Abstract Body

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. The large dynamic resistivity of coated conductors is a major obstacle to improving flux pump performance, and reduction methods are being investigated [1]. 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) [2]. Namely, a dramatic improvement in performance can be expected by using SCSC cables to flux pump systems.

We have been measuring the dynamic resistivity of a spirally wound single copper-plated multifilament coated conductor, i.e., a SCSC cable with a very simple geometry. The results show that the dynamic resistivities could be reduced in SCSC cables as we expected. However, since the distributions of dynamic losses and current distributions in copper-plated multifilament coated conductors or SCSC cables cannot be known from experimental results, we perform numerical electromagnetic field analyses to visualize the electromagnetic field distributions. We analyze four different copper-plated coated conductors; straight monofilament coated conductor, straight multifilament coated conductor, spiral monofilament coated conductor, and spiral multifilament coated conductor. The electromagnetic field distributions in these coated conductors are compared, and also calculated dynamic resistivity will be compared with measurement results.

References

[1] Z. Jiang, K. Hamilton, N. Amemiya, R. A. Badcock, and C. W. Bumby, “Dynamic resistance of a high-Tc superconducting flux pump,” Appl. Phys. Lett., 105, 112601 (2014).
[2] N. Amemiya, M. Shigemasa, A. Takahashi, N. Wang, Y. Sogabe, S. Yamano, and H. Sakamoto, “Effective reduction of magnetisation losses in copper-plated multifilament coated conductors using spiral geometry,” Supercond. Sci. Technol., 35, 025003 (2022).

Acknowledgment

This work was supported by JSPS KAKENHI Grant Number JP20H00245.