Development of twisted Bi-2212 and Bi-2223 powder in tube conductors for AC applications

Within Alcatel Alsthom Group, Alcatel Cable and Alcatel Alsthom Recherche Center have undertaken a HTc research program, with support from EDF: the aim was to develop conductors suitable for AC applications, where major market opportunities are expected. For AC applications at 50 Hz low AC loss conductors with a resistive matrix material and a twist length of the superconducting filaments of less than 10 mm are required. Bi-2223 and Bi-2212 conductors are fabricated up to lengths of 200 m of 64 filaments tape by the patented rectangular Alcatel Alsthom route. Recently Bi-2212 conductors for 20 K applications have been tested at liquid helium temperatures. Different Bi-2212 conductors with a twist length of 7 to 9 mm, with a silver-alloy matrix and a cross section of 0.5 mm/spl times/3 mm have been realised. In such conductors transport currents of 400-500 A have been measured at 4 K in self fields with a very good reproducibility. The engineering current density in the wire has reached the threshold value of J/sub C/=30'000 A/cm/sup 2/. The superconducting volume fraction of the conductor is 18% which results in a critical current density in the superconductor of J/sub C/=170'000 A/cm/sup 2/. At liquid nitrogen temperature transport currents of 18 A are carried in this conductor. For this temperature range the development of a Bi-2223 conductor is under progress. For instance, different untwisted conductors with transport currents up to I/sub C/(77 K)=60 A and critical current densities up to are realised.