Finite element based design optimization of WENDELSTEIN 7-X divertor components under high heat flux loading

Abstract

In the divertor of the nuclear fusion experiment WENDELSTEIN 7-X (W7-X) plasma facing high heat flux target elements have to withstand severe loading conditions. The thermally induced mechanical stressing turns out to be most critical with respect to lifetime predictions of the target elements. Therefore, different design variants of those CFC flat tile armoured high heat flux components have been analysed via the finite element package ABAQUS aiming at derivation of an optimized component design under high heat flux conditions. The investigated design variants comprise also promising alterations in the cooling channel design and castellation of the CFC flat tiles which, however, from a system integration and manufacturing standpoint of view, respectively, are evaluated to be critical. Therefore, the numerical study as presented here mainly comprises a reference variant that is comparatively studied with a variant incorporating a bi-layer-type AMC-Cu/OF-Cu interlayer at the CFC/Cuinterface.The thermo-mechanical material characteristics are accounted for in the finite element models with elastic-plastic properties being assigned to the metallic sections CuCrZr, AMC-Cu and OF-Cu, respectively, and orthotropic nonlinear-elastic properties being used for the CFC sections. The calculated temporal and spatial evolution of temperatures, stresses, and strains for the individual design variants are evaluated with special attention being paid to stress measures, plastic strains, and damage parameters indicating the risk of failure of CFC and the CFC/Cu-interface, respectively. This way the finite element analysis allows to numerically derive an optimized design variant within the framework of expected operating conditions in W7-X.

Review of the high heat flux testing as an integrated part of W7-X divertor development

“…This 2mm thick soft Cu layer acts as compliant interlayer and reduces the stress level at the CFC/Cu interface to about 50% [4,5]. A modification of the welding design of the cooling structure by introducing of a central fin increased the stiffness and ensures constant cooling conditions during operation.…”

Cyclic heat load testing of improved CFC/Cu bonding for the W 7-X divertor targets

“…No large detachment or loss of CFC tiles occurred during previous cyclic loading tests performed in the neutral beam facility GLADIS [9], but growing local degradation of bonding at the free edges of several CFC tiles was observed. Therefore a detailed nonlinear thermo-mechanical FEM analysis of the CFC/Cubonding system was carried out with a view to achieving a reduction of the stress at this interface [10]. Based on the results of the analysis, 17 additional pre-series elements with different bonding options were manufactured (Fig.…”

Mechanical and thermo-physical characterization of three-directional carbon fiber composites for W-7X and ITER

“…These have to fulfill the occurring manufacturing and operational needs which is nowadays also a matter of numerical simulations [5,10]. Among these materials are several CFCs, for which the characterization results are summarized in [11,12].…”