Critical current and n-value modifications from superconducting strands to Rutherford cables

Abstract

Abstract We propose a method for relating the critical current measured on superconducting wires with the one measured on a Rutherford cable made by cabling the same wires. The problem is mainly related to the definition of the critical magnetic field of strands or cables exposed to a non-uniform magnetic field due to the self-field. The field generated by the conductor may be a not negligible fraction of the total applied field, so to play a central role in determining both the measured value of the critical current and the shape of the superconducting transition as observed through voltage–current measurements. In this frame it is important to understand the effect of the inter-strand currents due to the fact that strands in saturated regions can exchange current with not saturated strands. We show how the V – I characteristic would be modified by this effect and what seems to happen in real conductors, by measurements performed on high-current multi-strand cables.