INDIRECTLY HEATED CATHODE HAVING PORTIONS WITH DIFFERENT THERMAL RELATIONS WITH A HEATER

摘要

A cathode for a magnetron comprises a cathode support 1 surrounding a heater 2 and carrying a first electron emitting body 5 and at least one second electron emitting body 12 of a different material which is in poor thermal contact with the support. The first body 5 consists mainly of tungsten and is preferably a dispenser cathode, and the second body 12 consists mainly of molybdenum and is heated by electron back-bombardment, and an annular gap is provided between the support 1 and the second body 12 which is secured to the support by a ring 13. Since the second bodies 12 are thermally insulated from the support they are cooled mainly by radiation, thereby increasing the permissible power of the magnetron. Preferably there are two bodies 12 each of a larger diameter than the first body 5 so that they shield the ends 10 and 11 of the screening hoods 7 and 8 from deposition of emissive material evaporated from the first body 5. The support 1 may be of reduced wall thickness as shown at 15 in the vicinity of the lower second body 12.