Importance of local stresses and strains during the fabrication of Nb3Sn composite superconductors

The evolution of the distribution of strains and stresses within the multifilamentary composites designed for an improved bronze route is characterized all along their restack bundling process of fabrication. The results of numerous investigations of the microstructure are briefly compared to those of finite element simulations. The work compares the effects of the difference in mechanical behaviour of the various components to that of their repartition. The importance of the composite lay-out, that is to say of the relative disposition and of the volume of the bronze areas, as well as of the size, morphology and spacing of the filaments, for the Nb3Sn formation is demonstrated. The consequences for both the Nb3Sn grain size and the critical current are finally displayed.