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

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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.