Simulating the In-Field AC and DC Performance of High-Temperature Superconducting Coils

In this paper, the authors investigate numerically the in-field behavior of high-temperature superconducting (HTS) coils and a method to potentially improve their performance using ferromagnetic material as a flux diverter. The ability to accurately predict the electromagnetic behavior of superconductors in complex geometries and electromagnetic environments is crucial to the design of commercially viable superconductor-based electrical devices, such as power transmission cables, superconducting fault current limiters, transformers, and motors and generators. The analysis is carried out using a 2-D axisymmetric model of a circular pancake coil based on the H-formulation and implemented in Comsol Multiphysics 4.3a. We explore the use of flux diverters to improve an HTS coil's performance with respect to its dc (maximum allowable/critical current) and ac (ac loss) characteristics, for various background magnetic fields. It is found that while flux diverters can improve the ac properties of coils, they can be detrimental to the dc properties in this particular configuration.