A model for J/sub c/ in granular A-15 superconductors

The A-15 superconductors, specifically Nb/sub 3/Sn, appear to be the best candidates for the next generation of high-field accelerator magnets. In order for these materials to be successfully employed in future magnets, a better understanding of their transport and magnetization properties must first be obtained. In this paper, a model is presented for the critical current density J/sub C/ in a granular A-15 superconductor. The model is based on previous results for Josephson-coupled arrays, and anisotropic flux pinning by grain boundaries. It is shown that, contrary to what has previously been thought, the observed field dependence of J/sub C/ can be explained without having to invoke a flux-shearing mechanism.