Multifilamentary NbTi superconducting wires for a.c. use were developed by introducing ultrafine Nb island-type artificial pinning centres. The maximum Jc value obtained for wire with a filament diameter of 0.4 μm reached as high as 1.07 × 1010 A m-2 at 1 T and 4.44 × 109 A m-2 at 3 T, which are more than twice the Jc values for conventional wires for a.c. use. For these wires, the constants of the scaling rule for global pinning force, Fp α bγ(1-b)δ, became γ = 0.8 and δ = 1.6. This indicates that the pinning characteristics of the present wires were shifted to the oversaturation-type by the introduction of artificial pinning centres, while they are of the saturation-type for conventional a.c. wires. As a result, the global pinning force at low and medium magnetic fields can be explained fairly well by the direct summation model which is available only for strong pins. A helpful guideline in designing Jc values for a.c. wires is also discussed.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physics and Astronomy(all)