Transverse stress effect on the critical current of internal tin and bronze process Nb{sub 3}Sn superconductors

The effect of transverse stress on the critical current density, J{sub c}, has been shown to be significant in bronze process Nb{sub 3}Sn, with the onset of significant degradation at about 50 Mpa. In an applied field of 10 T, the magnitude of the effect is about seven times larger for transverse stress than for axial tensile stress. In a subsequent study, similar results were observed in another bronze process Nb{sub 3}Sn conductor made by a different manufacturer. The mechanism accounting for the transverse stress effect and its large magnitude compared with the axial tensile effect is still the subject of speculation. In an attempt to better understand the nature of the effect, The authors have undertaken a series of experiments to determine whether the transverse stress effect depends on the grain morphology of the Nb{sub 3}Sn reaction layer in the superconductor. To do this, the authors have measured the effect in an internal tin conductor with excess tin, which yields a more equiaxed Nb{sub 3}Sn grain morphology than for bronze process Nb{sub 3}Sn, where the grains are more columnar. The results for the effect of transverse compression on the J{sub c} of a round bronze process Nb{sub 3}Sn wire are given. The data are probably applicable to a wide variety of Nb{sub 3}Sn conductors for magnet engineering