Characterization of a Large Size Co-Extruded Al-Ni Stabilized Nb-Ti Superconducting Cable for Future Detector Magnets

Future detector magnets call for the development of next-generation large-sized Al stabilized Nb-Ti superconducting cables exhibiting high yield strength for coping with the large stress in wide bore magnets with peak magnetic fields up to 6 T, while avoiding significant degradation in residual resistivity ratio. Precipitation type alloys obtained by dilute-alloying of high purity Al with suitable additives like Ni, subjected to partial annealing following cold drawing, can feature a yield strength up to 110 MPa at 4.2 K. For the ATLAS central solenoid, a Nb-Ti cable has been plated with a precipitation-type Al-0.1wt%Ni alloy. However, this conductor with a critical current of 20 kA at 5 T, features a cross-section of only 130 mm². Here, a first step in process scale-up to a 60 kA at 5 T class conductor is described. For the first time, a continuous co-extruded Al-0.1wt %Ni stabilized conductor has been produced with a cross-section as large as 700 mm². Sections of the conductor are work hardened in order to increase the mechanical properties of the as-extruded temper. The mechanical and transport characteristics as a function of the amount of work hardening have been assessed by removing samples after every subsequent step.