A macroscopic model for coupling current losses in cables made of multistages of superconducting strands and its experimental validation

In a multistage cable the superconducting strands occupy the whole volume in a complex oscillatory pattern from the axis to the periphery. After considerations on the trajectories of the strands, it is shown that the cable can be organized in a multizone structure with time constants determined from the basic time constants of the various cabling stages. The effective volume fractions of the cable in which losses can be evaluated are also derived. The model is assessed by a fit of an experimental curve. In the case under consideration, the screening effects are relatively limited. Altogether, the cable is well characterized by very few parameters: a series of in sequence time constants associated to small fractions of volume. The model is then used to evaluate losses in various conditions of field variations.