Neutral Flow Evolution in a Six-Kilowatt Hall Thruster

Laser-induced fluorescence velocimetry measurements obtained from the interior of a 6-kW Hall thruster using the Xe I 6s 3=2 02 ! 6p 3=2 2 transition at 823.4 nm (vacuum) and the Xe I 6s0 1=2 01 ! 6p0 3=2 2 transition at 834.9 nm (vacuum) are presented. 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. Velocimetry results along the channel centerline show that the neutral propellant leaves the anode at a bulk axial velocity of 100 m=s and accelerates to 300–400 m=s by the exit plane. The temperature of the neutrals starts out at 1000–1600 K near the anode but cools down to 500–800 K near the exit plane. 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 across the channel exit plane revealed the presence of near-wall boundary layers approximately a fewmillimeters thick. The experimental results are compared with MONACO and HPHall-2 simulation results. The comparison suggests that the neutral-flow acceleration is due to a combination of wall thermalization, hydrodynamic, and ionization effects.