Ion Velocity Measurements Within the Acceleration Channel of a Low-Power Hall Thruster

This paper presents axial ion velocity measurements within the acceleration channel of the 200-W Busek Company Inc. BHT-200 laboratory Hall thruster derived from laser-induced fluorescence measurements of the 5d[4]_7/2 - 6p[3]_5/2 xenon-ion excited-state transition. Acceleration-channel-centerline ion velocities were measured for one nominal and six related cases. These six cases were chosen to be representative of small variations of the applied propellant flow, magnetic field, and discharge potential from the nominal condition. These deviations in operating parameters translate into changes in the plasma density, electron transport, and applied electric field, respectively. The effect of varying the magnetic field, hence influencing the electron transport, is to adjust the location of the internal ion acceleration. Increasing the anode propellant flow, which proportionally increases the plasma density and also influences the electron transport, appears to shift the acceleration upstream. Increasing the discharge potential increases ion acceleration proportionally. Examinations of the fluorescence traces, which have been previously shown to be representative of the ion velocity distributions, are also undertaken. From these data, it is possible to estimate internal axial electric fields and identify regions of ion acceleration and creation.