Plasma Species Measurements in the Plume of an Iodine Fueled Hall Thruster

The plasma plume from a low-power Hall-effect thruster fueled by iodine vapor was characterized with several wetted plasma probes. The plasma source included a laboratory propellant feed system and a laboratory model Hall thruster powered by a breadboard power processing unit. The hollow cathode was fed with xenon. Iodine and xenon ion velocity and energy distributions were measured with an ExB probe, an electrostatic analyzer, and a combined electrostatic analyzer/ExB probe. Multiply charged species were detected in the plume when the thruster was operated with iodine and xenon. Diatomic iodine ions were also detected. The dimer fraction was found to vary with thruster operating conditions and probe location in degrees from the center of the beam. The dimer fraction was also found to decrease as discharge current and voltage increased. With the thruster operating at a discharge potential of 250 V, the fraction of the high-energy ion flux comprised of dimers exceeded 10% over a broad region of the plume at low power. Significant dimer fractions could increase thrust to power by useful amounts at the cost of some overall efficiency.