SCSC-IFB cable: a novel low-AC-loss cable composed of multifilament coated conductors with superconducting inter-filament bridges

Abstract Current sharing between filaments is necessary in multifilament coated conductors to bypass local defects arising from the fabrication process and to impede current transport in each filament. We propose a novel cable concept, termed the spiral copper-plated striated coated conductor with inter-filament bridges cable (SCSC-IFB cable). In this design, copper-plated multifilament (striated) coated conductors incorporating IFBs—non-striated sections between filaments—are helically wound around a central core. In contrast to current sharing through copper plating, i.e. , the current meandering through it to avoid local defects on filaments, which generates a small but finite voltage, current sharing through IFBs produces no voltage and thereby does not affect the electric field–current characteristics of multifilament coated conductors. Similar to twisting in conventional low T c superconductors, helical cabling decouples filaments electromagnetically against a transverse alternating current (AC) magnetic field. We experimentally confirmed that IFBs improve the electric field–current characteristics, i.e. , the n -values, and that the helical cabling does not affect them, by using 2 mm-wide copper-plated 10-filament coated conductors with IFBs. Using the same coated conductors, we wound short pieces of the monolayer SCSC-IFB cables and examined their AC loss characteristics under a transverse AC magnetic field at 77 K. Importantly, the bridge intervals were designed to exceed half the cabling pitch, preventing superconducting loop currents through two IFBs that could otherwise couple the filaments. The measured coupling time constant was 19 μ s, which is sufficiently small for a wide range of applications. Furthermore, the magnitudes of the measured magnetisation losses above the penetration field of each filament are nearly identical to the theoretical values predicted for cables composed of multifilament coated conductors with electromagnetically decoupled filaments.