Saturday, 3F-09, 9:50-10:10

Striation and Diffusion Joint for Coated Conductor

Keiichi Tanabe

Takato Machi, Naomichi Sakai, Junko Kato, Tsunehiro Hato, and Noriko Chikumoto

Superconductivity Research Laboratory, ISTEC, 1-10-13 Shinonome, Koto-ku, Tokyo 135-0062, Japan
Tel. +81-3-3536-0617, Fax. +81-3-3536-5717, tanabe@istec.or.jp

It is indispensable to decrease AC loss in order to apply coated conductors (CCs) to power equipment such as transformers. It was previously demonstrated that striation into multi-filamentary structures effectively decreases AC loss of a coil wound with totally 70-m-long CCs. For practical transformers, however, much longer and narrower multi-filamentary CCs are required. There seem to be two major problems in fabrication of such multi-filamentary CCs. One is lower inter-filament resistance leading to larger coupling loss, and this would be caused by low resistance of the buffer layer or defects occurring in the striation process. The former cause could be eliminated by optimizing the buffer layer architecture, while the latter could be prevented by improving the striation process. We have recently improved our striation process by a laser-scribing method. By employing shallow laser scribing and two-step chemical etching for Ag and HTS layers, we have successfully reduced the slot width to less than 150 mm keeping high enough inter-filament resistance with high reproducibility. The other major problem is I_c non-uniformity across the width as well as along the length of CCs, which leads to a substantial decrease in the minimum filament I_c. Our strategy is to preselect CCs in terms of I_c uniformity using non-contact characterization techniques such as Hall-sensor-array and recently developed SQUID-array systems. The latter system can be also utilized to find the positions of macroscopic defects in striated CCs where we apply repairs using a diffusion joint technique. We will also discuss the prospects for the diffusion joint technique.

This work was supported by the New Energy and Industrial Technology Development Organization (NEDO).

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