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 · m²/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 × 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 × 4 mm 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 × 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/cm² at 77 K were observed in YBCO films. The CC tapes exhibit favorable behavior under axial stress and sufficiently small ac losses.