Characterization of Local Critical Current Distribution in Multifilamentary Coated Conductor Based on Reel-to-Reel Scanning Hall-Probe Microscopy

We have carried out the characterization of local critical current distribution in a 113-m-long multifilamentary coated conductor (CC) based on reel-to-reel scanning Hall-probe microscopy. Patterning multifilamentary structure on CCs is a key technology for the reduction of ac losses due to magnetization. Recently, this advantage has also been expected for the reduction of the magnetization in a coil winding which has been recognized as a critical problem for HTS magnet applications such as accelerators, MRI, and NMR from the viewpoint of field homogeneity and temporal stability. However, it has been difficult for the conventional techniques such as four-probe method, TAPESTAR, etc., to make diagnostics for multifilamentary CCs due to the limitation of spatial resolution. On the other hand, our measurement has an advantage in taking two-dimensional field image. This enabled us to confirm that multifilamentary structure as well as the corresponding magnetization reduction was successfully achieved in a long-length CC. At the same time, by the estimation of local critical current distribution for each filament, it was also found that there were still some local defects, which affected the global performance of the multifilamentary CC, even if the probability density of such defects was only in the order of 10^-5. These findings will become crucial information for the optimization of fabrication processes of multifilamentary CCs and for their nondestructive quality assurance.