Microwave Interferometry (90 GHz) for Hall Thruster Plume Density Characterization

摘要

A phase-bridge microwave interferometer operating at a frequency of 90 GHz (3mm wavelength) is currently under development at the Air Force Research Laboratory (AFRL) at Edwards AFB, California. The motivation for developing this diagnostic is the capability to take time resolved plasma density measurements with higher spatial resolution than other interferometers typically operating at 30 GHz. This interferometer has demonstrated preliminary electron density measurements in the plume of a 200 W Hall thruster. The interferometer has been modified to overcome initial difficulties encountered during the preliminary testing. The modifications include the ability to perform remote and automated calibrations as well as an aluminum enclosure to shield the interferometer from the Hall thruster plume. With these modifications, it will be possible to make unambiguous electron density measurements of the thruster plume as well as to rapidly and automatically calibrate the interferometer to eliminate the effects of signal drift. Due to the versatility of the diagnostic, it is also anticipated that it will be applied to Hall thrusters and large scale pulsed plasma sources under development.