The effect of strain upon the scaling law for flux pinning in bronze process Nb3Sn

The semiempirical scaling law for flux pinning, Fp=ABnc2bl (1−b)m has been tested for bronze process Nb3Sn conductors under uniaxial tension. The dependences of the bulk pinning force Fp on the upper critical field Bc2 and the reduced field, b=B/Bc2, were weakly affected by strain. However, the factor A, which depends on the number and strength of the pinning centers, and on the Ginzburg-Landau parameter κ decreased by more than a factor of 20 when the compressive prestrain on the Nb3Sn was removed by application of external stress. The variations of Tc and Bc2 with strain suggest that the change in κ is not sufficient to account for the change in A. Therefore, it is probable that strain induces microstructural changes which affect the number and/or strength of the pinning centers.