A hollow cathode produces electrons which neutralize ions from electric propulsion thrusters. After hundreds to thousands of hours of operation in space, the cathode materials can be significantly eroded due to ion bombardment. As a result, the electric propulsion system performance will be obviously changed or even fail. In this work, the erosion products from a LaB hollow cathode (widely used presently in electric propulsion systems) are studied by using a specific detection system, which consists of a molecular beam sampler and a time-of-flight mass spectrometer. This system measures trace-level-concentration (10-10) products. Boron (B), tantalum (Ta), and tungsten (W)-originating from the emitter, keeper, and orifice of the hollow cathode-are measured. It is found that the erosion rate is significantly influenced by the gas flow rate to the cathode.
Monochromatic radiation thermometry is used to quantify temperature distribution during the start-up process for a heaterless hollow cathode. A transparent cathode is designed to facilitate the transmission of thermally and spontaneously radiated photons from the interior of the structure and their reception by the detection equipment. The relative radiation intensities can be obtained by the developed measurement equipment, which consists of an sCMOS camera and a 780 nm narrow-band filter, and then transformed into temperature distributions calibrated by a two-color pyrometer. The current and voltage characteristics of the anode and keeper and plasma image captured by the high-speed camera are used to analyze the thermal evolution mechanism. A 2-D extended fluid model coupling with a thermal model is also developed and used to help clarify the thermal deposition variation at different locations. These results provide further support for the hypothesis that thermal deposition of ions and electrons, thermal conduction, and thermal radiation all affect the rate of change in temperature of various components.
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