Anomalous switching phenomenon in critical-current measurements when using conductive mandrels

NIST and other laboratories have observed an anomalous switching phenomenon that can occur in critical-current measurements of coiled Nb-Ti and Nb/sub 3/Sn superconductors when mounted on an electrically-conductive measurement mandrel. During acquisition of the voltage-current (V-I) characteristic, large voltage discontinuities are observed, This switching phenomenon results in a multivalued V-I curve, and apparently multiple "critical current" values, An explanation of this phenomenon, some necessary conditions for the switching to occur, as well as methods of detecting the phenomenon are given.<
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