Effects of inhomogeneities on pinning force scaling in Nb3Sn wires

Abstract

We analyzed the effects of A-15 phase inhomogeneities, in particular Sn concentration gradients,on the pinning force scaling behavior ofNbSn3wires. This was accomplished using a softwarecode capable of simulating both magnetization and transport measurements on wires containingsub-elements with an arbitrary(e.g. modeled after EDX data)Sn concentration profile. Wedemonstrate that certain experimentally observed deviations from the ideal scaling behavior, inparticular large values of the high-field scaling exponentqand the zero-temperature scalingfield*()B0c2are caused by gradients in stoichiometry. In the presence of such gradients the scalinganalysis results depend on thefield and temperature ranges covered by the input data, and wediscuss the stronger influence of inhomogeneities on magnetometry-based results. Oursimulation code was benchmarked by attempting to mimic the scaling behavior of a Ti-alloyedRestack Rod Process wire observed in magnetometry experiments with afield limit of 7 T. Bycomparison to transport data obtained infields of up to 15 T, we found that the simulationsprovide a significantly better high-fieldJc(B)prediction compared to an extrapolation based onconventional scaling.