Bi-2223 tapes for applications at high temperatures and/or high fields––designs, long length processing and properties

Abstract

We show some of the results of production and development of silver-alloy sheathed high temperature superconducting Bi-2223 tapes for applications in power engineering and high magnetic fields (at low temperatures). Depending on the special application tapes with varying designs may be chosen (filament number, alloy of matrix/sheath, twist pitch, cross-section, filling factor, etc.) to meet the requirements of operating current, AC-losses, steepness of voltage–current characteristics, mechanical stresses, etc. The overall critical current density j e of the tapes of long lengths (up to 1300 m) has been improved considerably and the development shows that j e⩾100 A/mm 2 is not the limit even in isotropically strengthened AgMg-alloy Bi-2223 tapes. Furthermore the AC-losses may be reduced effectively by optimizing the processing route and including a twisting step. At low temperatures and high magnetic fields Bi-2223 tapes show high values of j e, too-nearly as high or even higher than Bi-2212 tapes. The dependence of j e( B) in high magnetic fields B is only very small and even the n-values as a measure for the steepness of the voltage–current characteristics do not depend on B. In addition this n-value is higher than for Nb 3Sn-superconductors in high magnetic fields allowing the development of magnets operated in persistent mode.