Design Optimization, Cabling and Stability of Large-Diameter High Jc Nb3Sn Wires

In the framework of the High Field Magnets (HFM) program, CERN is developing and qualifying Nb3Sn Rutherford cables to support magnet development towards the requirements of a future energy-frontier collider, using both state-of-the-art commercial wires and experimental wires under development with industrial partners. The trend towards higher current density and larger diameter wires imposes challenges for magneto-thermal stability. In this study, rolling trials and Rutherford cabling have been performed at CERN for two designs of a 1 mm diameter distributed tin Nb3Sn wire produced by KAT, and for 1 mm and 1.1 mm diameter RRP (R) Nb3Sn wires procured from Bruker OST, and the self-field stability and cabling degradation have been analyzed. The 1 mm RRP (R) wire shows significant degradation in I-c and stability on cabling. Although the latter is not expected to impact the performance of research magnets, the potential of heat treatment optimization to improve stability has also been quantified. The distributed tin wire shows substantially poorer stability, but promising indications of low cabling degradation. The influence of wire design characteristics on cabling behavior and stability have been assessed, and the implications for future wire optimization towards high field accelerator magnet applications have been discussed.