Method of constructing a normal joint structure of a superconducting cable

A method of constructing a normal joint structure for connecting superconducting cables each having a cable core, a tubular member arranged along the cable core, and an optical fiber housed in the tubular member and arranged along the cable core, the tubular member being configured to have a structure such that the optical fiber housed therein can be in contact with a coolant that is filled inside the tubular member, the method including the steps of:

• pulling out an optical fiber from the end of each of two superconducting cables to be connected together and splicing the optical fibers thus pulled out;
• returning the excess length of the pulled-out optical fiber to a superconducting cable side by pulling or pushing-in upon the completion of splicing;
• connecting the cable cores;
• and
• storing the connected cable cores in a joint box formed so as to include a coolant vessel and a vacuum vessel,
• wherein after the joint box is formed, a space located between the coolant vessel and the vacuum vessel is evacuated so that a thermal insulation function is afforded to the vacuum vessel,
• wherein the joint box is equipped with a vacuum layer, and
• wherein a thermal insulation material is arranged between the coolant vessel and the vacuum vessel in addition to the evacuated space.