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Plasma Wall Interaction (PWI TCP)
Testing materials with linear plasma devices
The PWI TCP conducts research to understand the phenomena of interaction between the plasma and the chamber walls and to develop relevant wall materials for applications in fusion power. To reproduce the radiation levels expected with ITER, materials for plasma wall-facing components are being tested in linear plasma devices.
Materials that line the fusion chamber walls must withstand extreme temperatures of 100 million °C and be robust enough to maintain structural homogeneity when coming into contact or interaction with the plasma. The effect of the plasma on the wall components and the influence of eroded material on the plasma is an important focus of fusion research.
In ITER and DEMO the amount of heat and particles from the plasma is expected to be much larger than in any existing device. Fast neutrons released by the deuterium tritium reaction risk damaging chamber wall materials and degrading the plasma-facing components. The combined effects of heat, particles and neutrons will affect the lifetime of the wall components in a fusion reactor – and the cost-efficiency of the facility.
For these reasons the PWI has been focusing research on chamber wall materials in dedicated facilities such as linear plasma devices.** These facilities enable experiments in the field of plasma wall interactions similar to conditions expected with ITER and DEMO. The new devices are also capable of handling neutron irradiated materials that allow for a combination of different scenarios.
The PWI TCP experimental programme is closely linked with the development of novel, advanced materials capable of withstanding extreme conditions. Tungsten-based materials are the most promising for fusion reactors because of their high melting point (3 422°C) and efficient thermal conductivity.
Nevertheless the bombardment of tungsten surfaces with a high amount of particles erodes the surface, leading to microstructural changes in the material. Tungsten can also absorb hydrogen during plasma exposure, which increases the risk of the release of a significant amount of radioactive fusion fuel in the event of an accident.
The PWI TCP compared the impact of plasma exposure on surfaces and hydrogen retention in tungsten in steady-state and short-lived modes of plasma operation. Findings from recent experiments show that the absorption of hydrogen and the formation of defects in the tungsten components are strongly dependent on the magnetic force passing through the plasma and the surface temperature during exposure.
Further research is required to select and develop suitable first wall materials for future fusion reactors. Results of these experiments are detailed in the report, Influence of Particle Flux Density and Temperature on Surface Modifications of Tungsten and Deuterium Retention.
* Photo courtesy of Forschungszentrum Jülich GmbH
- Characterisation of plasma edge properties
- Development and qualification of first wall materials
- Development of diagnostics for edge plasma and material surface characterisation
- Modelling of plasma wall interaction studies
- Surface characteristics under intense particle and heat loads
For more information: www.fz-juelich.de/fusion
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