Anomalies on V–I characteristic of NbTi cable-in-conduit conductors

Two kinds of anomaly, observed in the Volt–Ampere Characteristic (VAC) of large NbTi cable-in-conduit conductors (CICC) are discussed. In one case, the wavy behavior of the VAC close to the current sharing range is explained with oscillations of the cooling temperature of the order of 10–30 mK. A simulation of periodic temperature variations is done to reproduce the experimental behavior. In another case, voltage spikes in the VAC are correlated with saw-tooth signals from Hall sensors monitoring the conductor self-field, suggesting the occurrence of local quenches and recovery, with local current re-distribution. The analysis of the two kinds of anomaly, with their own signature on the VAC, provides valuable diagnostic tools for the interpretation of large size CICC test results.