Model scandate cathodes investigated by thermionic-emission microscopy

摘要

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, Sc_2O_3, and pulsed-laser-deposited Sc_2O_3 on W substrates have been examined. BaO deposited on Sc_2O_3 is the most stable cathode combination. Measurement of the W-Sc_2O_3-BaO cathode shows that the electron yield enhancement produced by BaO and Sc_2O_3 is a two-step process which requires that the BaO be on top of the Sc_2O_3. BaO does not need to be in direct contact with the W substrate.