Flux pinning in bronze-processed Nb3Sn

Superconducting critical currents have been measured at 4.2 0K and applied magnetic fields up to H/subc/2 for a series of solid-state processed-Nb3Sn conductors. Variations were made in the alloy content of the matrix and core as well as heat-treatment times at 700 0C to produce a wide range of superconducting critical currents. The pinning-force density, F/subp/ (=J/subc/xB), plotted as a function of reduced field, h (=H/H/subc/2), exhibits a peak, F/subp//sup max/, at a reduced field h/subp/. It is concluded that near the upper limit of pinning density to which the theory applies a sharp increase in F/subp//sup max/ may occur without significant shifts in h/subp/ to lower values. This result is added to the model's prediction for lower pinning-density materials, i.e., when lower values of F/subp//sup max/ increase there is a shift in h/subp/ to smaller values