Large area YBCO-coated stainless steel tapes with high critical currents

Recent progress in developing large area HTS-coated stainless steel tapes is reported. YBCO films have been grown on IBAD-YSZ buffered 0.1 mm-thick steel tapes using a High-Rate Pulsed-Laser-Deposition technique which allows a deposition rate up to 70 nm . m(2)/h. The coated conductors (CC) are provided with an optimized shunt layer and current contacts which reduce the generation of Joule's heat. An advanced technique for critical current I-c measurements was developed. The effects of self-field and time relaxation of current in helically wound tapes are analyzed. In long tapes of 10 m x 4 mm, the highest I-c of 78 A at 77 K was observed. Critical currents of 67-75 A were reproducibly achieved in (8-10) m x 4 rum coated tapes. For shorter tapes with a length of 0.2-1 m, critical currents of 317-391 A/cm width of the tape were observed. Fifteen wider CC tapes of 0.6 m x 43 mm with I-c = 700 A have been manufactured and employed in newly developed fault current limiters with a nominal current of 3 kA. Critical current densities J(c) = (1.3 - 2.5) MA/cm(2) at 77 K were observed in YBCO films. The CC tapes exhibit favorable behavior under axial stress and sufficiently small ac losses.