Dynamic response of the ITER vacuum vessel to electromagnetic loads during VDEs

During vertical displacement events (VDEs) plasma halo currents can flow partly through the passive structure. Additionally induced currents occur in the passive structure. Due to these electrical currents, major electromagnetic forces act on the passive structures and hence on the vacuum vessel (VV). As these forces change in time the vessel response is dynamic. This response determines important design drivers such as the reaction forces at the vessel supports, the vessel displacements and stress levels in the vessel structure, and it affects all components attached to the vessel. It is expected that the most severe dynamic response of the vessel occurs during asymmetric VDEs with slow current quench. Experiments on existing tokamak machines have shown that asymmetric loads can rotate around the vertical machine axis. This possible rotation is considered here. Using the finite element (FE) method the dynamic response of the vessel was analyzed in full transient dynamic analyses for the worst case VDEs according to the ITER VV load specification. A 360° FE model of the VV is used since the loads are partly asymmetric. One major difficulty in this assessment was to predict how the sideways load is shared between three simultaneously acting support types. Attention was therefore given to the modeling of the VV supports including the coupling effect with the toroidal magnetic field.