Fabrication Trials of Round Strands Composed of Coated Conductor Tapes

Various techniques have been proposed in order to assemble coated conductor tapes into high current strands. In this work, the preparation of high current capacity round strands starting from industrial coated conductors has been investigated. Round, twisted strands (about 50 cm long) consisting of stacked tapes sandwiched between two semicircular copper profiles have been assembled following two manufacturing routes: in one case the stack was first soldered to the copper profiles and then twisted; in the second method a twisted strand (stacked tapes between copper profiles) was soldered. The round conductors carry over 400 A at 77 K in self field. Three types of solder alloy were tested: BiSn, InSn, and PbSn. The critical current variation under bending strain was also measured: critical current retention of 99% was observed up to 0.3 % peak bending strain. At 0.6 % bending strain the strands prepared with PbSn solder exhibit a reversible reduction of the critical current of less than 2%, irrespective of the manufacturing route. Such round strands could be used to manufacture flat cables with conventional cabling methods.