Development of scribing process of coated conductors for reduction of AC losses K. Suzuki a,d, * , M. Yoshizumi a , T. Izumi a , Y. Shiohara a , M. Iwakuma b , A. Ibi c , S. Miyata c , Y. Yamada c a Superconductivity Research Laboratory, ISTEC, 1-10-13, Shinonome, Koto-Ku, Tokyo 135-0062, Japan b Research Institute of Superconductor Science and Systems, Kyushu University, 6-10-1, Hakozaki, Higashi-Ku, Fukuoka, 812-8581, Japan c Superconductivity Research Laboratory, ISTEC, Nagoya Coated Conductor Center, 2-4-1, Mutsuno, Atsuta-Ku, Nagoya 456-8587, Japan d Railway Technical Research Institute, 2-8-38, Hikari-Cho, Kokubunji-Shi, Tokyo 185-8540, Japan article info Article history: Available online 25 May 2008 PACS: 81.20.Wk 74.25.Ha 74.25.Sv 74.25.Àq 74.72.Bk Keywords: AC loss Scribing Multifilament Anneal Coated conductor abstract Coated conductors (CCs) are prospective for electric power applications intended for not only better cost performance but also high critical current density (J c ) under magnetic fields comparing with Bi 2 Sr 2 Ca 2 - Cu 3 O y (BSCCO) tapes. Furthermore, they also have a possibility to reduce AC losses by various methods of post-treatments since the CCs are of a laminated structure with the insulating buffer layers. Multifil- amentation by narrowing the tape width is quite effective to reduce the AC losses and therefore this approach is valid for the standard process to fabricate practical CCs with an appropriate architecture. In this study, we developed a tape scribing technique applying a technique of YAG laser with/without chemical etching to control the filament width in YBa 2 Cu 3 O y (YBCO) CCs for the multifilament. The AC loss was reducible to one-twentieth by 20-multifilament structure in a short sample test, and to one- third by 3-multifilament structure in the coil using 28 m long tapes in total. The authors measured the resistance between the filaments at 60–300 K after post-treatment to investi- gate the effective bridged materials, which is essential for decoupling of the filaments. We improved the resistance value between the filaments at liquid nitrogen temperature up to the order of 10 X/cm using the YAG laser with high-temperature oxygen anneals. Furthermore, the resistance over 10 6 X/cm was evident by the combination of laser scribing and chemical etching, which is much higher than the requirements of all the applications. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Coated conductors (CCs) are promising new high-temperature superconductor (HTS) tapes applicable in the near future. They have some advantages such as high J c -B property, high mechanical strength, low production cost, etc., compared with BSCCO wires [1]. Simplicity to form multifilament structure is another potential advantage. It is important to produce multifilament structure to reduce the AC loss. Various researches have investigated in their attempts to in- crease the number of filaments in short samples as referred in [2–6], however the total critical current (I c ) values of the multifil- ament CCs is far behind from the practical requirement. In addition, it is also vital to obtain high electric resistances be- tween the filaments where longer tapes used for the AC applica- tions. Some authors suggested oxygen annealing at 550 °C [6] or 700 °C [7,8] is effective to increase the resistance values due to oxidizing dross between the filaments. However, these electric resistance values (the order of 10 À3 –10 1 X/cm) are low enough for to reduce the AC loss in the case of transformer applications. The required value of electric resistance value would be higher than 10 3 X/cm if their coils were wound by a certain winding method [9]. Most of the researchers have reported the results on the AC loss by their investigations using short samples. Although high electric resistance easily obtainable in the short samples, it is difficult when longer tapes are used. In addition, these have never been the repute on the reduction of the AC loss in coil shape, even if the coil was wound by the multifilament tapes. In this study, we have developed two scribing processes using YBCO tapes. One is a scribing process by a YAG laser to produce multifilament structures in short samples, and another is a combi- nation of the scribing process by a YAG laser with the chemical etching technique to increase the electric resistance between the filaments to reduce the AC loss in coil using longer tapes. Then, we produced two different kinds of coils wound using non-scribed tapes and scribed tapes. We measured the AC losses in these coils by the electrical method. 0921-4534/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2008.05.076 * Corresponding author. Address: Railway Technical Research Institute, 2-8-38, Hikari-Cho, Kokubunji-Shi, Tokyo 185-8540, Japan. Tel.: +81 42 573 7297; fax: +81 42 573 7360. E-mail address: kensuzu@rtri.or.jp (K. Suzuki). Physica C 468 (2008) 1579–1582 Contents lists available at ScienceDirect Physica C journal homepage: www.elsevier.com/locate/physc