N. Jaksic

A solid tungsten divertor for ASDEX Upgrade

The conceptual design of a solid tungsten divertor for ASDEX Upgrade (AUG) is presented. The Div-III design is compatible with the existing divertor structure. It re-establishes the energy and heat receiving capability of a graphite divertor and overcomes the limitations of tungsten coatings. In addition, a solid tungsten divertor allows us to investigate erosion and bulk deuterium retention as well as test castellation and target tilting. The design criteria as well as calculations of forces due to halo and eddy currents are presented. The thermal properties of the proposed sandwich structure are calculated with finite element method models. After extensive testing of a target tile in the high heat flux test facility GLADIS, two solid tungsten tiles were installed in AUG for in-situ testing.

Main Results and Critical Issues of W7-X Structural Analysis

The goal of the Wendelstein 7-X (W7-X) stellarator project is to demonstrate that this type of machine is a viable option for a fusion power-plant. At present the W7-X experiment is in the assembly phase at the Max-Planck-Institut for plasma physics in Greifswald, Germany. The reliable prediction of the structural behavior of the W7-X machine is only possible by employing complex finite element (FE) analyses with a hierarchical set of FE models. A special strategy has been developed for the structural analysis which is under implementation now. This paper gives an overview of the analysis strategy, the applied structural criteria and critical issues, and focuses on the most remarkable results. The main attention is paid to the components that have been changed or optimized recently.

On Mechanical Boundary Conditions in Large Helias Coil Systems and the Influence of Sliding on Stresses

The WENDELSTEIN 7-X stellarator experiment is developed as a Helias (Heli cal A dvanced S tellarator) configuration. The superconducting modular coils with nonplanar shape introduce a magnetic field with a maximum net coil force of about 4 MN. The resultant force vector of a whole field period is directed towards the torus centre. In order to support the magnetic forces, a scheme of mutual support has been developed. Each coil is enclosed by an individually adapted stainless steel housing. The coils of a field period are connected to a module by a pair of reinforcements inside the torus. For reasons of accuracy calculations are made within one period. The investigated stress levels in the coils and support depend on the mechanical contact between winding pack and coil housing. The nonplanar coils lead to difficulty in defining the bearing conditions at the ends of a period. The assumptions for prescribing these boundary conditions, which are needed for the FE analysis, are presented.

Final structural and mechanical evaluation of the W7-X magnet support system

The plasma fusion experiment WENDELSTEIN7-X (W7-X) of the stellarator family, which was developed at the Max-Planck-Institute for Plasmaphysik, is in the state of the final detail design. W7-X is planned for first operation in 2006. Currently the main components (coils, magnet support structure, vacuum vessel, …) are ordered to be manufactured. This paper gives a summarization of the development of the magnet support structure during the last 10 years. Of course, the final design and its structural analyses are the main topic of the discussion. Finally, it is tried to summarize the cognitions won until now and based on this knowledge to give the recommendations for future activities.

Buckling Analysis and Results Post-Processing of the W7-X Inner Vacuum Vessel

Abstract The magnet of the WENDELSTEIN 7-X stellarator consists of five modules each containing five types of non-planar coils as presented in Ref. [1]. Two vessel systems outside and inside the toroidal magnet curvature confine the vacuum for cryogenic operation. The shape of the inner vacuum vessel is defined by the geometry between the surface of the plasma and the inside surface of the coils. The subject of this analysis is the test cryostat for W7-X. A buckling analysis has been performed to obtain the critical-load factors. The method used to perform the calculations is described together with some special demands for the post-processing.

Transient Thermal and Structural Mechanics Investigation of the New Solid Tungsten Divertor Tile for Special Purposes at ASDEX Upgrade

A new solid tungsten divertor for the fusion experiment axial symmetric divertor experiment upgrade is under construction at present. For special purposes of the plasma diagnostic in the divertor region, special formed solid tungsten divertor tiles are required. A so-called Langmuir probe is used to determine the ion temperature, ion density, and ion potential of the plasma. With the aim to place the probe on the right position, some of the divertor tiles (nine at the device circumference) have been adequately adapted. This paper discusses the main results of the numerical analysis of the thermomechanical behavior under heat load. Initially, the elastic-plastic calculation was applied to analyze thermal stress and the observed elastic and plastic deformation during the heat loading. The influence of a possible material degradation due to thermal cracking was studied. Additionally, the knowledge gained by the numerical analysis was used for the shape optimization of the divertor tile. The first results from the numerical life cycle analysis of the tungsten tiles are reported. Finally, based on the knowledge gained by the numerical analysis, in the light of problem complexity, it is recommended to perform some additional thermal tests. These tests should be performed with the aim to increase the reliability of the special-shaped tungsten tile during operation.

Thermo-mechanical investigation of the new solid tungsten divertor tile for special purposes at ASDEX upgrade

A new solid tungsten divertor for the fusion experiment ASDEX (Axial Symmetric Divertor EXperiment) Upgrade is under construction at present. For special purposes of the plasma diagnostic in the divertor region a special formed solid tungsten divertor tile is required. A so-called Langmuir probe is used to determine the ion temperature, ion density and ion potential of the plasma. With the aim to place the probe on the right position some of the divertor tiles (9 at the device circumference) have been adequately adapted. This paper discusses the main results of the numerical analysis of the thermo-mechanical behavior under heat load. Primary, the elastic-plastic calculation was applied to analyze thermal stress and the observed elastic and plastic deformation during the heat loading. The influence of a possible material degradation due to thermal cracking was studied. Additionally, the knowledge gained by the numerical analysis was used for the shape optimization of the divertor tile. The first results from the numerical life cycle analysis of the tungsten tiles are reported. Finally, based on the knowledge gained by the numerical analysis, in the light of problem complexity, it is recommended to perform some additional thermal tests. These tests should be performed with the aim to increase the reliability of the special shaped tungsten tile during operation.