Contact Resistance of Stabilized Superconducting Wires

A new method for measuring contact resistance of composite conductors is proposed and some results measured are described of contact resistance and resistance ratio (300°K/4.2°K) of various stabilized superconducting wires. By the method that we formerly proposed, the longitudinal potential variation of conductor with current electrodes suitably attached can be measured by a voltage-probe or terminals, and then contact resistance may be computed from the characteristic value of attenuation. Our stabilized superconducting wires, copper electro-plated wires (NbZr or NbTi) and mechanically bonded wires (NbTi), have a contact resistance of about 0.05μΩ-cm2 which is considerably lower than those of commercially available wires. As for resistance ratio, mechanically bonded wires with O. F. H. C. copper are naturally better than electro-plated wires. The former has resistance ratios of 150-250, while the latter has ratios of 30-100. The formation of a intermetallic compound was sharply detected by this method. A jump in contact resistance was found near the transition temperature of superconductor.