IMPROVEMENT OF CRITICAL-CURRENT DENSITY AND RESIDUAL RESISTIVITY ON JELLY-ROLL PROCESSED NB3AL SUPERCONDUCTING WIRES

The residual resistivity of copper stabilizer (rho), is deteriorated b y the diffusion of chromium plated on the strand surface during heatin g of Nb3Al strands. To improve this degradation, the copper stabilizer has been located on the center of the cross-section of the strand rat her than near the strand surface. As a result, rho is improved to one- sixth of previous value achieving 1.6x10(-10)Omega m in a laboratory s cale strand. The critical current density (Jc) of this strand was 715 A/mm(2) at 12T. This technique was applied to prototype strands to be used in a Nb3Al Insert Coil developed in ITER R&D programme resulting in a rho of 1.5x10(-10) Omega m, which meets ITER specification. In ad dition, the improvement of Jc was also studied by a two-stage reaction including a continuous heating procedure, which resulted in a Jc of 1 130 A/mm(2) at 12T and good longitudinal uniformity.