Laser-Induced Fluorescence of Neutral Xenon in the Near Field of a 200 W Hall Thruster

Abstract

Abstract : This work presents measurements of neutral xenon velocity in the plume of the Busek Company BHT-200-X3 200 W Hall thruster at a single 250 V anode potential operating condition. The xenon velocities were measured using laser induced fluorescence of the 6s'1/20/1 -6p'3/22 excited state transition at 834.68 nm. Velocities were interrogated near the exit plane of the anode discharge and in the vicinity of the cathode. Both axial and radial velocities were measured simultaneously using phase sensitive detection. The exit plane axial velocity varies from 350-50 m/s near the outer acceleration channel radius to approximately 150 m/s at the inner radius. The radial velocity at the outer insulator is approximately zero, but increases to approximately 100 m/s directed away from the protruding central magnetic pole at the inner insulator. This is consistent with the creation of neutrals at the inner radius by ions neutralized following a wall collision with the protruding central magnetic pole. Neutral velocities downstream of the exit plane also show a radial velocity away from the central magnetic pole. However, this behavior may be due to the influence of the cathode plume. Velocity measurements in the cathode plume show that xenon velocities reach in excess of 610 m/s. Since the cathode flow represents a substantial portion of the thruster flow and is only weakly ionized, the cathode plume may influence the neutral velocities nearer the anode. Evidence of interaction between the two flows takes the form of widened fluorescence line profiles which may indicate the collisional mixing disparate neutral streams or possibly several gas dynamic shocks.