Current Capacity of Cu-Sheathed Multifilamentary Coated Conductors under the Influence of Spatial Variation of Local Critical Currents in Each Filament

We investigated the relationship between current capacity and local critical current distribution of a Cu-sheathed multifilamentary RE-123 coated conductor (CC). Patterning multifilamentary structure on CC will be a promising solution for reducing magnetization to assure spatial homogeneity and its temporal stability of magnet applications such as MRI and NMR. On the other hand, it will become more difficult to maintain the current capacity because a smaller defect can block the current flow in a narrower filament. Permitting electrical coupling among the filaments will work for maintaining current capacity because current can avoid such a defect by flowing into the adjacent filament. However, too small interfilamentary resistance will result in long time constant of filament coupling, which will affect spatial homogeneity and its temporal stability of magnet applications. Therefore, to design a multifilamentary CC satisfying the requirement from magnet applications, it is necessary to understand the quantitative impact of interfilamentary resistance of the multifilamentary CC on its current capacity under the influence of spatial variation of local critical currents. In this study, we estimated global critical current of a Cu-sheathed multifilamentary CC as a function of interfilamentary resistance by considering its local critical current distribution in each filament. As a result, it was confirmed that the electrical coupling among the filaments was very effective to improve the current capacity of such a multifilamentary CC especially for a section with spatially inhomogeneous local critical currents. Furthermore, it was also found that local heat generation could be significantly suppressed even for a section with relatively homogeneous local critical currents.