Processing of Long-Length YBCO Coated Conductors Based on Stainless Steel Tapes

Recent progress is reported in the development of long lengths (up to 100 m) of YBCO coated conductors with good mechanical stability and improved critical current homogeneity. A non-magnetic CrNi stainless steel tape, 0.1 mm thick, is employed as a substrate tape. Prior to deposition, the tape is coated with yttria stabilized zirconia in the form of a bi-axially textured buffer layer, using a novel "alternating beam assisted deposition" technique. After deposition of a ceria cap layer onto the buffer, YBCO films are deposited employing a high-rate pulsed laser deposition method that allows higher critical current densities and incurs a lower YBCO loss (~10%) than other deposition techniques. The last processing step consists of coating the with a thin layer of silver or gold and a 2-40 mum thick copper shunt layer. In 40 m long tapes with a 1 mum thick YBCO film (at 77 K and zero external field), critical current, J_c, up to 235 A per cm-width were obtained. Higher critical currents, up to 574 A per cm, were achieved in short 0.2-7 m sections corresponding to current densities, J_c, of up to 4.4 MA/cm² . The critical current homogeneity and performance of our improved coated conductors under applied temperature cycling, multiple quench-recovery cycles, and repeated bending are reported.