Laser-Induced Fluorescence of Singly-Charged Xenon in a 6-kW Hall Thruster Plume

We present laser-induced fluorescence velocimetry measurements of the 5d[4]7/2 → 6p[3]5/2 transition for singly-charged xenon (Xe II) at 834.953 nm (vacuum) in the near-field plume of a 6-kW Hall thruster. Axial velocity profiles were obtained at six locations axially along the channel centerline and nine locations radially across the thruster channel at the exit plane. Discharge voltage was maintained at 300 V, and the anode mass flow rate was set to 5, 10, and 20 mg/s, corresponding to steady-state power levels of 1.5, 3, and 6 kW. Since no published hyperfine structure constants were available for this transition, we used intermodulated optogalvanic spectroscopy to obtain an approximate lineshape for deconvolution of raw data. The acceleration zone was found to be on the order of few tens of millimeters in length. The loss voltage decreased from 45 V to 26 V as the mass flow rate was increased from 5 to 20 mg/s. The bulk axial velocity at the exit plane peaked near the channel walls for all operating conditions. The axial velocity distribution along the thruster centerline exhibited a high-velocity tail, which may be due to charge-exchange effects. A lowvelocity tail was observed for near-wall velocity profiles.