Fusion Engineering and Design 159 (2020) 111948 Available online 8 September 2020 0920-3796/© 2020 Published by Elsevier B.V. TFC-PREDIM: A FE dimensioning procedure for the TF coil system of a DEMO tokamak reactor Ilia Ivashov *, Wolfgang Biel, Philippe Mertens Institut für Energie und Klimaforschung, Forschungszentrum Jülich GmbH, Germany A R T I C L E INFO Keywords: DEMO Tokamak FEA Fusion Magnets ABSTRACT The equatorial plane of the inner leg of a toroidal feld (TF) coil is the most stressed part of the TF coil system and optimal usage of the radial space in this region is crucial for the design of the DEMO tokamak reactor. A pro- cedure for initial dimensioning (pre-dimensioning) of this region developed earlier [1] is based on a simplifed 2D geometry of the TF coil cross-section and a semi-analytical approach to estimate stresses in the TF coil case and the conductor jackets with limited capabilities for optimization. This work presents a new procedure named TFC-PREDIM which features a detailed 2D fnite element (FE) generalized plane strain model. The model gives very accurate results within a short calculation time and allows additional options for layout optimization. The FE model for the cross-section is generated automatically from the input geometrical parameters of the given layout allowing any of the conductor design options currently investigated for DEMO. The post-processing of the results is also automated, consisting in the determination of the maximum values of the membrane and mem- brane + bending Tresca stresses for each conductor jacket and for the TF coil case. Two strategies for the optimization of the cross-section are presented: minimization of the TF coil radial build with a predefned maximal toroidal feld and maximization of the maximal toroidal feld for a predefned radial space. 1. Introduction A TF coil represents a winding pack (WP), made of a set of wound conductors inserted into a massive coil case (Fig. 1). Each conductor consists of a superconducting cable enclosed in a steel jacket (conduit) and wound by insulating tape (Fig. 1). The jacket and the TF coil case serve as the structural support for the cable mainly against operational electromagnetic loads (EM). The radial extension occupied by the TF coil system at the equatorial plane of the inner leg defnes how much space is left for the central solenoid (CS) coil on one side and for the blanket system on the other. Therefore, it is important to use this space effectively and the design of a TF coils system always starts from the dimensioning of this particular cross-section. A zero order approximation for a DEMO radial build is provided by the PROCESS system code [2] which defnes the available radial space for the TF coil case and the winding pack (WP) at the inner leg, considering a simplifed stress model and operational EM loads. Before conducting further analyses an actual design of the WP has to be developed which includes the specifcation of the number of conductors, cross sectional dimensions of the cable, jacket and insulation. Sometimes this can be performed automatically by system codes like SYCOMORE [3] but their capabilities, especially for the mechanical optimization, are still limited to a set of simplifed analytical equations insuffcient for the detailed description of the geometry. The mechanical design of the WP consists in an estimation of the required wall thickness for the conductor jackets. To produce an initially mechanically pre-optimizedF WP layout a special “pre-dimensioning” procedure was developed [1]. The procedure relies on a simplifed 2D semi-analytical approach to determine membrane stresses in the toroidal and radial conductor jacket walls under operational EM loads. It has a capability of optimization of a WP layout by variation of the conductor jackets wall thickness to minimize the radial built while satisfying a structural strength criterion on the membrane stress. In this paper a new pre-dimensioning procedure TFC-PREDIM is described. It relies on the same principles for stress calculation as the previous one [1]: 2D cross section at the equatorial plane of the inner leg, generalized plane strain assumption and analytical approximation of the in-plane EM forces, but also has several advantages. It features a detailed fully parametrically defned 2D FE geometry of a coil * Corresponding author. E-mail address: i.ivashov@fz-juelich.de (I. Ivashov). Contents lists available at ScienceDirect Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes https://doi.org/10.1016/j.fusengdes.2020.111948 Received 11 March 2020; Received in revised form 30 June 2020; Accepted 5 August 2020