G. Czymek

Approaches to numerical modeling in development process of complex structures for fusion devices

Development of components for fusion device normally comprises numerous simulations to validate their design compatibility with the specified loads according to applicable codes and standards. A strategy of multifield finite element analyses is determined by an iterative nature of design process, and a level of a structure complexity dictates analysis approaches and modeling technique. Nowadays powerful software exploiting the strength of modern computers allows simulating structures in a very detailed way, even for some types of coupled field analyses. As some drawback of this tendency, many efficient numerical tools, used in the past, are not frequently engaged. Sometimes huge numerical resources are spent to solve trivial problems. Direct CAD-analysis meshing of structures in all their complexity may mix effects of different importance and may lead to overlooking some key structure features. Computational problems with convergence in nonlinear analyses often make modeling less flexible to design changes. This paper gives examples of engineering simplified modeling made with clear understanding of an analysis goal and a role of simulations in design process, like for the W7-X stellarator busbar system. Engineering methods to perform multifield analysis including electromagnetic transients for some ITER diagnostics are also presented. An engineering material model to calculate steel superconducting structures working in inelastic range is discussed.

110 GHz notch-filter development at TEXTOR-94

Abstract After the installation of a 110 GHz gyrotron at TEXTOR-94 the development of 110 GHz notch-filter was necessary for protecting the sensitive Electron Cyclotron Emission (ECE)-diagnostic, covering the frequency range 104≤ f ≤148 GHz. The design and construction of a narrow (Δ f ≤1000 MHz) and deep ( A max ≥50 dB) notch filter is explained. Furthermore the behaviour at different modes is studied. Also the influence of the aperture on the width of the notch as well as the influence of the number of used cavities on the depth of the notch and the losses in the pass band is studied and presented in the paper.

Strategies of Numerical Modeling in Component Development for Fusion Devices

The development of components for fusion devices includes numerous simulations to validate their design compatibility with specified loads according to applicable codes and standards. The strategy of multifield finite element analyses is determined by the iterative nature of the design process. The level of structural complexity dictates the analytical approaches and modeling techniques. Even though nowadays powerful software exploiting the performance of modern computers allows structures to be simulated in a very detailed way, direct meshing of CAD models with all their complexity is often not beneficial for nonlinear and multifield analyses. Reasonable modeling simplifications, submodeling, and integration with analytical modeling and testing can optimize the analysis process. This paper gives examples of simplified modeling for engineering purposes with a clear understanding of the analysis goal and the role of simulations in the design process, such as for the W7-X stellarator busbar system. Engineering methods to perform multifield analyses including electromagnetic transients for ITER diagnostic port plug components are also presented. An engineering material model is discussed for calculating the superconducting coil steel structures operating in the inelastic range.

Sensitivity Study of Mechanical Behavior of Busbar System Designed for Wendelstein 7-X Stellarator

The Wendelstein 7-X stellarator is now under construction in Greifswald, Germany. The superconducting busbar system for the stellarator coils is designed and manufactured at the Forschungszentrum Jiilich, Germany. The electromagnetic forces on the long busbars, considerable relative tilting of the coils carrying the busbar supports, lack of available space required for the robust design of these supports, collisions with other systems during operation as well as the cooling down process had to be taken into account during design phase. Having a complex layout and complying with different, often contradictory requirements, the busbar system turned out to be sensitive to the manufacture and assembly tolerances. The modular structure of the magnet system implied the modular sequence of the busbar system production. The mechanical behavior of the busbar system has been numerically simulated for the module 5. The developed global model reflects main important features of the complex system in a relatively simple way. It proved to be useful tool for frequent iterations during design period and for numerous tolerance studies. The paper describes the main features of the numerical model and some results of the sensitivity study of the busbar system.

Eddy currents calculation in the TEXTOR 94 modified liner/vacuum vessel system during plasma disruption

Abstract The Dynamic Ergodic Divertor—to be installed inside the vacuum vessel of the TEXTOR 94 tokamak—requires a new liner design. The new liner represents a thin toroidal shell with numerous holes. One-third of the liner shell, facing the ergodic coils, is cut out for purposes of the ergodic divertor structures. To sustain the electromagnetic loads the cut-off edges of the inconel liner shell are reinforced with massive steel structures. Edges of the liner holes are reinforced with different types of steel structures. Calculation of the induced currents in the liner and vacuum vessel and electromagnetic forces on the structures due to interaction of the induced currents with the electromagnetic field during a plasma disruption is presented. The eddy currents in the segments of the vacuum vessel separated by bellows form closed loops. Because of numerous ports in the vacuum vessel and numerous holes in the liner, there are currents flowing perpendicular to the toroidal magnetic field. This leads to bending and twisting of the structures. The calculated electromagnetic forces were used for the subsequent structural analysis.

The Superconducting Bus-Bar System for Wendelstein 7-X - A Challenge to Engineering

Forschungszentrum Julich is contributing to the Wendelstein 7-X project among others with the superconducting bus-bar system. The scope is the design, qualification, manufacturing, and assembly of the superconducting bus bars and its appropriate supports. An overall concept of the bus-bar manufacturing was developed with the goal to optimize the process, to simplify the system assembly, and to provide easy transportation. A suitable insulation set up fulfilling all specifications was developed. For the qualification of the insulation and the fabrication process different samples have been fabricated and tested. The bus-bar support system has to take considerable loads due to cool down shrinkage, electromagnetic forces, and displacements imposed by the magnet system. General considerations led to the choice of a system of standardized components which allows assembly of specific adjustable supports for each position. The complexity of the system geometry and its loading required an iterative approach of support design and stress analysis. Finally, an assembly sequence for the bus-bar system was found matching the technological requirements of the bus itself with all geometric and other constraints of the assembly facility.

Elastic-plastic cyclic deformation of the TEXTOR 94 modified liner under conditions of heating and plasma disruption

Abstract The present liner of the TEXTOR 94 tokamak installed inside the vacuum vessel represents the thin toroidal shell that is rested on the vessel inner surface. In order to integrate the dynamic ergodic divertor into the tokamak the liner design has been drastically changed. The 120° sector of the liner shell facing the ergodic coils system is removed and some additional holes in the liner are provisioned. This demands a new liner supporting system allowing for the liner thermal expansion and taking the electromagnetic load occurring in the liner during plasma disruption. The cyclic elasto-plastic deformations of the liner caused by the electromagnetic forces and temperature rise have been studied. It is shown that the local plastic deformations occur in the liner elements after the first heating and electromagnetic loading. The most thermal stresses take place in the reinforcing structures around the holes because of the thermal expansion difference of the inconel shell and the steel reinforcements. These stresses are coupled with the bending stress due to the electromagnetic loading. Subsequent repetitive loading does not lead to any significant increment of the plastic deformation. After the materials’ hardening the structure cyclically works mostly in the elastic range.