Strain scaling law for flux pinning in NbTi, Nb3Sn, Nb-Hf/Cu-Sn-Ga, V3Ga and Nb3Ge

Critical current and flux pinning densities have been determined for a series of practical conductors as a function of uniaxial tensile strain in magnetic fields ranging from 4 T to 19 T. An empirical relation has been found at 4.2 K that accurately describes these data over the entire range of field under both compressive and tensile strain. The pinning force F has been found to obey a scaling law of the form: where f(b) is a function only of the reduced magnetic field , and is the strain dependent upper-critical field determined from high-field critical-current measurements. This strain scaling law was found to hold for all superconductors examined thus far, including commercial multifilamentary wire, mono-filamentary conductors, CVD tapes, extremely fine-filament conductors, partially-reacted specimens, and "in-situ" cast conductors. For Nb3Sn, , for Nb3Sn with Hf and Ga additions, , for V3Ga, , for Nb3Ge, , and for NbTi, . The importance of this relationship is that, for these conductors at least, it is possible to measure F at one strain and then immediately be able to predict F (and thus Jc) at other strain levels simply by scaling the results by . The relation between strain scaling and temperature scaling is discussed as it relates to flux pinning theories.