CATHODE FOR DISCHARGE TUBE

摘要

PROBLEM TO BE SOLVED: To lengthen the service life of a discharge tube by preventing clouding of a light projecting part of the discharge tube by restraining evaporation of alkaline metal being an electron emitting material at high output operation time by constituting a cathode by pressurizing/sintering it by mixing high melting point powder being the electron emitting material by wt.% of a specific range with high melting point metallic powder. SOLUTION: A cathode support part 3 composed of high melting point metal such as molybdenum and tungsten is fixed by sintering/forming it after pressurization/molding by being uniformly mixed in a 5 to 50 wt.% range at a mixing rate of tungsten boride 1 to high melting point metal. Therefore, the cathode service life can be lengthened by restraining evaporation because of lowness of vapor pressure of the tungsten boricle 1 being an electron emitting material, and reduction in the cathode service life by the fluctuation of an arc can also be prevented without strengthening ion bombardment to a cathode tip part to a degree of melting/recrystallizing the tip by local heating because the tungsten boride 1 existing in the cathode tip part has a comparatively low work function in high melting point metal.