Critical current measurements at electric fields in the pV m/sup -1/ regime

We describe a technique for characterising sample lengths of commercial superconducting wire in closed loop configuration. This enables the measurement of critical current, as a function of applied magnetic field, at electric field criteria in the range 10/sup 6/ to 1 pV m/sup -1/ by detecting the decay of current in the closed loop. How these measurements relate to the more traditional 4 terminal measurements made on short sample coils is discussed and representative data from both NbTi and Nb/sub 3/Sn samples are presented and analysed.