Electromechanical characterization of superconducting wires and tapes at 77 K

The strain dependency of the critical current in state-of-the-art cuprate high-temperature superconductors (HTS) has been characterized. A universal test machine (UTM) combined with a critical current measurement system has been used to characterize the mechanical and the superconducting properties of conductors immersed in an open liquid nitrogen dewar. A set-up has been developed in order to perform simultaneous measurements of the superconductor lattice parameter changes, critical current, as well as the stress and strain at 77 K in self-field in a high energy synchrotron beamline. The HTS tapes and wires studied were based on YBCO, Bi-2223 and Bi-2212. The YBCO tapes were produced by SuperPower and American Superconductors (AMSC). Two types of Bi-2223 tapes, HT and G, were produced by Sumitomo Electric Industries (SEI). The Bi-2212 wires were produced by Oxford Superconducting Technology (OST) using Nexans granulate precursor, before undergoing a specialized over pressure (OP) processing and heat treatment to optimize Ic at 77. The mechanical properties were determined from engineering stress-strain curves, and critical current was measured at 77 K in self-field. The irreversible strain limit, defined as a 5% permanent reduction in critical current, was observed in the YBCO tapes at 1.05% by AMSC, and 0.72% by SuperPower. For the Bi-2223 samples, the irreversible strain limit was determined to be at the fracture strain, 0.4% for Type HT and 0.2% for Type G. The Bi-2212 wire showed an irreversible strain limit 0.6% strain. The combined lattice parameter, critical current, stress and strain measurements of the Bi-2212 wire and Bi-2223 tape in the high energy synchrotron beamline show that the superconducting portion deforms elastically until the irreversible strain limit is reached.