Fabrication and properties of PIT Nb-Al and Nb-Sn based superconductors

Multifilamentary PIT Nb-Al and Nb-Sn strands have been fabricated and tested. Three main conductor variants were investigated; Nb₃Al, Tube-Wall-Reaction (TWR) Nb₃Sn, and Internal Reaction (IR) Nb₃Sn. Multifilament restacks of 7, 19, 30, and 37 filaments were fabricated and tested. The powders were formed by mechanical alloying in a planetary mill with subsequent jet milling for particle refinement. In the case of Nb₃Al, ductile Al was added to the intermetallic compound before filling; while for Nb₃Sn based conductors, Cu was added. All Nb₃Sn strands were alloyed with Ta. Phase formation and transport properties are described. In the case of TWR Nb₃Sn strands, the nature and thickness of the reaction layer was investigated. For monofilaments, the reaction layer was roughly 50 μm thick, for 37 filament strands it was only 5 μm. SC layer J_c values of 2680 A/mm² at 12 T were obtained, but quench limited because of the short samples used in the present work.