Measurement of the azimuthal rotation of plasma in the near plume of a Hall Effect Thruster

Evaluation of torque produced by a Hall Effect Thruster (HET) is a challenging task. Apart from the direct weighing on a torque balance, several studies have been accomplished in the past and recently to measure both radial [1] and azimuthal velocities [2] in the near plum of low and high-power HETs using the Laser-Induced Fluorescence. The latter gives the best-in-class ion velocity resolution on the order of 100m/s, but it is a complex experimental technique. Our high-resolution spectroscopic system presently has ~0.1-0.2 pm/pixel resolution, which corresponds to ~200m/s resolution. We tried measuring azimuthal velocity in the near plume with krypton propellant, but our data were inconsistent [3]. We report on the experimental setup upgrade and results for argon propellant. [1] W.A.Hargus, M.R.Nakles, Evolution of the Ion Velocity Distribution in the Near Field of a 200 W Hall Thruster, AFRL-ERS-PAS-2006-104, 2006; [2] V.H.Chaplin et al, Azimuthal Ion Velocity Measurements in the 12 kW HERMeS Hall Thruster, IEPC-2024-207, 2024; [3] O.Batishchev, A.Hyde, J.Szabo, Spectral characterization of the Hall Effect thruster operating on Kr propellant, 63^rd APS DPP, PP11.00028, 2021