Low perturbation interrogation of the internal and near-field plasma structure of a Hall thruster using a high-speed probe positioning system.

摘要

This thesis presents research aimed at characterizing the internal and near field plasma structure of a Hall thruster. This information is vital to extending our understanding of the physical processes in the Hall thruster. In turn, this aids in the design of next generation Hall thrusters with improved performance both directly and through the validation of thruster models.; Internal plasma parameter measurements were accomplished using a unique High-speed Axial Reciprocating Probe (HARP) system. The HARP system enabled, for the first time, the insertion and removal of probes from the Hall thruster discharge channel while minimizing perturbation to thruster operation. The system was used with an emissive probe to map plasma potential and with a double Langmuir probe to map electron temperature and ion number density. Thruster perturbation, determined by monitoring discharge current, was less than 10% for the majority of measurements.; Using the data obtained with the HARP, a number of thruster parameters were investigated on a PEPL designed and built Hall thruster, the P5. The magnitude and spatial structure of the Hall current is presented and its contribution to propellant ionization and self magnetic fields discussed. The classical Hall parameter is compared to that inferred from the generalized Ohm's law. Thrust and beam current are computed and compared to direct measurements from a thrust stand and Faraday probe, respectively.; Ion number density profiles are compared with results from a two dimensional numerical model, which predicted similar qualitative profiles. Combining data from the P5, SPT-140 and the model, it was surmised that a radially symmetric magnetic field would provide increased performance by generating a more collimated ion beam.