JPH0459763B

PURPOSE:To enlarge a cooling surface area, to which helium gas is contacted, and to improve cooling efficiency, the forming a round rod by winding good electric conductor such as copper and copper alloy around the outer surface with a stainless steel rod as a core, and inserting a plurality of the round rod conductors tightly in the inside of a hollow tube. CONSTITUTION:The outer surface of a stainless steel rod, which has a sufficient strength at a very low temperature is wound with a good electric conductor 22 of copper, copper alloy and the like, and a round rod conductor 20 is formed. A plurality of the round rod conductors 20 are tightly inserted in the inside of a hollow tube 8. The outer surface of the hollow tube 8 is wound with an insulator 11. A gap in the hollow tube 8 is made to be the path of helium gas. The stainless steel rod can be replaced by other materials such as a manganese steel rod and a nichrome steel rod, which have small heat conductivity and a high strength.