Assessment of dynamic response of a DEMO divertor under electromagnetic impact loads. Part 1: A computational methodology for a cost-effective analysis

This paper reports on a FEM-based computational methodology to assess dynamic amplification factors (DAF) of a divertor cassette, under electromagnetic (EM) impact loads caused by a plasma disruption event. The investigation concerns a typical divertor cassette body (CB) of the European DEMO reactor (baseline model of year 2022). The modal behaviour of the CB structure is analysed first, followed by a full transient dynamic analysis as determined by a transient dynamic loading, finally the resulting deformation and stress response is computed. Furthermore, a post-processing visualisation tool is developed, in order to graphically display the spatial and temporal evolution of EM forces distribution induced in the structure, which allows analysts to get an in-depth understanding of the relationship between the (local and global) dynamic response of the system and the induced EM forces, over the entire transient time scale. Finally, a spatial and temporal map of EM forces, stress and deformation amplification due to the dynamic/inertia effects are produced. The proposed methodology enables structural analysts to employ a cost-effective (from a computational point of view) static simulation for stress calculation even for a dynamic EM impact loading case, taking fully into account inertia effects once the equivalent static loads are properly calibrated with DAF values. The aims of the present paper are two-fold: 1) to present the entire procedure of the methodology using a divertor CB as an example and 2) to demonstrate the benefits of the approach, particularly for an iterative design optimisation stage, and the usefulness of the graphical visualization tool. Overall (spatial and temporal) maximum stress/deformation responses are estimated by means of the DAFbased static analysis method, for selected EM impact loads that are relevant for plasma disruption events in a DEMO reactor. This study shows: 1) how sensitive is the dynamic response (in terms of resulting stress and deformation) of the divertor system when affected by local design changes (e.g. geometry of supports) and 2) how efficiently a dynamic loading problem can be replaced by an equivalent static analysis, gaining reliable information on model responses.