Computing AC losses in stacks of high-temperature superconducting tapes

Abstract

Superconducting tape coils and Roebel cables are often modeled as stacks of parallelsuperconducting tapes carrying the same transport current. We solved, in the infinitelythin approximation, the transport current and magnetization problems for such stacksusing an efficient numerical scheme based on a variational formulation of the Kimcritical-state model. We also refined the anisotropic bulk approximation, introduced byClem et al in order to simplify AC loss estimates for densely packed stacks of many tapes;this was achieved by removing the simplifying a priori assumptions on the current sheetdensity in the subcritical zone and the shape of this zone boundary. Finally, we studied theconvergence of stack problem solutions to the solution of the modified bulk problem. It wasshown that, due to the fast convergence to the anisotropic bulk limit, accurateAC loss estimates for stacks of hundreds of tapes can usually be obtained alsousing a properly rescaled model of a stack containing only ten to twenty tapes.