Electromechanical Investigation of Different Type YBCO Tapes for Twisted Stacked-Tape Cabling

High-temperature superconductors (HTS), especially YBCO coated tapes, have excellent high current capabilities at high magnetic fields. It is desired to develop a large multistrand cabling method for flat HTS tapes. A cabling method of a twisted stacked-tape conductor for YBCO tapes has been developed recently. A series of tests to electromechanically characterize twisted stacked-tape cabling behaviors using two commercially available types of YBCO tapes was performed. A probe has been developed to simultaneously measure the torsion torque and the critical current as a function of twist pitch for single tapes. The torsion torques and the zero torque twist pitches of YBCO tapes from both manufacturers were determined as a function of twist pitch. The critical currents of those YBCO tapes were also measured in a wider range of twist pitches down to 50 mm. A 25-tape cable of AMSC YBCO was fabricated using the twisted stacked-tape method, and tested at 77 K in self-field. The torque measurements performed on single tapes provide useful information for this cabling process and were taken in consideration in the cable fabrication. The experimental results under torsion for the YBCO tapes from the two manufacturers showed different mechanical behaviors but similar electrical behaviors. Both tapes showed a rapid degradation of critical current for twist pitches below 70 mm. The fabrication of a twisted stacked-tape cable with AMSC tapes was harder than previous fabrication of cables with SuperPower tapes.