INDIRECTLY HEATED CATHODE STRUCTURE

摘要

PURPOSE: An indirectly heated cathode structure is provided to control the amount of electron beam in an accurate manner by preventing leakage current between the heater and metal base. CONSTITUTION: An indirectly heated cathode structure comprises an electron emitting member(21) for emitting thermal electrons when heated; a metal base(22) having a fixed portion(22a) where the electron emitting member is mounted, and a skirt portion(22b) extended downward from an edge of the fixed portion; a heater(23) mounted inside of the metal base; and an insulation layer(24) having a lower insulation layer(24a) constituted by a P-type semiconductor coated at the outer periphery of the heater, and an upper insulation layer(24b) constituted by an N-type semiconductor coated at the outer periphery of the lower insulation layer. Thus-configured indirectly heated cathode is capable of preventing current leakage between the heater and the cathode even at a high temperature of 1000°C or higher.