Unexpected transverse velocity component of Xe+ ions near the exit plane of a Hall thruster
Résumé
The velocity component of singly charged xenon ions in a plane perpendicular to the thrust axis of the 1 kW-class PPS100-ML Hall effect thruster is deduced from laser induced fluorescence measurements on the 5d 2F7/2-->6p 2D5/20 electronic transition at 834.72 nm. Measurements are carried out at several locations in the near field of the channel exhaust. Thruster operating parameters, such as magnetic field strength, discharge voltage, and xenon mass flow rate, are varied over a wide range. The initial aim of this work was to measure the azimuthal velocity of the ions due to their weak magnetic deflection. Surprisingly, experimental results cannot be explained by the one and only Lorentz force acting on Xe+ ions. A realistic picture of the ion trajectory in the E×B drift plane is obtained when adding a velocity component directed toward the external cathode.