مرکز منطقه ای اطلاع رساني علوم و فناوري - Strain scaling law for flux pinning in NbTi, Nb<inf>3</inf>Sn, Nb-Hf/Cu-Sn-Ga, V<inf>3</inf>Ga and Nb<inf>3</inf>Ge

Abstract :

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: $F = [B*_{c2}(\\varepsilon )]^{n} f(b)$ where f(b) is a function only of the reduced magnetic field $b \\equiv B/B*_{c2}$ , and $B*_{c2}$ 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, $n \\cong 1.0$ , for Nb3Sn with Hf and Ga additions, $n \\cong 1.2$ , for V3Ga, $n \\cong 1.4$ , for Nb3Ge, $n \\cong 1.6$ , and for NbTi, $n \\cong 4$ . 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 $[B*_{c2}(\\varepsilon )]^{n}$ . The relation between strain scaling and temperature scaling is discussed as it relates to flux pinning theories.