Improvement of critical current density and residual resistivity onjelly-roll processed Nb3Al superconducting wires

摘要

The residual resistivity of copper stabilizer (ρ), is deteriorated by the diffusion of chromium plated on the strand surface during heating of Nb3Al strands. To improve this degradation, the copper stabilizer has been located on the center of the cross-section of the strand rather than near the strand surface. As a result, ρ is improved to one-sixth of previous value achieving 1.6×10-10 Ωm in a laboratory scale strand. The critical current density (Jc) of this strand was 715 A/mm2 at 12 T. This technique was applied to prototype strands to be used in a Nb3Al Insert Coil developed in ITER R&D programme resulting in a ρ of 1.5×10-10 Ωm, which meets ITER specification. In addition, the improvement of Jc was also studied by two-stage reaction including a continuous heating procedure, which resulted in a Jc of 1130 A/mm2 at 12 T and good longitudinal uniformity