Mechanical impact of electromagnetic transients on the European DEMO divertor. Part 1: Vertical displacement event

Abstract

This paper presents the study of the forces and moments expected on the European DEMO divertor, due to the fast electromagnetic transients associated to plasma instabilities events. A 3D Magneto-Quasi-Static (MQS) model is here adopted to solve such a problem, implemented in Ansys EMAG. A hybrid modelling approach is proposed, that can be placed between a pure global model (where the divertor is modelled along with all the external passive and active components) and a local one, where only the divertor is present in the model and the external world is represented through equivalent boundary conditions (submodelling). Indeed, the model proposed here includes a detailed description of all the divertor components (cassettes, targets, liner, cooling pipes, etc..) and a coarser description of the main passive external components (vessel, blanket, rails, etc..). The active components (coils and plasma currents) are instead replaced by suitable equivalent current sources and by a known equilibrium magnetic field. The analysis is here carried out with reference to one of the most challenging events for the divertor, namely a downward directed Vertical Displacement Event. The forces and moments associated to the whole divertor and to its cooling subsystem are evaluated, and a sensitivity analysis is performed to check the impact of the choice of the materials to be used to realize the supports inside the divertor and between the divertor and the vacuum vessel.