Frank-Read source-activated flux shear in type-II superconductors

Abstract

An expression is derived for the flux-pinning force density Fp as a function of magnetic induction B and pinning defect center density ρ, based on a model of flux-line-lattice shear activated by Frank-Read source dislocations. Fp(b) peak positions shift with increasing ρ to larger b, where b=B/Bc2 is the reduced induction and Bc2 is the upper critical field. For a given B there exists an optimum defect center density, ρopt, for which Fp becomes a maximum. The potential Fp enhancement is a function of the initial defect concentration ρi. At a constant B a larger Fp increase is obtained for smaller ρi, and at a constant ρi the increase is larger for larger B. Quantitative agreement for neutron-irradiated Nb3Sn is obtained by fitting Fp(b) data with three parameters ρi, a pinning defect center generating linear rate constant α, and the third consisting of a function of the Ginzburg-Landau κ and Bc2. The major characteristic of Fp(b) for Nb3Sn, which is Fp peaking at or near b=0.2, is also true for the copper-oxide-based high-Tc superconductors, and the proposed model also applies to these materials.

Source-reported materials — not catalogue approval

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