Ultra-Fine Nb₃Al Mono-Core Wires and Cables

Jelly-roll (JR) processed wires using metal thin foils as starting materials have excellent cold workability and drawability. We have successfully fabricated Nb/Al composite mono-core wires having 50 μm in outer diameter and over 400 meters in length. Furthermore, some of the wires were additionally drawn to 30 μm in outer diameter. It is known that the critical current density (Jc) of Nb3Al synthesized by low-temperature diffusion reactions increases with decreasing the diffusion distance between Nb and Al. In this study, we have confirmed that Jc would increase with decreasing the wire diameter, and the maximum Jc has been obtained on Nb3Al wires with 30 μm in diameter. In addition, a 7-wire round cable has also been demonstrated using 80 μm diameter wire, with an Ic 7 times the Ic of a single wire. A transport current test was performed for the cable sample simulating W&R and R&W processes using a 50 mm diameter G10 holder. There were no differences between the Ic and the n-values in the W&R and R&W processes. Moreover, as a feasibility study, a 3rd bundle Rutherford cable has been successfully fabricated using 3,108 pure copper wires 50 μm in diameter.