Near-Plume Laser-Induced Fluorescence Velocity Measurements of a Medium Power Hall Thruster

Abstract

This work presents the near exit plane velocity field of a 600 W Hall thruster at a single operating condition with a 300 V anode potential. The xenon ion propellant velocities were measured using laser-induced fluorescence of the 5d[4] 7/2 - 6p[3] 5/2 excited state xenon ionic transition at 834.72 nm. Ion velocities were interrogated from the acceleration channel exit plane to a distance 100 mm from the exit plane (1.6 exit plane diameters). Both axial and radial velocities were directly measured. A nearly uniform axial velocity profile of approximately 17,000 m/s (197 eV) was measured at the acceleration channel center on the exit plane. The maximum axial velocity was measured 100 mm from the exit plane at 19, 800 m/s (267 eV). In conjunction with the coaxial symmetry of the thruster, radial velocity measurements were used to determine the divergence of the plume, as well as to determine azimuthal velocities in several regions proximate to the exit plane. The 475 m/s mean azimuthal velocity was measured 5 mm from the exit plane. From this value, it was possible to estimate a maximum thruster-induced torque of 3.2 x 10 -5 Nm. Because of the divergence and convergence of the coaxial ion flow, distinct ion populations were observed to interact in the central core of the near plume. This was apparent in measurement volumes where multiple radial and axial velocity components were measured. These regions also typically correspond with the brightest portions of the visible plume.