Criteria for the prevention of filament and wire breaking during the fabrication of multifilamentary composite superconducting wire

This paper deals with the wire breaking problems during the fabrication of the NbTi SSC superconducting wire. The global objective is to establish sound guidelines for the design of the superconductor and of the pass-reduction practices that will lead to the fabrication of high-quality defect-free NbTi SSC superconducting wire in a reproducible cost-effective manner. In larger detail: (a) The geometrical factors of the assembly of the wire need to be analyzed as factors in the success of the fabrication of final small-size filaments without breaks. (b) The ranges of processing parameters (geometric, material strength ratios, and pass-reduction schedules), which lead to successful products without filament breaks, need to be determined analytically. A quantitative criterion for the selection of the range of parameters is needed. Next the structure and definitions associated with composite multifilamentary wire are modeled. The differences between Bi-Metal and Tri-Metal approximations for the SSC superconducting wire are described. It is shown that the Bi-Metal approximation which was successful in treating earlier wire assemblies should be upgraded by the Tri-Metal approximation