Critical current measurements of NbTi wires in the temperature range 4.2-1.8 K

The critical currents of several NbTi wires have been measured in boiling helium in the temperature range 4.2-1.8 K and at magnetic fields up to 10T. In some instances, I/sub c/ (defined at a resistivity of 10/sup -14/ ohm) can be measured over the entire temperature range while for other conductors the quench drops below I/sub c/ as the temperature is reduced and the critical current cannot be determined. For most of these strands I/sub c/ can again be measured once the helium bath is in the superfluid state but for some wires it is not possible to measure the effective resistivity even in superfluid. Conductors fabricated by the same manufacturer can exhibit completely different behavior. In general there is a tendency for wires with high intrinsic current density and relatively low copper content to perform erratically at the lower temperature.