Patent ID: 6548959
Filing Date: 2003-04-15
Classification: H01J

Abstract:
A discharge tube comprising:a vessel filled with a discharge gas; a cathode placed in said vessel and having a tip portion fixed to a lead rod; and an anode placed opposite to said tip portion of said cathode in said vessel, wherein said cathode comprises; a cusp pointed toward said anode; a metal substrate of an impregnated type in which a porous refractory metal is impregnated with an electron-emissive material or a sintered type in which a refractory metal containing an electron-emissive material is sintered; and a coating of a refractory metal which covers a surface on the base end side of said cusp, and wherein an exposed portion in which said metal substrate is exposed without being covered by said coating is provided at a tip portion of said cusp of said cathode.