoid providing a rapidly diverging magnetic nozzle. These structures are immersed in a 60-cm-diameter and 140-cm-length vacuum chamber. The magnetic field strength can be increased up to ~900 Gauss while being maintained below 200 Gauss in the source tube. As the ion Larmour radius is comparable to or less than the source tube radius, it is expected that the field strength does not affect the plasma loss rate to the radial boundary and the resultant plasma production within the source. Measurement of the plasma density with a Langmuir probe demonstrates that the cross-field diffusion in the downstream magnetic nozzle is inhibited by increasing the magnetic field strength, while maintaining constant plasma production. The effect of the cross field diffusion on the thruster performance will also be presented.