Development of TFA-MOD Process for Coated Conductors in Japan

Progresses in the development of the TFA-MOD process for the coated conductors in Japan are reviewed. In the fundamental approaches, some important advantages of Ba-poor starting solution were found such as for obtaining higher
Jc
, shorter reaction time and wider process temperature window. The high
Ic
value of 735 A/cm-w@77 K was attained. Additionally, introduction of artificial pinning centers by Sm-substitution and Zr-addition to the Ba-poor films was successfully investigated. The films showed a high minimum
Ic
value of 42 A/cm-w at 77 K, 1 T. Furthermore, isotropic
Ic
properties in the angular dependence of applied magnetic fields was realized by the uniform distribution of nanoprticles of Zr-compound. On the other hand, two different process of MOD including batch and reel-to-reel (RTR) types have been developed as an engineering process for low cost and long tape production with high superconducting performances at a high rate. In the batch type, long tape synthesis process could be developed by the optimization of the growth conditions in a large furnace. A 500 m long tape was heat-treated and a high Ic value of 310 A/cm-w in a 250 m tape was confirmed. Concerning the RTR type, a high production rate system was developed after confirmation of the ability of the continuous process in a 90 m long tape. A multi-turn with a vertical gas flow system was developed for this purpose. This system was applied to the fabrication of superconducting films on the lower cost buffer layers including a high deposition rate IBAD-MgO layer. Currently, a 5 m long tape with 250 A/cm-w was obtained at the production rate of 3 m/h using a part of the multi-turn system, which is equivalent to 15 m/h in the entire use of the furnace.