Abstract
We analyzed the effects of A-15 phase inhomogeneities, in particular Sn concentration gradients, on the pinning force scaling behavior of Nb3Sn wires. This was accomplished using a software code capable of simulating both magnetization and transport measurements on wires containing sub-elements with an arbitrary (e.g. modeled after EDX data) Sn concentration profile. We demonstrate that certain experimentally observed deviations from the ideal scaling behavior, in particular large values of the high-field scaling exponent q and the zero-temperature scaling field are caused by gradients in stoichiometry. In the presence of such gradients the scaling analysis results depend on the field and temperature ranges covered by the input data, and we discuss the stronger influence of inhomogeneities on magnetometry-based results. Our simulation code was benchmarked by attempting to mimic the scaling behavior of a Ti-alloyed Restack Rod Process wire observed in magnetometry experiments with a field limit of 7 T. By comparison to transport data obtained in fields of up to 15 T, we found that the simulations provide a significantly better high-field Jc(B) prediction compared to an extrapolation based on conventional scaling.
Highlights
FpiinvneidnegcafodrecseaFgpo,=Fi∣e Btzand JcW∣ oefbbsudpisecrcoovnedreudcttihnagt the volume Nb–Ti andNb–Ta alloys obeys a scaling law, i.e. Fp(B) data obtained at different temperatures can be mapped onto a single curve by a simple transformation [1]
The problem is visualized in figure 3, where transport critical current data are compared to the Jc(B) curve predicted based on the scaling analysis of magnetometry data
In this article we presented a detailed analysis of the effects of A-15 phase inhomogeneities, in particular radial Sn concentration gradients within sub-elements, on the pinning force scaling behavior of Nb3Sn wires, including a discussion on the influence of the experimental procedure
Summary
FpiinvneidnegcafodrecseaFgpo,=Fi∣e Btzand JcW∣ oefbbsudpisecrcoovnedreudcttihnagt the volume Nb–Ti andNb–Ta alloys obeys a scaling law, i.e. Fp(B) data obtained at different temperatures can be mapped onto a single curve by a simple transformation [1]. If the function which normalizes the Fp values to the interval [0, 1], and the function describing the scaling field can be parametrized without mutual dependences, the scaling law is said to be separable [2] Data obtained within a particular temperature and field range can be used to calculate the volume pinning force at temperature and field values outside of this range This is a highly attractive quality in terms of characterization and engineering, which explains the popularity of separable scaling laws, in particular in view of the application of conductors based on Nb3Sn—a material whose scaling behavior has been studied extensively
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