PURPOSE:To enable employment of the title device in the atmosphere of high temperature by using an MI cable, a silica-insulated coaxial cable or a Teflon- insulated coaxial cable as a cable for impression of high voltage and takeout of signals. CONSTITUTION:A connecting outer tube 11, an MI cable 12 of high heat resistance and insulative ceramic 13 insulating a conductor 14 of the MI cable 12 from a sheath are provided. The conductor 14 of the MI cable is connected electrically to a tungsten conductor 8 through a second insulated terminal 6 of a counter tube 9. By using the MI cable 12 as a cable for impression of high voltage and takeout of signals, a prescribed softening temperature is obtained, and therefore employment of the tube in the atmosphere of high temperature is enabled.
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