A15 phase superconductors with high current capacities

Development of Nb3Sn filamentary conductors, produced by the solid diffusion process, was continued, aiming at homogeneous properties over long length. Conductor types with stabilizing copper in the cross section were developed which are suited for cabling to conductors with high current capacities. Cables were made: all of them were fully transposed and highly compacted; length up to 2300 m and currents up to 2300 amps at 10 T and 4.2 K. The reaction conditions for Nb3Sn conductors were investigated. When hydrogen was in the annealing atmosphere, there is a change in the field dependence of the current density. The filament diameter also varies the critical current density. An apparatus was constructed and tested to spool reacted conductors. The conductors were tested on their homogeneous properties in solenoids which were made by the wind and react technique. With a NbTi coil (7 T) in a free bore of 40 mm, 15 T at 4.2 K is attained.