Enhanced J_c properties in superconducting NbTi composites by introducing Nb artificial pins with a layered structure

High critical current densities (4250 A/mm² at 5 T, 4.2 K, and 15 000 A/mm² at 2 T, 4.2 K) were achieved by using an artificially designed pin structure composed of randomly oriented clusters of Nb/NbTi multilayer in a NbTi composite superconductor (with a round cross section). The maximum values were obtained when the Nb layer thickness was designed to be approximately twice the coherence length in NbTi, where the layer thickness is five to ten times thicker than that of the optimized α-Ti ribbon thickness in a conventional NbTi system.