Enhanced high-field current carrying capacities and pinning behavior of NbTi-based superconducting alloys

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Abstract
High-field critical current densities Jc and pinning behavior are discussed for Nb-63a/oTi, Nb-61.7a/oTi-3a/oHf, and Nb-64.7a/oTi-7.2a/oTa superconducting alloys. Jc properties for 8–12 T in these alloy superconductors under superfluid helium environments can be even superior to those in Nb3Sn at 4.2 K, when they are heavily cold-worked after final heat treatments. A temperature scaling law of the flux pinning force Fp is found to hold for these alloys in the form of FP=K [Bc2(T)]nbp(1−b)q, where Bc2 is the upper critical field and b≡B/Bc2. The peak reduced field, bm, in the Fp−b curve depends upon how the alloys have been processed. The origins of n, p, and q are discussed in terms of the processing condition.