Progress in Nb₃Sn RRP Strand Studies and Rutherford Cable Development at FNAL

A strong push to Nb3Sn conductor development in the U.S. as well as in Europe has been driven by the development of Nb3Sn dipoles and quadrupoles for the Large Hadron Collider (LHC) luminosity upgrades. Rutherford cables with high aspect ratio are used for these magnets to achieve large fields and gradients at relatively low currents. At Fermilab National Accelerator Laboratory (FNAL), 40-strand keystoned cables with and without a stainless steel core were developed and produced using 0.7-mm Nb3Sn strands made by Oxford Superconducting Technology with 127 and 169 restacks using the Restacked Rod Process with either NbTa alloy or Ti doping. The performance and properties of such strands and cables were studied to evaluate possible candidates for the production magnets of the LHC upgrades. The electrical performance was first compared for wires under flat-rolling deformation and then in cables made with different processes and geometries. The round wires are also compared under tensile and compressive strain using a Walters' spring variable-temperature probe that was recently commissioned at FNAL. Finally, cable test results obtained with a 14 T/16 T Rutherford cable test facility with a bifilar sample and a superconducting transformer are shown.