Reducing ac losses in coated conductors is the most important issue for HTS application to electric power devices and magnets. Multifilament structure is a method to reduce ac losses. From the view point of improving the robustness of a multifilament coated conductor for local normal transitions, it is preferable to have a finite transverse conductance between the filaments because it facilitates current sharing among the filaments. When copper is plated over the superconductor filaments to allow current sharing, the effect of multifilament structure to reduce ac losses can be obtained only after the decay of coupling currents flowing through the transverse conductance and the superconductor filaments. To make coupling time constant shorter, we proposed spiral copper-plated striated coated-conductor (SCSC) cables.

We have been developing numerical electromagnetic field analysis model for SCSC cables. In the model, copper-plated multifilament coated conductors are modelled as thin-strips composed of superconductor filaments and resistive strips between the filaments as shown in Figure 1. At the beginning, in order to decide conductivity σ_n of the resistive strips, we conducted static electric field simulations for a straight copper-plated multifilament coated conductor. Second, using obtained σ_n, we conducted numerical electromagnetic field analyses for the multifilament coated conductor exposed to external magnetic field. Here, since the periodic structure of the superconductor filaments and the resistive strips in the thin-strip affects convergence of the analysis, preconditioning of matrices in finite element method by Algebraic Multigrid (AMG) method was applied to deal with this problem. Then we compared analysis results and measurement results of coupling losses to validate our model.

Subsequently, we developed large electromagnetic field analysis model for SCSC cables composed of dozen of the multifilament coated conductors. To handle large degree of freedom in the analyses, we use hierarchical matrices. The analyzed SCSC cable was modelled with finite length. In the presentation, we will report analysis results of ac losses and dynamic resistance of a finite long SCSC cable.

This work was supported in part by JST-Mirai Program Grant Number JPMJMI19E1, Japan.

Keywords: Electromagnetic field analysis, Multifilament coated conductor, SCSC cable, AC loss