Fabrication of square and round Ag/Bi(2223) wires and their ac loss behaviour

Abstract

Square and round wires have been fabricated by using a combination of two-axial rolling and drawing in order to reduce the effect of field anisotropy and to confirm the decrease of ac losses predicted by calculation. Critical current measurements, as a function of magnetic field angle, confirmed that the symmetrical configuration of filaments inside the wire leads to an almost angle-insensitive behaviour of Jc(B). The Bi(2223) grains in our wires have a higher misalignment angle (around 8°) with respect to flat tapes, due to the particular wire configuration and the use of two-axial rolling. Therefore, the Jc values in our square wire are somewhat lower, 11 kA cm−2 at 77 K and zero field. AC loss measurements showed that the combination of wire geometry and twisting leads to strongly reduced ac losses in square Ag/Bi(2223) wires when compared to flat tapes: the value of 0.53 mW A−1 m−1 was measured, regardless of the field direction.