Evaluation of a Magnetically-Filtered Faraday Probe for Measuring the Ion Current Density Profile of a Hall Thruster

The ability of a magnetically-filtered Faraday probe (MFFP) to obtain the ion current density profile of a Hall thruster is investigated. The MFFP is designed to eliminate the collection of low energy, charge-exchange (CEX) ions by using a variable magnetic field as an ion filter. In this study, a MFFP, boxed Faraday probe (BFP), and nude Faraday probe are used to measure the ion current density profile of a 5 kW Hall thruster operated over the range of 300-500 V and 5-10 mg/s. The probes are evaluated in the University of Michigan Large Vacuum Test Facility at operating pressures within the range of 3.3x10-6 Torr to 8.4x10-6 Torr on xenon in order to study the ability of the Faraday probe designs to filter out CEX ions. Detailed examination of the results shows that the nude probe measures a greater ion current density profile than both the MFFP and BFP over the range of angular positions investigated for each operating condition. Because all other parameters are identical, the differences between the current density profiles obtained by each probe are attributed to the ion filtering systems employed. Analysis of the results shows that the MFFP provides the best agreement with flight-test data and between operating pressures