Internal plasma potential profiles in a laboratory-model Hall thruster

The Plasmadynamics and Electric Propulsion Laboratory High-speed Axial Reci procating Probe system is used in conjunction with a floating emissive prob e to measure plasma potential in the discharge chamber of the P5 Hall thrus ter. Plasma potential measurements are made at a constant voltage, 300 V, a t two different discharge current conditions: 5.4 and 10 A. The plasma pote ntial contours for the 5.4 A case indicate that the acceleration region beg ins several millimeters upstream of the exit plane, extends several centime ters downstream, and is uniform across the width of the discharge chamber. The 10 A case is similar to the 5.4 A case with the exception that the acce leration region is shifted downstream on centerline. Axial electric field p rofiles, computed from the measured potential, show a double peak structure in the 5.4 A case, indicating a zone of ion deceleration. Perturbations to the discharge current are shown to correspond spatially with the location of the peak electric field indicating that thruster perturbations may resul t from a disturbance to the Hall current, as opposed to ablation of probe m aterial. This conclusion is supported by the lack of any observable materia l ablation. (C) 2001 American Institute of Physics.