Gaseous electric discharge tube having a coaxial, hollow cathode structure

In a discharge tube having an anode and a cathode the improvement which comprises a generally cylindrical cathode having disposed thereabout in coaxial relationship a generally cylindrical auxiliary anode, said auxiliary anode having a diameter greater than said cathode and disposed with a first axial end portion overlapping a first axial end portion of said cathode, said auxiliary anode having an axial portion extending closer to the anode than said cathode to provide shielding for said cathode, said discharge tube being provided with an argon filling at a pressure between 0.05 and 5 Torr at a cathode current in the order of tenths of amperes, said cathode being non-activated and comprising inner and outer tubes of a material selected from the group consisting of tantalum and tungsten, said inner and outer tubes being disposed in coaxial relationship with at least a first axial extremity of said outer tube overlapping a first axial extremity of said inner tube, said inner and outer tubes being open at said first axial extremity which faces the discharge, the first axial extremity of said inner tube ending within the first axial extremity of the outer tube and the outer tube being carried on the circumference of the inner tube, and means for supporting said inner tube carried on said discharge tube.