Lap joint resistance and intrinsic critical current measurements on a NbTi superconducting wire

The lap joint resistance between two Cu:Nb-Ti wires (rectangular cross section, 0.53 × 0.68 mm) was measured at 4 K as a function of current, magnetic field and joint area (0.5 to 7 mm²). A simple model, using the magnetoresistance and current dependence, allowed the Joint interface resistance and the current transfer resistance to be separated. The critical current of the wire was also measured adjacent to the Joint. These critical current data were compared with data taken on the control sample (no lap joint). From these comparisons operational checks were deduced for an intrinsic measurement of the critical current adjacent to a joint. The operational checks were on the reversibility of the V-I curves and on their current ramp-rate dependence. When these operational checks were applied to the critical current data of all the joints tested, the results agreed to ±2%.