Critical current versus strain measurement up to 21 T and 1000 A of long length superconducting wires and tapes

A device has been developed to measure the critical current of long length superconductors under uniaxial strain up to 1000 A and up to 21 T . The latter is based on a modified Walters spring (WASP) where zero applied strain can be precisely controlled. The length of the investigated conductor is on the order of 1 m with a typical gauge length between the voltage taps of about 0.5 m . This facilitates the measurement of critical currents at an electric field criterion as low as 0.01 μ V ∕ cm , which is particularly important for superconductors to be used in magnets which are operated in the persistent mode. The operation of the WASP was simulated by finite element calculations indicating that the radial stress (contact pressure) of the superconductor is less than 5% of the axial stress. The performance of the probe is demonstrated for several Nb 3 Sn conductors with round and rectangular cross section, respectively, as well as for a Bi-2223 tape.