Speaker
Description
A Bi2212-based, high temperature superconductor has been developed in reinforced, rectangular wire forms, with up to 400 MPa stress tolerances and useful current densities, making them suitable for application in some coils that are problematic with wide HTS tapes, and that need to operate beyond the field and temperature limits of low temperature superconductors. However, the development of a round wire version has been delayed primarily because of the difficulties in suitably attaching the reinforcement to the curved round wire surfaces. Recently, however we have succeeded in developing, building and qualifying the equipment and tooling for successfully assembling very high modulus, thin reinforcement strips onto nominally 0.8 – 1.2 mm diameter 2212/Ag round wires. With this capability in hand, we are now developing the full process for strong, high Je 2212 round wires, as well as their configurations, including strip dimensions, number of strips, assembly pitches, and with characterization of strip adhesion, wire tensile and bend properties before and after final reaction, and electrical transport properties. As an example, 1.2 mm diameter wire has been produced with addition of 0.1 mm thick reinforcement onto 1 mm diameter 2212/Ag wire, uniformly covering about 80% of its surface and leaving sufficient openings for the required oxygen exchange during final reaction. This wire’s stress tolerance is ~ 400 MPa at the onset of Ic degradation, and its Je in a 5T field at 4.2K is ~ 500 A/mm2 (5T is a current test standard). Bend testing of the diffusion bonded architecture prior to reaction indicates a high degree of formability without damage – to ~ 1 cm diameter, showing great promise for both winding small diameter coils, as well as using the type of cabling approaches that are well developed for producing high current, transposed LTS cables.