Self-field effects on critical current measurements of large multi-strand conductors

We have studied the methods for comparing the values of the critical current measured on superconducting strands with the ones obtained on a complex Rutherford cable made of the same strands. This problem is related to the definition of critical magnetic field for strands and cables carrying a given current, which generates a not negligible and inhomogeneous self-field. The method is based on the evaluation of the electrical field along the conductors carrying currents around the critical value. The developed criteria are adopted for comparing the critical currents measured on short samples of strands and Rutherford cables made of 32 strands embedded in pure aluminum matrix.