Dynamic resistivities are generated in superconductors carrying dc currents under ac magnetic fields. Loss due to the dynamic resistivity (dynamic loss) is a type of hysteresis losses associated with the flux motion in superconductors. In coated conductors, multifilament structure, which divides the superconductor layer into multiple filaments in the width direction, is considered effective in reducing the dynamic loss and dynamic resistivity. However, in practical use, coated conductors are used with plated copper for improvement of stability, so that coupling currents are induced under ac magnetic fields, and the effect of multifilament structure can be obtained only when the time constant of the ac magnetic fields is sufficiently larger than the decay time constant of the coupling currents. To solve this problem, we have proposed a cable consisting of copper-plated multifilament coated conductors spirally wound around a cylindrical core, which we call spiral copper-plated striated coated-conductor (SCSC) cable (Figure 1).
We measured the dynamic resistivities and evaluated them by numerical electromagnetic field analyses to see if the reduction of the dynamic resistivities can be realized in SCSC cables. The dynamic resistivities in straight monofilament and multifilament coated conductors, and spiral monofilament and multifilament coated conductors are measured. We observed voltage evolution in the samples carrying dc transport current under ac magnetic fields and calculated dynamic losses from the measured voltage wave forms. Also, the same samples are numerically analyzed. As the results, the dynamic resistivity in straight copper-plated multifilament coated conductor was not reduced from it in straight monofilament coated conductor. However, it was confirmed that the dynamic resistivity was greatly reduced by making the copper-plated multifilament coated conductor spiral.

This work was supported by JSPS KAKENHI Grant Number JP20H00245.

Keywords: Coated conductor, SCSC cable, Dynamic resistivity, AC loss