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Feasibility studies on applying high-temperature superconductors (HTS) to the LHD-type heliotron fusion energy reactor FFHR are being carried out. Because the HTS conductor has high cryogenic stability at elevated temperature operations (e.g. 20 K) and the refrigeration power has enough margins, it is considered that Joule heating dissipation generated at joints of conductors is acceptable to facilitate the segmented fabrication of the helical coils of FFHR. In this study, the joint resistance with 10-kA class YBCO conductors has been measured to evaluate the joule heating dissipation in the FFHR magnet. The experiment has been carried out by fabricating a soldered lap joint and a mechanical lap joint. The feasibility of segmented fabrication is examined by the measured results.

To evaluate butt joint fabrication technology of Nb 3 Sn cable-in-conduit (CIC) conductors, joint resistance and quench current were measured using a joint sample developed for the JT-60SA central solenoid (CS) coil. The measurements indicate that the butt joint fulfilled the design requirements. To simulate the butt joint characteristics, a one-dimensional numerical model simplifying the butt joint configuration was developed. Using the model, joint resistance and quench current of the butt joint were calculated. The calculations were in good agreement with the measurements. As a result, the model is valid for butt joint simulations.

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