Present status and strategy of reel-to-reel TFA-MOD process for coated conductors

Abstract On the research and development of a reel-to-reel TFA-MOD (Metal Organic Deposition using Trifluoro-acetates) process, a present status is reviewed and its future strategy is addressed. As a base of the study, the 90 m long tape with uniform I c distribution of the 300 A/cm-width level was obtained on the CeO 2 buffered IBAD-Gd 2 Zr 2 O 7 /Hastelloy C276 substrate. The tape has the 56 m region with the end-to-end I c value of 250 A, which corresponds to maximum product of I c  ×  L of 14,000 Am. Based on the results, several directions on R&D have been studied such as “higher I c ”, “higher I c – B ”, “higher production rate both in coating/calcinations and crystallization steps” and lower cost buffer/substrate”. Then, an extremely high I c value of 735 A/cm-width was achieved in a short tape by the compositional control (e.g. Ba-deficient), in the starting solutions. On the efforts for achieving higher I c – B properties, high I c values of 115 and 35 A/cm-width under the magnetic fields of 1 and 3 T were obtained by the RE mixture of Y and Gd in REBCO, addition of Zr and a growth rate control process. On the other hand, the production rate for the coating/calcinations process was improved by development of new starting solutions, which uses F-free Y salt instead of TFA salt of Y. The high J c value of 1.9 MA/cm 2 was confirmed using the precursor films fabricated at a high traveling rate of 10 m/h. Concerning a higher rate in the crystallization step, the multi-turning system with a vertical gas flow system was developed. The validity of the concept was confirmed using 2-turn parts of the furnace. The high I c value of 250 A/cm-width was realized in the 5 m tape crystallized with a traveling rate of 3 m/h, which is equivalent to 15 m/h for usage of entire area of the furnace of 10-turns. Furthermore, in order to achieve the lower cost, the architecture of the coated conductor with a low cost buffer/substrate system has been developed. An IBAD buffered substrate using IBAD-MgO layer (CeO 2 /LMO/IBAD-MgO/Hastelloy C276) was developed and a high production rate of 24 m/h was realized for IBAD-MgO layer using a small ion gun system with the area of 6 × 22 cm 2 . The grain texturing of the substrate was reached the Δ ϕ value of 4° in the CeO 2 layer. This substrate was applied to the above mentioned multi-turning crystallization furnace for TFA-MOD process. Then, a 5 m long tape with 260 A/cm-width (@77 K. s.f.) was achieved. According to the TFA-MOD process in the above achievements, the prospects of each issue for the future stage were independently confirmed. Consequently, R&D combining the above-mentioned achievements for longer tapes are expected in the next stage.