Two methods of AC loss calculation in numerical modelling of superconducting coils

Abstract

Numerical methods are widely utilised in the prediction of AC loss in superconducting coils. A commonly used approach is based on determination of the local dissipation calculated from the distributions of electrical field and current density throughout the winding, as well as its evolution over the AC cycle. This quantity reflects the heat release on a microscopic scale, and its integration throughout the coil winding over one AC cycle provides the value of loss per cycle in the coil. On the other hand, one can look at global quantities characterising the energy flow from a power supply to the coil: the electrical current supplied and the voltage on its terminals. Averaging, with respect to time, of the voltage times current product also gives the coil loss per cycle. Here we show that a comparison of results obtained with ‘local’ and ‘global’ methodologies can be useful in identifying the numerical errors caused by calculation techniques. However, this is possible only when the modelling method allows for determination of the essential physical quantities as independent variables. We illustrate this approach with an example utilising the A-φ and H-formulations for the AC loss evaluation in a ten-turn pancake coil wound from coated conductor tape.