A probe for investigating the effects of temperature, strain, and magnetic field on transport critical currents in superconducting wires and tapes

A variable-temperature probe has been developed to study the effect of strain on the transport properties of superconducting wires and tapes in high magnetic fields. The strain is applied to the wire by soldering it to a thick coiled spring and twisting one end of the spring with respect to the other. Strain can be applied reversibly from −0.7% to +0.7%. Measurements can be performed either in (pumped) cryogen or under vacuum. When immersed in liquid helium at 4.2 K, the probe can carry at least 200 A. From 6 to 16 K, with thin (low-loss) current leads the temperature of the sample is stable to ±45 mK for currents around 15 A, and to ±100 mK for currents around 25 A. With thick current leads, ±10 mK stability is achieved for currents up to 85 A. Full details of the probe design are described. Results obtained for a bronze processed niobium–tin multifilamentary wire are presented.