A discharge tube in which a cathode with a cathode tip portion being fixed to a lead rod and an anode opposed to the cathode tip portion are encapsulated in a discharge gas atmosphere to effect arc discharge, wherein the cathode tip portion comprises: a metal substrate of an impregnated type in which...http://www.google.se/patents/US6580218?utm_source=gb-gplus-sharePatent US6580218 - Discharge tube
