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Institute of Energy and Climate Research (IEK)

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High-Temperature Composite Materials

Plasma facing materials for thermonuclear fusion devices

Team 2017

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Controlled thermonuclear fusion is getting more and more attention as a long term energy source due to the inexhaustible fuel resources and its potential to generate energy without any significant CO2-emissions. With ITER, magnetic confinement fusion is now entering a new phase to demonstrate its technical and economic feasibility.

The nuclear fusion process is characterized by an extreme energy release in the range of several MeV per nucleon; hence, the energy density and thus the thermal fluxes to the plasma facing wall in fusion reactors are much higher compared with fossil fuel or other energy conversion technologies. This makes high demands on the materials; in particular high temperature resistant materials with a high thermal conductivity are required. From an engineering point of view, one of the most challenging issues is the development of fatigue resistant plasma facing component, being compatible with plasma induced quasi-stationary heat fluxes up to approximately 20 MW/m² and short transients in the GW/m² range. In addition, all in-vessel components have to withstand high neutron doses without unacceptable activation and deterioration of the materials.

A major aim of our research activities is to develop new materials, coatings and joints, and to characterize them with respect to their thermal and mechanical properties in a wide temperature range. Furthermore the performance and degradation of plasma facing materials and components under fusion relevant heat/particle loads and neutron fluxes is another important R&D subject.

With respect to the aforementioned constraints, the following materials are of particular interest because of their excellent characteristics: refractory metals (especially tungsten (W)), low-activation steels (SS), beryllium (Be), graphite or carbon fibre composites, fibre reinforced materials and coating systems. Significant applications for these materials besides the use as plasma facing or structural material in fusion reactors are minor gas turbines, collectors for focused solarthermics, contact materials for high electrical power applications or high performance electronics (component concepts), high performance X-ray tubes, fireproof materials, and extreme ultra violet lithography.

The current research activities/emphases are divided in three major topics. Within the topic of material and component characterisation, thermophysical and mechanical material properties are determined. Additionally, the influence of these properties on the thermomechanical fatigue and thermal shock performance are evaluated. Furthermore, the influence of hydrogen, helium, and neutron irradiation on the material parameters is studied. High-temperature materials (W, SS, Be etc.) are subjected to fusion relevant thermal loads and qualified. Thereby, synergistic effects between the pure thermal loads and the particle loads (H, He, n) play a major role. Furthermore, high-temperature materials and components are deliberately pre-damaged for subsequent experiments.

A further topic in the material and method development is the in-situ repair of damaged high-temperature materials and the minimisation of critical stress states in thermally loaded materials/components via e.g. functionally graded materials (FGMs). The experimental data and conclusions of the two prior topics build up the basis for the third topic, numerical simulations. Finite element method (FEM) simulations are utilized to calculate thermomechanical processes in materials and components under transient and stationary thermal loads. These simulations allow predictions of the thermomechanical fatigue behaviour and lifetime of the materials and components under thermal and particle loading. The combination of experimental studies and numerical calculations leads to a better understanding of failure mechanisms, enables the optimisation and development of existing high-temperature materials and components, and serves as starting point for the development of new material concepts. The fusion related activities are performed with the long term goal to develop the technologies necessary for a demonstrational power plant (DEMO) in mind.

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Modell des Europäischen Demonstrationskraftwerkes (DEMO)Modell des Europäischen Demonstrationskraftwerkes (DEMO)

Additional Information

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ITER schemeITER scheme

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Tungsten meltTungsten melt droplet after transient thermal loading

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Beryllium filamentsBeryllium filaments solidified during the thermal contraction phase