Influence of laser striations on the properties of coated conductors

Abstract

Due to their high current carrying capability, coated conductors are regarded as the most promising high-temperature superconductor tapes for power applications. However, their high aspect ratio causes too high magnetization losses. To reduce the ac loss, one way is to striate the wide tapes into filaments. We used a picosecond laser for the structuring of (RE)BCO coated conductors. The laser allows to burn 18 μm to 21 μm wide grooves (Ag-cap) with a depth between 0.5 μm to more than 100 μm into the coated conductors, with negligible heat effects at the edges of the structures. Different numbers of filament were structured in Cu-and Ag-cap coated conductors. Patterns with up to 120 parallel filaments in 12 mm wide conductor were made. The critical current and the total ac-magnetization loss were measured as a function of the filament count. With an increasing number of filaments Ic degradation occurs. This current reduction has two contributions, the removed HTS material and current inhomogeneities within the superconductor for instance defects along the tape causing secondary phases. For 120 filaments Ag-cap tapes the hysteresis loss reduction is about two orders of magnitude, as expected. The observation of some remaining filament coupling was investigated.