A numerical method is proposed to analyse the electromagnetic behaviour of systems including high-temperature superconductors (HTSCs) in time-varying external fields and superconducting cables carrying AC transport current. The E-J constitutive law together with an H-formulation is used to calculate the current distribution and electromagnetic fields in HTSCs, and the magnetization of HTSCs; then the forces in the interaction between the electromagnet and the superconductor and the AC loss of the superconducting cable can be obtained. This numerical method is based on solving the partial differential equations time dependently and is adapted to the commercial finite element software Comsol Multiphysics 3.2. The advantage of this method is to make the modelling of the superconductivity simple, flexible and extendable.

AC loss can be a significant problem for any applications that utilize or produce an AC current or magnetic field, such as an electric machine. The authors investigate the electromagnetic properties of high temperature superconductors with a particular focus on the AC loss in superconducting coils made from YBCO coated conductors for use in an all-superconducting electric machine. This paper presents an improved 2D finite element model for the cross-section of such coils, based on the H formulation. The model is used to calculate the transport AC loss of a racetrack-shaped coil using constant and magnetic field-dependent critical current densities, and the inclusion and exclusion of a magnetic substrate, as found in RABiTS (rolling-assisted biaxially textured substrate) YBCO coated conductors. The coil model is based on the superconducting stator coils used in the University of Cambridge EPEC Superconductivity Group's all-superconducting permanent magnet synchronous motor design. To validate the modeling results, the transport AC loss of a stator coil is measured using an electrical method based on inductive compensation by means of a variable mutual inductance. Finally, the implications of the findings on the performance of the motor are discussed.

Crossed-magnetic-field effects on bulk high-temperature superconductors have been studied both experimentally and numerically. The sample geometry investigated involves finite-size effects along both ͑crossed-͒ magnetic-field directions. The experiments were carried out on bulk melt-processed Y-Ba-Cu-O single domains that had been premagnetized with the applied field parallel to their shortest direction ͑i.e., the c axis͒ and then subjected to several cycles of the application of a transverse magnetic field parallel to the sample ab plane. The magnetic properties were measured using orthogonal pickup coils, a Hall probe placed against the sample surface, and magneto-optical imaging. We show that all principal features of the experimental data can be reproduced qualitatively using a two-dimensional finite-element numerical model based on an E-J power law and in which the current density flows perpendicularly to the plane within which the two components of magnetic field are varied. The results of this study suggest that the suppression of the magnetic moment under the action of a transverse field can be predicted successfully by ignoring the existence of flux-free configurations or flux-cutting effects. These investigations show that the observed decay in magnetization results from the intricate modification of current distribution within the sample cross section. The current amplitude is altered significantly only if a field-dependent critical current density J c ͑B͒ is assumed. Our model is shown to be quite appropriate to describe the cross-flow effects in bulk superconductors. It is also shown that this model does not predict any saturation of the magnetic induction, even after a large number ͑ϳ100͒ of transverse field cycles. These features are shown to be consistent with the experimental data.

The development and application of second generation high temperature superconducting (2G-HTS) tapes have attracted much attention in China recently. Progress in upscaling high performance 2G-HTS tape production at Shanghai Superconductor Technology (SST) is reported in this paper. With ion beam assisted deposition, biaxially textured buffer layers with a configuration of CeO 2 /LaMnO 3 /MgO/Y 2 O 3 /Al 2 O 3 /C-276 have successfully been fabricated. In-plane and out-ofplane texture degrees of CeO 2 films achieve 2°-4°and 2°, respectively. A multi-plume multi-turn pulsed laser deposition (PLD) system combined with the so-called 'radiation assisted conductive heater' has been proposed and further developed for REBCO layer deposition. Our effort was focused on minimizing the temperature variations in the deposition region by modifying the heating shield that assists the conductive heater of the drum-like cylinder. A tape travelling speed of 100-180 m h −1 can be achieved with a steady temperature profile when passing through the deposition zone, which is very beneficial for the growth of the REBCO layer. Taking advantage of the liquid phase growth mode, several compositions of superconducting films with a thickness in the range of 1-2.5 μm have been grown with high growth rates of over 40 nm s −1 . Furthermore, the microstructures and superconducting performance were investigated in detail. Based on these studies, superconducting tapes with piece lengths of up to 500 meters have been developed. High I c values at 77 K, self-field (over 520 A cm −1 width) or at low temperature, high magnetic field conditions (over 560 A/4 mm width at 4.2 K, 10 T, perpendicular field) have been achieved. Lamination and jointing techniques have also been developed by SST for power and magnet applications.

PurposeThe purpose of the paper is to provide a comparison of first‐ and second‐order two dimensional finite element models for evaluating the electromagnetic properties and calculating AC loss in high‐temperature superconductor (HTS) coated conductors.Design/methodology/approachThe models are based on the two‐dimensional (2D) H formulation, which is based on directly solving the magnetic field components in 2D. Two models – one with a minimum symmetric triangular mesh and one with a single‐layer square mesh – are compared based on different types of mesh elements: first‐order (Lagrange – linear) and second‐order (Lagrange – quadratic) mesh elements, and edge elements.FindingsThe number and type of mesh elements are critically important to obtain the minimum level of discretization to achieve accurate results. Artificially increasing the superconductor layer and choosing a minimum symmetric mesh with triangular edge elements can provide a sufficiently accurate estimation of the hysteretic superconductor loss for a transport current.Originality/valueThis paper describes how the selection of mesh type and number of elements affects the computation speed and convergence properties of the finite element model using two different types of meshing. It offers an insight into the different factors modelers must consider when modeling HTS coated conductors and the methods that may be applied when extending the model to complex device geometries, such as wound coils.