High temperature superconductors (HTSs) are enablers of extensive electrification for aircraft propulsion. Indeed, if used in electrical machines, HTS materials can drastically improve their performance in terms of the power-to-weight ratio. Among the different topologies of superconducting electrical machines, a flux modulation machine based on HTS bulks is of interest for its compactness and light weight. Such a machine is proposed in the FROST (Flux-barrier Rotating Superconducting Topology) project led by Airbus to develop new technologies as part of their decarbonization goals driven by international policies. The rotor of the machine will house large ring-segment-shaped HTS bulks in order to increase the output power. However, the properties of those bulks are scarcely known and have barely been investigated in the literature. In this context, the present work aims to fill out partially this scarcity within the framework of FROST. Thus, a thorough characterisation of the performances and homogeneity of 11 large REBaCuO bulks was carried out. Ten of the bulks are to be utilized in the machine prototype, originally keeping the eleventh bulk as a spare. A first set of characterisation was conducted on the eleven bulks. For this set, the trapped field mapping and the critical current were estimated. Then, a series of in-depth characterisations on the eleventh bulk followed. It included critical current measurement, X-ray diffraction, and scanning electron microscopy on different millimetre-size samples cut out from the bulk at various locations. The X-ray diffraction and scanning electron microscopy showed weakly oxygenated regions inside the bulk explaining the local drop or loss in superconducting properties. The objective was to determine the causes of the inhomogeneities found in the trapped field measured on all the bulks, sacrificing one of them, here the spare one. To help obtain a clearer picture, a numerical model was then elaborated to reproduce the field map of the eleventh bulk using the experimental data obtained from the characterisation of its various small samples. It is concluded that further characterisations, including the statistics on various bulks, are still needed to understand the underlying reasons for inhomogeneity in the trapped field. Nonetheless, all the bulks presented enough current density to be usable in the construction of the proposed machine.

This article presents the superconducting machine demonstrator realized within the frame of project FROST (Flux-barrier Rotating Superconducting Topology) which started in 2020. This demonstrator is a 250 kW partially superconducting machine adopting the so-called flux modulation topology which employs a superconducting static coil fed with DC current to produce a magnetic field which is modulated by a rotor composed of superconducting bulks. Both these components are the machine inductor which generate a torque by interacting with a three-phase conventional copper wound armature. This article presents the machine expected performances as well as an overview of the demonstrator assembly.

This paper presents numerical and experimental investigations of the structural control of multilayer high temperature superconducting tapes, using eddy current thermography at room temperature. A rotating magnet wheel is used as inductor to avoid the thermal disturbance of current supplied inductors. A 3-D magnetothermal modeling approach based on an integro-differential formulation in terms of the electric vector potential is developed for eddy current computation in the HTS tapes; associated to a thermal modeling using the finite difference method. The source magnetic field is calculated using the magnetic surface charge model. The simulation results are confirmed by the measurements, both highlighting the potential of such control to detect structural defects such as delamination.

This paper presents a numerical and experimental studies on the non-destructive testing of high temperature superconducting (HTS) multilayer tapes at room temperature, by eddy current thermography (ECT). An experimental setup is developed in which a rotating magnet wheel inductor is used instead of electromagnetic inductors to avoid the inherent thermal disturbance. A 3-D magnetothermal modelling approach is developed for the verification of the experimental results and the simulation of situations that cannot be reproduced experimentally, in particular the verification of the detection limits as a function of the shape and location of the defects. Simulation and experimental results are in good agreement.

Les travaux de recherche menés dans le cadre cette thèse concernent la caractérisation de défauts structurels, à température ambiante, dans les rubans supraconducteurs de deuxième génération, dans une démarche contrôle de qualité et de fiabilité. Dans un premier temps, une modélisation magnétothermique bidimensionnel a été développée pour étudier la possibilité d'appliquer le contrôle par thermographie inductive sur les rubans SHT-2G. Par la suite, un banc expérimental est confectionné pour le contrôle des défauts structurels dans les rubans SHT-2G où un inducteur tournant a été préféré aux inducteurs alimentés par des courants afin d'éviter la perturbation thermique générées par ces derniers. Les mesures expérimentales sont soutenues par une modélisation tridimensionnelle à la fois pour des fins de validation mais aussi pour simuler des situations qui ne peuvent pas être reproduites expérimentalement. Le calcul des courants induits dans le ruban SHT-2G, est basé sur une formulation intégro-différentielle en termes de potentiel vecteur électrique, tandis que le champ magnétique source, créé par les aimants tournants, est calculé en utilisant le modèle de charges magnétiques surfaciques. Un modèle thermique, basé sur la méthode des différences finies, est associé au modèle électromagnétique pour le calcul de la température à la surface des échantillons inspectés. Plusieurs types de défauts sont caractérisés numériquement et expérimentalement. Enfin, une évaluation des contraintes mécaniques, générées par la rotation de la roue aimantée dans les rubans inspectés, est effectuée.