Cross-field electron transport induced by a rotating spoke in a cylindrical Hall thruster

Rotating spoke phenomena have been observed in a variety of Hall thruster and other E x B devices. It has been suggested that the spoke may be associated with the enhancement of the electron cross-field transport. In this paper, the current conducted across the magnetic field via a rotating spoke has been directly measured for the first time in the E x B discharge of a cylindrical Hall thruster. The spoke current was measured using a segmented anode. Synchronized measurements with a high speed camera and a four-segment anode allow observation of the current as a function of time and azimuthal position. Upwards of 50% of the total current is conducted through the spoke, which occupies a quarter of the Hall thruster channel area. To determine the transport mechanism, emissive and Langmuir probes were installed to measure fluctuating plasma potential, electron density, and temperature. A perturbed, azimuthal electric field and density are observed to oscillate in-phase with the rotating spoke. The resulting drift current is found to enhance electron transport with a magnitude equal to the spoke current to within margins of error. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3671920]