Thermographic investigation of 3.2 mm diameter orificed hollow cathodes
In an effort to support the needs of emerging low-power electric propulsion systems, efficient, low-current hollow cathodes are being developed at the NASA Lewis Research Center. A thermal model of the hollow cathode is currently under development, and a laboratory model cathode assembly with a removable enclosed keeper was constructed to measure cathode temperature distributions for code validation. The discharge voltage of the cathode was characterized both with the enclosed keeper and in an open geometry with a disk anode. The enclosed keeper configuration exhibited lower voltage operation with higher cathode temperatures over the entire range of operating conditions. In conjunction with the performance evaluations, an imaging radiometer connected to an image acquisition software package was used to measure the cathode temperature distributions along the tube. Thermocouples placed on the cathode were used to calibrate the radiometer. The temperature distributions exhibited complex profiles which indicated either non-uniform emittances or unexpected heat sources. Cathode tube temperature distributions were weakly proportional to flow rate. The temperature distributions along the enclosed keeper also exhibited complex structure. The keeper temperature scaled inversely with the flow rate.
