Effect of Diameter of Nb₃Sn-Based Internal-Tin Wires on the Structure of Superconducting Layers

In the present study the structure and morphology of the Nb3Sn grains in experimental samples of internal-tin (IT) wires with a distributed diffusion barrier and different wire diameters have been studied by SEM and TEM. The results of these studies demonstrate the strong dependence of the fraction of subelements with residual niobium and cavities in tin sources, as well as the average grain size and composition of Nb3Sn phase on the diameter of strands (1.0 mm, 0.7 mm, and 0.5 mm). The results of the analysis of the microstructure help to choose the optimal diameter of strands and show the ways to increase J(c) to a required level for high-field applications.