Contents lists available at ScienceDirect Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes Dynamic behaviour of DEMO vacuum vessel during plasma vertical displacement events F. Giorgetti a , C. Bachmann b , V.G. Belardi c , G. Calabrò a , S. Ciufo a , P. Fanelli a, *, M. Fulici c , F. Maviglia b , S. Minucci a , F. Vivio c a Department of Economy, Engineering, Society and Business Organization (DEIM), University of Tuscia, Largo dell’Università, Viterbo 01100, Italy b EUROfusion Consortium, PPPT Department, Boltzmannstr. 2,Garching, Germany c Department of Enterprise Engineering, University of Rome Tor Vergata, Via del Politecnico, 1, Rome 00133, Italy ARTICLE INFO Keywords: DEMO Vertical displacement events Electromagnetic-mechanical coupling DEMO vacuum vessel Transient analysis ABSTRACT In tokamaks during plasma vertical displacement events (VDEs) electrical currents occur in the vacuum vessel (VV) and in the in-vessel components (IVCs) that interact with the strong magnetic field generating large electromagnetic (EM) loads. The aim of the present work is the evaluation of the peak displacements and ac- celerations of the DEMO VV in case of VDEs. Four types of VDEs are investigated that are specified to generate the most severe net loads. The assessment considers also the electromagnetic-mechanical coupling between the VV and the toroidal field (TF) coils whose characteristic stiffness and damping coefficients were determined through a transient EM analysis. In a second step a transient dynamic analysis was performed using a structural finite element (FE) model of the VV to evaluate the displacement and acceleration peaks during the VDEs in relevant locations of the VV. 1. Introduction Plasma VDEs are some of the most severe load conditions occurring in a tokamak. During a VDE electrical currents can flow in the con- ductive metallic structures and in the VV and the IVCs. These currents cross the magnetic field of the tokamak generating large EM loads that are often design drivers of tokamak components. Two types of currents are postulated to contribute to generate the Lorentz forces in the VV during VDEs: induced eddy currents, flowing mainly in toroidal direc- tion, and non-induced halo currents, flowing in poloidal and toroidal directions. As shown in [1] two different asymmetric effects were observed in tokamaks during asymmetric VDEs: an asymmetric peak of the halo currents and a non-uniform plasma current. The asymmetric VDE loads have been specified for ITER [1]. The dynamic response of ITER VV when subjected to asymmetric VDE loads is assessed in [2] presenting displacements and support reactions for different sets of VDE para- meters, i.e., downward vs. upward VDE and different levels of the asymmetries. The consequent asymmetric loads acing on the VV cause a sideways movement of the VV in the toroidal magnetic field, causing a field variation and consequently a change of the EM loads. The mutual interaction between the VV and the TF coils can be expressed, from a mechanical point of view, as a spring-damper system. A damping coefficient is adopted in [3] for the transient study of the ITER vacuum vessel during asymmetric VDEs. The damping introduced in the 360° electro-mechanical coupled FE model causes a progressive reduction of the system oscillation. As far as DEMO concerns, the VV and different in-vessel compo- nents, with loads arising during VDEs, were subject to preliminary analyses given the current stage of the fusion roadmap [4]. EM loads were preliminarily assessed considering symmetric VDEs on the DEMO divertor [5] and the DEMO water-cooled lead-lithium (WCLL) breeding blanket (BB) [6]. A preliminary static structural analysis of the DEMO VV during VDEs is performed in [7] demonstrating the capability of the VV structure to withstand VDE forces and the VV weight, the VV being supported at the lower VV ports. The present paper evaluates the maximum displacements and acceleration peaks of the DEMO VV at its peripheral ports in case of asymmetric VDEs considering the electro- magnetic-mechanical coupling between the VV and the TF coils. The work is composed of three main analysis: 1. Electromagnetic analysis: a transient electromagnetic analysis is used to obtain the EM loads that arise when the VV moves within the TF coils EM field. https://doi.org/10.1016/j.fusengdes.2020.111876 Received 15 April 2020; Received in revised form 15 June 2020; Accepted 8 July 2020 ⁎ Corresponding author. E-mail address: pierluigi.fanelli@unitus.it (P. Fanelli). Fusion Engineering and Design 159 (2020) 111876 0920-3796/ © 2020 Elsevier B.V. All rights reserved. T