R&D for long tapes with high Ic by advanced TFA-MOD process

Recent progress in the research and development of the TFA-MOD processing for the coated conductors was reviewed. For the higher Ic performance, crack generation in the thick films was a problem, which limits increasing Ic values. It was found that both lower heating rate and low PH2O in the crystallization step are effective to improve the critical thickness for obtaining crack-free films. However, the high PH2O is preferable for a high production rate and high Jc performance. Then, the new heat treatment profile, which could suppress crack formation even in thick films under the high PH2O, was developed. Consequently, the high Ic value of 470A at 77K was realized in the film with 3μm in thick. Concerning the long-tape processing, the key factors for high Ic performance by TFA-MOD process were investigated. The highly textured substrate for high crystallinity of the YBCO layer, the thick film with maintaining reasonable high Jc and full conversion reaction to form the YBCO layer are important to obtain high superconducting performance in long tapes. At present, a 25m long tape with a reasonable high Ic value of 100A, and a high Ic value of 250A in a 4m long tape were achieved. In order to realize a high production rate, the processes for both calcination and crystallization steps have to be developed. In the calcination step, the multi-turning continuous system was developed to maintain an effective travelling rate even in the multi-coating method. On the other hand, in the crystallization step, it was confirmed that optimization of the processing parameters such as a high water vapour partial pressure, a low total pressure, and a high gas flow rate could make the YBCO growth rate increase. The combination effect of these parameters is experimentally confirmed and the 5 times higher production rate was achieved in the crystallization step. Additionally, the equipment design of the multi-turning system with a new gas flow concept, which is a vertical gas flow system, was investigated by means of both numerically and experimentally, and the concept was confirmed at least. Consequently, a high production rate over 5m/h could be expected by combining the above mentioned effects.