Critical current retention in axially strained reinforced first-generation high-temperature superconducting Bi2223 wire

The effect of attaching reinforcing materials to first-generation high-temperature superconducting (HTS) wires on retained critical current (I-c) in axial strain conditions was established by axial tensile and compressive strain loading and in situ I-c tests. Tape-shaped BSCCO/Ag composite wires with copper and nickel plated reinforcing layers of different thickness and tapes with solder-laminated stainless steel, invar and molybdenum with different widths, thicknesses and pre-stresses were made and tested. The > 95% retained I, strain window was found to be shifted in a predictable manner based upon the choice of pre-stress, coefficient of thermal expansion (CTE), geometry and assembly method. Higher CTE and pre-stress in the reinforcement shifted the strain window into the tensile side. All reinforcing materials increased the size of the strain window, with higher modulus materials linearly increasing the strain window by up to two-fold compared to the unreinforced BSCCO-Ag composite. A model was developed to calculate the strain window location and size from reinforcement material properties, pre-stress and process variables. The ability to increase the strain window size and to tailor its location enhances the utility of both first- and second-generation HTS wires.