Mechanical examination and analysis of W7-X divertor module sub-structures

Abstract

For the long pulse operation phase, the W7-X stellarator is equipped with an actively water cooled high heat flux (HHF) divertor, consisting of parallel cooled target elements mounted in individual target modules. Due to the thermal deformation of these target elements during heat loading, the pipework that connects the target elements to the water supply manifold is subject to significant forces. Finite element calculations, for target modules TMh1-TMh2, show the superimposed forces of the whole pipework structure on to the manifold resulting in a torsional torque on the manifold support structure and weld. During manufacture, welding of the manifold to its support structure produces thermal induced distortion, resulting in difficulty in maintaining the accuracy of the manifolds. The welding between manifold and support structure was thus minimised in order to reduce this distortion. Finite element calculations showed that the nominal welds were acceptable; however, mechanical stress test on the manifolds mount point was carried out to prove the weld performance under the calculated loading conditions to ensure the safety of the component. For the remaining modules under design TMh1-TMh4 a parametric finite element calculation design study on the effect of the pipe length and routing on the stiffness helped to define minimum requirements for the design. The status of the manifolds for these modules will be shown. The manifolds are also mechanically connected to the port plug-in, therefore the impact of the thermal displacements on this pipework coming from plasma radiation affecting the target elements and from power loads coming from ECRH stray field radiation have been calculated. The paper discusses the results of the calculations and presents the outcomes of the stress test.

Assessment of the W7-X high heat flux divertor with thermo-mechanical analysis

“…Each module is a set of target elements (TEs) armored with CFC tiles mounted onto a stainless steel (SS) structure and fed in parallel with manifolds. A series of work including both HHF tests [5][6][7] and finite element simulations [8][9][10] has been performed to check the thermo-mechanical behavior of different parts of the divertor modules.…”

“…Previous detailed thermo-mechanical analysis has been performed on the TM9H module to support and complement the testing of the full-scale prototype of the same type [7,9]. This work identified critical areas such as the weld of water manifold holders and the transition between the water connectors of the TEs and the cooling pipes [10]. Based on the results of this analysis, the design of the TMs has been improved on well identified points and implemented in the production drawings.…”