Predicting AC loss in practical superconductors

Abstract

Recent progress in the development of methods used to predict AC loss in superconducting conductors is summarized. It is underlined that the loss is just one of the electromagnetic characteristics controlled by the time evolution of magnetic field and current distribution inside the conductor. Powerful methods for the simulation of magnetic flux penetration, like Brandt's method and the method of minimal magnetic energy variation, allow us to model the interaction of the conductor with an external magnetic field or a transport current, or with both of them. The case of a coincident action of AC field and AC transport current is of prime importance for practical applications. Numerical simulation methods allow us to expand the prediction range from simplified shapes like a (infinitely high) slab or (infinitely thin) strip to more realistic forms like strips with finite rectangular or elliptic cross-section. Another substantial feature of these methods is that the real composite structure containing an array of superconducting filaments can be taken into account. Also, the case of a ferromagnetic matrix can be considered, with the simulations showing a dramatic impact on the local field. In all these circumstances, it is possible to indicate how the AC loss can be reduced by a proper architecture of the composite. On the other hand, the multifilamentary arrangement brings about a presence of coupling currents and coupling loss. Simulation of this phenomenon requires 3D formulation with corresponding growth of the problem complexity and computation time.

Computation of Losses in HTS Under the Action of Varying Magnetic Fields and Currents

“…Coupling loss simulations that take into account the real conductor geometry need in general to be performed with models having three spatial dimensions [257]. Important characteristics for the simulations that represent real world cases are at a minimum the modeling of superconducting domain, of the normal metal matrix and of the contact resistances between these two [258], [256].…”

Hysteretic ac loss of superconducting strips simultaneously exposed to ac transport current and phase-different ac magnetic field

“…Note that the experimental Q can be maximum ͑minimum͒ when 0 0 ͑ 0 /2͒, as reported in Refs. [17][18][19]. The reason for the shifts in 0 for maximum and minimum Q is that the ac magnetic field was large ͑i.e., h 0 Ͼ 1͒ in those measurements.…”

Magnetic field distributions around superconducting strips on ferromagnetic substrates

“…2,3 The magnetic behavior of ferromagnetic substrates can strongly affect the electromagnetic response of superconducting coated conductors. Although the effects of ferromagnetic substrates on ac losses of superconducting coated conductors have been extensively investigated experimentally and numerically, [4][5][6][7][8][9][10][11][12][13] ac losses in superconducting strips on ferromagnetic substrates have not been investigated analytically. Genenko et al 14 analytically investigated the magnetic field and current distributions in superconducting strips surrounded by soft magnets, but they did not consider realistic geometries similar to those of coated conductors.…”