Microsoft Word - IEPC2009-087-InternalXEI v10.docx

We present laser-induced fluorescence velocimetry measurements obtained using the Xe I 6s[3/2]2 → 6p[3/2]2 transition at 823.4 nm (vacuum) and the Xe I 6s’[1/2]1 → 6p’[3/2]2 transition at 834.9 nm (vacuum) from the inside and in the near-field plume of a 6-kW Hall thruster. The thruster is operated under seven conditions with discharge voltages ranging from 150 to 600 V, and anode mass flow rates ranging from 10 to 30 mg/s. Axial sweeps along channel centerline are performed at each operating conditions. Radial sweeps at the exit plane are performed at the nominal condition. Velocimetry results show that the neutral propellant starts at a bulk velocity of ~100 m/s at the anode and accelerates to 300-400 m/s by the exit plane. Temperature of the neutrals starts out high (1000-1600 K) near the anode but cools down to 500-800 K near the exit plane. Rapid changes in the strength of the collected fluorescence during the axial sweeps allowed the identification of the approximate ionization zone locations. The anode mass flow rate appears to have a bigger influence on the bulk velocity and temperature of the neutrals than the discharge voltage. Radial sweeps revealed the possible presence of near-wall boundary layers approximately a few mm thick. Implications of these results for Hall thruster physics are discussed.