Experimental Study of the Heater Performance of a High Current Hollow Cathode

Thermionic hollow cathodes are electrodes mainly used in Hall-effect and Ion thrusters and they are crucial parts of those electric propulsion devices. Cathodes are subjected to extreme environments during operation and thousands of cycles of high power ignitions. The most sensitive part of the cathode, apart from electron emitter, is a heater that has a high record of failure and meltdown. Designing a more reliable heater is essential for the future development of high current hollow cathodes. HC60 is a high current hollow cathode currently under development at Sitael. In order to verify heating performance of the new heater solution, the real HC60 heater is installed on the real cathode tube and tested. To ensure representativeness in terms of thermal behavior, a mock-up of the additional cathode elements were used to reproduce the thermal capacitance and conductivity that will be experienced by the HC60 during operation. The purpose of this approach was to estimate the heating performance of the cathode and thermal transient behavior during the ignition phase. Additionally, cathode mock-up was cycled up to ignition temperature multiple times to test the thermo-mechanical robustness of the heater assembly. Comsol software has been used to verify if the cathode mock-up design is thermally representative. Heat Transfer analysis is divided into two cases. Case 1 is considering cathode assembly mockup mounted on support flange while Case 2 is analyzing original titanium interface. Results of the first and second case analysis were used for comparison and validation of thermal behavior of the cathode assembly mockup, particularly considering percentages of heat dissipated by means of heat conduction and radiation. Finally, results of two major tests were compared with thermal model and suggestions about design changes and improvement possibilities are presented