Radiation-enhanced diffusion growth of Nb3Sn monofilaments: Grain-size effects on critical-current density

Abstract

2-MeV electron irradiation of Nb cores in Cu-Sn bronze matrixes has produced A15 Nb3Sn layers for irradiation temperatures between 290 and 500 °C. Growth of layers at these temperatures (below those for which Nb3Sn is reacted thermally) results in critical-current densities that are higher than those of thermally produced specimens. Analysis of critical-current–vs–applied-field measurements shows that the increased critical-current density is consistent with smaller grain sizes in the lower-temperature enhanced diffusion grown Nb3Sn. Although this is due in part to reduced grain growth at lower temperatures, the possibility of radiation-enhanced grain nucleation is also considered. This is the first demonstration that enhanced diffusion can be used to grow a layer of material at the interface of two dissimilar metals, the new layer being an entirely different crystal structure from the constituents forming the interface.