Design of a Probe for Strain Sensitivity Studies of Critical Current Densities in Superconducting Wires

The critical current density (J(c)) of brittle superconducting wires used in high field magnets is very sensitive to axial strain. An accurate measurement of this strain dependence at various magnetic fields and temperatures is critical for magnet design and operation. A number of methods and techniques have been used, which generally fall into either the monotonic axial loading or bending spring techniques. The design of a variable-temperature probe to perform strain sensitivity measurements in Helium of both LTS and HTS wires is herein described. The sample is wound and soldered onto a helical Walters' spring device, which is fixed at one end and subjected to a torque at the free end. Both Ti-6Al-4V and CuBe were used as materials for the Walters' spring. Two concentric copper tubes act dually as 2000 A current and 60 Nm torque carriers. The torque is generated via a worm-gear setup and transmitted to the sample through the inner tube and spring assembly.