Influence of Production Parameters on the Superconducting Properties of Nbti and Nb$n Wires

The commercial specification of superconducting NbTi and Nb,Sn composite wires is normally given by a few numbers : I,(p,B,T), n, RRR, wire and filament diameter and twist length. To some extent their values cannot be chosen independently, nor do they guarantee proper operation of the system in all aspects, for instance fields in dipoles for accelerators. For Nb,Sn composites, depending on the production process, an extra set of parameters describing the stress sensitivity seems to be needed to specify the quality of the composite. More intriguing is the situation for Nb,Sn. Here the same set of parameters is used as for NbTi, but due to the large difference in production processes, the reaction heat treatment, the mechanical properties of the final product and the higher fields of applications additional specifications seem necessary. Furthermore, it seems that the production method of the wires leads to products with different quality. Whether this is necessarily so is not systematically investigated, but some differences will be outlined below. These variations will add up in reducing the performance of the superconducting composite to those resulting from geometrical sources already present in NbTi, where larger uniformity in the results of the treatment can be achieved.