Model scandate cathodes investigated by thermionic-emission microscopy

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Abstract
Model thermionic cathodes with different oxide coatings have been surveyed using a combination of photoelectron emission microscopy and thermionic electron emission microscopy. The model cathodes are imaged directly at operating temperatures and the electron yield is measured with a Faraday cup located in the image plane. Cathodes with combinations of Ba, Sc, BaO, Sc2O3, and pulsed-laser-deposited Sc2O3 on W substrates have been examined. BaO deposited on Sc2O3 is the most stable cathode combination. Measurement of the W–Sc2O3–BaO cathode shows that the electron yield enhancement produced by BaO and Sc2O3 is a two-step process which requires that the BaO be on top of the Sc2O3. BaO does not need to be in direct contact with the W substrate.

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