To achieve further increases in the critical current densities of Nb-Ti ultrafine multi-filamentary superconducting wires for a.c. applications, wires were fabricated in which Nb island-type artificial pinning centres had been designed and introduced into filaments according to flux pinning theory. The changes in pin parameters which accompanied the diameter reduction increased the pinning force density Fp over a wide range of magnetic field, and oversaturation phenomena were observed, with the position of the Fp peak shifting towards the high-field side. High critical current densities Jc were achieved: 1.42 × 1010 A m-2 at 1 T for 0.1 μm filaments, and 8.7 × 109 A m-2 at 2 T and 6.1 × 109 A m-2 at 3 T for 0.4 μm filaments. Furthermore, it was determined that where the correlation length I66 and fluxoid interval af are such that 2I66 < af, the magnetic field at the Fp peak is determined by the pin interval ds. This discovery has given us useful pointers for the design of Nb-Ti superconducting a.c. wires, in terms of Jc, through the introduction of artificial pins.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physics and Astronomy(all)