Flux Pinning Mechanisms in Superconducting A15 Materials and the Optimization of Their Transport Properties
The superconducting properties and microscopic characterization are presented for Nb3Sn, (Nb,Ta)3Sn and (Nb,Ti)3Sn conductors made using several different fabrication routes. The element concentration profiles at the grain boundaries, determined using STEM, leads to a pinning model that includes the pinning by normal boundaries and by the grain boundary flux shear. The use of the shear modulus C66 for all the range of field and temperature does not fit the Kramer theory. Use of a flux pinning effective grain size, Deffective, in the model leads to good agreement. Deffective depends on the magnetic field (flux line spacing), has a smooth behavior at high fields and increases almost exponentially at low fields following the flux line spacing behavior, as expected. The determination and optimization of Deffective leads to the best superconductor current carrying characteristics.
KeywordsMagnetic Field Grain Size Distribution Critical Current Density Flux Line Experimental Behavior
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