Reliable fabrication process for long-length multi-filamentary coated conductors by a laser scribing method for reduction of AC loss

Abstract

We have developed a reliable fabrication process based on a laser scribing method for multi-filamentary coated conductors with a low alternating current loss. This process consists of shallow laser irradiation and two-step chemical etching. The shallow laser irradiation, which penetrates into only a masking polymer tape and a silver stabilizing layer, suppresses generation of dross that is formed due to melting and hardening of a metal substrate. The two-step chemical etching individually for the stabilizing and the superconducting layers prevents over-etching of the superconducting layer and thus suppresses degradation of the critical current (Ic). By using the developed laser scribing process, we realized an improvement of processing speed and a reduction of Ic degradation at the same time. Subsequently, we developed reel-to-reel equipment to apply this process to coated conductors several hundred meters long. We succeeded in fabricating 280 m and 70 m long coated conductors with 5 mm width divided into three and five filaments, respectively. It was confirmed that they had one-third and one-fifth hysteresis loss, respectively, in comparison with that before processing, and high inter-filament resistance, over 0.1 MΩ cm. The typical degradation rates of Ic in the developed laser scribing process were less than 20%.