SUPERCONDUCTING COIL

PROBLEM TO BE SOLVED: To provide the connecting structure of a forced cooled conductor having high mechanical strength and low connecting electric resistance, generating little Joule's heat at a connection section, and excellent in superconductivity stability. SOLUTION: Superconducting stranded wires 3 at a connection end are covered with a copper pipe 2 of an electric connecting member, a current flows from the superconducting stranded wires 3 to other electric members via the copper pipe 2, and refrigerant helium circulates in gaps between the superconducting stranded wires 3 in the copper pipe 2 during operation in the connecting structure of a cable-in-conduit type forced cooled conductor constituted of Nb3Al or Nb3Sn compound superconducting strands. A metal foil of copper or silver having the thickness of 1/50 of that of the copper pipe 2 and low electric resistance is arranged at the contact boundary face section between the superconducting stranded wires 3 and the inner wall of the copper pipe 2. The porosity at the connection end section where the refrigerant helium circulates in the copper pipe 2 is set smaller by 10-15% than the porosity at portions other than the connection end.