AC Loss and Coupling Currents in YBCO Coated Conductors With Varying Number of Filaments

Striation of high-temperature superconductor coated conductors as a way to reduce their magnetization ac losses has been the subject of intense worldwide research in the past years by several groups. While the principle of this approach is well understood, its practical application on commercial materials to be used in power applications is still far to be implemented due to manufacturing and technological constraints. Recent advances in tape quality and striation technology are now enabling systematic investigations of the influence of the number of filaments on ac loss reduction with a consistency that was not available in the past. In the present work, we demonstrate the technological feasibility of importantly reducing the magnetization losses of commercially available coated conductors by striating them into a high number of filaments (up to 120). The loss reduction exceeds one order of magnitude and does not come at the expense of current-carrying capability: samples with 10 and 20 filaments are unaffected by the striation process, whereas samples with 80 and 120 filaments still retain 80% and 70% of the current-carrying potential, respectively. We also investigate the transverse resistivity between the filaments in order to understand the paths followed by the coupling currents: we found that the coupling current prevalently flows in the metallic substrate, rather than in and out of the filaments. Finally, we use oxidation as a method to reduce the coupling currents and the corresponding losses. The contribution of this work is threefold: 1) it describes the know-how to produce a large number of high-quality striations in commercially available coated conductors, greatly reducing their losses without extensively degrading their transport properties; 2) it provides a comprehensive characterization of the said samples (e.g., measurements in a wide frequency range, transverse resistance profiles, influence of oxidation on dc and ac behavior of the sample); and 3) it provides new insight on the patterns of the coupling currents.