Erosion investigations in GLADIS

The specific loads of components exposed to plasma impact are being simulated in the test facility GLADIS under well-defined conditions.

View into the divertor of ASDEX Upgrade, which is equipped with tungsten target plates.

In fusion reactors tungsten will presumably be employed as protective material for plasma-facing components. Specifically, the divertor components are exposed to the strong impact of plasma particles – hydrogen and in a power plant also the fusion product helium – and correspondingly to a high thermal load. Such loads of heat and particles can be generated in IPP’s facility GLADIS (Garching Large Divertor Sample Test Facility).

Tungsten components can be exposed to particle and heat fluxes of up to 40 megawatts per square metre. Admixture of a few per cent helium to the hydrogen already causes the formation of complex structures on the surfaces of the components, which can influence their wear behaviour and therefore their lifetime. The investigations comprise specifically the near-surface morphology, the erosion behaviour, and the amount of hydrogen and helium atoms retained in the material.

Electron-microscopic image of a tungsten surface originally polished smooth after testing in GLADIS. In the tests the surface temperature ranged up to 2000 °C. The scale bar at the bottom right is one micrometre.

Various tungsten materials and alloys are being investigated with GLADIS. This also involves parts produced by powder injection moulding, which is a research topic at KIT in Karlsruhe.

The inventory of hydrogen retained in the material after loading can be determined in IPP’s tandem accelerator laboratory. Since the temperature-dependent outgassing of hydrogen can be well described by computer models developed at IPP, the experimental results can be integrated into predictions of the hydrogen isotope balance of future power plants. One of the objectives is modelling of structural changes and erosion to obtain a better estimate of divertor component lifetimes.

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