Nonintrusive characterization of the azimuthal drift current in a coaxial ExB discharge plasma.

A diagnostic is developed for the nonintrusive study of the azimuthal drift current in the coaxial ExB discharge of a Hall plasma accelerator. The technique of fast current interruption is used to generate a signal on several loop antenna that circle the outer wall of the discharge channel. The signal on the antenna is recorded, and used to determine the spatial distribution of the azimuthal drift at the moment of current interruption. The results of the experiment are compared to estimates derived via prior intrusive measurements, and the intrusive estimates are found to predict the spatial characteristics of the azimuthal drift, but underestimate its total magnitude. The self-induced magnetic field is then calculated and added to the applied magnetic field. The peak total magnetic field is seen to shift 2-5mm towards the anode due to self-induction, and suffer a reduction in magnitude of 10%-15%. The peak in the total magnetic field is then found to more closely coincide with the peak of the measured electric field than the peak of the vacuum magnetic field. It is concluded that the self-induced magnetic field could be important to anomalous electron mobility in the Hall-effect thruster, and simulation efforts should try to include its impact.