Electromagnetic analysis activities in support of the Breeding Blanket during the DEMO Pre-Conceptual Design Phase: Methodology and main results

During the DEMO Pre-Conceptual Design Phase, a strong effort has been made within the EUROFusion Consortium to define a methodology for the implementation of consistent electromagnetic (EM) analyses on the Breeding Blanket (BB) system, being EM loads during normal and off-normal operations an important input for its structural assessment. Due to the complexity of the considered system, EM loads are evaluated using EM codes (e.g. ANSYS Emag, MAXWELL, CARIDDI) that rely on various numerical modeling approaches. However, independent from the used code, the evaluation of the EM loads in tokamak reactors is not straightforward and must to cope with different problems: the implementation of all sources of magnetic field (in particular the plasma during its evolution); the identification of conductive structures that contribute to the behavior of the eddy currents inside the region of interest; a reasonable simplification of the implemented model to reduce the computation time. This work aims to give an overview of the EM methodology applied to the BB structure analyzing the impact of the used assumptions and simplifications. Particular attention is given to the EM loads generated during plasma instabilities that give rise to severe electromagnetic transients characterized by a fast variation of toroidal and poloidal flux. The contribution of ferromagnetic materials, as well as induced (eddy and halo) currents and electrical contacts with VV, are reviewed identifying, when possible, the qualitative behavior and main parameters that determine the magnitude of the generated EM loads.