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Behaviour of a carbon wall under fusion reactor conditions

Submitted by devries on 28 October 2011 - 2:31pm

28 October 2011
In future fusion reactors, erosion and re-deposition of wall materials by the hot fusion plasma is a big concern. Scientists at FOM Rijnhuizen have studied in detail how erosion and re-deposition of carbon takes place. The Rijnhuizen plasma experiment Pilot-PSI is one of the few in the world which can create the never-before-seen intense plasma conditions expected at the exhaust or divertor of the advanced fusion reactor ITER.

 

Hydrogen plasma in the plasma surface interactions experiment Pilot-PSI

 

One of the materials planned for use in ITER is carbon. Erosion of that material by the hot, dense hydrogen plasma is a big concern for the lifetime of these components. An even bigger concern is the abilty of re-deposited carbon to absorb and retain lots of fuel, which is then unavailable for the fusion reaction. Together with international colleagues, Rijnhuizen PhD-student Kirill Bystrov determined how the erosion of carbon changes over time.

 

Cauliflower-shaped dust

The amount of removed carbon atoms over time turns out to be strongly connected to what is happening on the surface of samples. Scanning electron microscopy shows that eroded carbon is re-deposited on the surface in the form of microscopic cauliflower-shaped dust particles. These are barely attached to the bulk of the  material, which leads to overheating and decrease of erosion yield.The longer the carbon surface was exposed to plasma, the more and bigger cauliflower-shaped dust particles developed.

 

Scanning Electron Microscopy of a carbon surface before (a and b) and after exposure to a hydrogen plasma (c and d). The development of cauliflower-shaped dust particles is clearly visible.

 

To measure the amount of erosion, the team used the fact that carbon forms methane molecules with hydrogen. When in plasma, these emit visible light in a telltale wavelength near the blue-purple end of the spectrum and so can be detected relatively easy.

 

Cover article – Journal of Nuclear Materials

 

This research was published on the cover of the August 2011 issue of the Journal of Nuclear Materials by a cooperation between the FOM Institute for Plasma Physics Rijnhuizen, Forschungszentrum Jülich and Basel University.

 

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