Effect of Strand Damage in Nb3Sn Rutherford Cables on the Quench Propagation in Accelerator Magnets

Accelerator magnets employing Nb$_3$Sn Rutherford cables are more susceptible to conductor degradation than Nb-Ti magnets. Recent measurements on a Nb$_3$Sn accelerator magnet have revealed unexpected behaviour such as decaying voltages at constant current plateaus of V-I measurements, inverse ramp rate and temperature dependence of quench currents, and anomalous quench propagation measured by so-called quench antennas. Numerical modelling has shown that these anomalies can be explained by an inhomogeneous degradation in the Rutherford cable, in which a subset of strands is fully or partially degraded. In this paper, we study how this type of degradation can affect the early stages of quench propagation. With the aid of a network model, we show how quench antenna signals can be used to diagnose inhomogeneous conductor degradation in the Rutherford cable.