| 简介 |
PROBLEM TO BE SOLVED : To provide a structure that can prevent excessive evaporation of an emitter from a cathode and thus depletion of the emitter at an early stage and also enables smooth lighting even under initial lighting in a discharge lamp in which an emitter other than thorium is added to a cathode in an arc tube.
SOLUTION : A main body portion 31 of a cathode 3 is formed of a metal material having a high melting point which contains no thorium, and a tip portion 32 is formed of a metal material having a high melting point which contains an emitter (excluding thorium). A tungsten sintered body containing an emitter formed of rare earth oxide having a higher concentration than the emitter concentration contained in the tip portion is embedded in a sintered body mount space 33a in a hermetically sealed space formed in the main body portion and/or the tip portion, and a vapor phase diffusion space 33b in the hermetically sealed space is formed in the tip portion.
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