Oxide cathodes for low-noise travelling-wave tubes

The achievement of low noise in travelling-wave tubes is frequently a measure of the quality of the cathode, and the latter is found to be affected to a major extent by the preparation of the cathode itself and of the manner in which the whole tube is processed. Descriptions are given of various cathode coating techniques and of the alumino-silicate glass envelope system which permits high-temperature baking, enhanced emission and lower noise factors. Results for specific tubes are given.