Interstrand and AC-loss measurements on Rutherford-type cables for accelerator magnet applications

One of the main issues for particle accelerator magnets is the control of interstrand resistances. Too low resistances result in large coupling currents during ramping, which distort field quality, while too large resistances may prevent current redistribution among cable strands, resulting in degraded quench performance. In this paper, we review a series of interstrand resistance and AC-loss measurements performed on four Rutherford-type cables. The four cables have the same number of strands and similar outer dimensions, corresponding to LHC quadrupole cable specifications. The first cable is made from NbTi strands, coated with silver-tin alloy, the second one is made from bare Nb₃Sn strands, the third one is made also from bare Nb₃ Sn strands but includes a 25-μm-thick stainless steel core between the strand layers, and the last one is made from Nb₃Sn strands plated with chromium. To cross-check the two measurement types and assess their consistency, we compare the coupling-current time constants determined from AC-loss measurements with estimates based on a simple analytical model and relying on measured interstrand resistances