Advances in low-loss Nb-Ti strand and cable

The new fast ramping accelerators will require NbTi conductors with lower ac losses than hitherto. Finer filaments will be needed, which will demand significant improvements in the double stack production process. Eddy current coupling between filaments within the wire must be reduced by increasing the transverse resistivity across the matrix, but this increase must be achieved without increasing the longitudinal resistivity too much. Coupling within cables must be reduced without impeding current sharing between strands. Cored cables offer the best way of achieving this compromise.