Computing AC losses in stacks of high-temperature superconducting tapes

TL;DR

This paper presents an efficient numerical method for calculating AC losses in stacks of high-temperature superconducting tapes, improving accuracy and convergence for densely packed configurations.

Contribution

It introduces a refined anisotropic bulk approximation and demonstrates rapid convergence, enabling accurate AC loss estimates with simplified models.

Findings

Fast convergence of stack solutions to bulk limit

Accurate AC loss estimates with fewer tapes

Refined approximation improves modeling accuracy

Abstract

Roebel cables and superconducting tape coils are often modeled as stacks of parallel superconducting tapes carrying the same transport current. We solved, in the infinitely thin approximation, the transport current and magnetization problems for such stacks using an efficient numerical scheme based on a variational formulation of the Kim critical-state model. We also refined the anisotropic bulk approximation, introduced by Clem et al. in order to simplify AC loss estimates for densely packed stacks of many tapes; this was achieved by removing the simplifying assumptions on the current sheet density in the subcritical zone and the shape of this zone boundary. Finally, we studied convergence of stack problem solutions to the solution of the modified bulk problem. It was shown that, due to the fast convergence to the anisotropic bulk limit, accurate AC loss estimates for stacks of hundreds of tapes can usually be obtained also using a properly rescaled model of a stack containing only ten-twenty tapes.