The change of surface topography of plasma facing components in controlled fusion devices

Surface microstructure and composition of plasma facing components from the TEXTOR tokamak are described. Surfaces of such components are drastically modified by the impact of plasma ions. This interaction results in the formation of thick co-deposited/co-implanted layers containing a mixture of hydrogen isotopes and plasma impurity species. The emphasis is on the characterisation of changes occurring on the graphite surface exposed for a few hours to a hot deuterium plasma and, afterwards, following the exposure either to air or annealing in vacuum at elevated temperatures. The investigation carried out by means of electron microscopy, energy dispersive X-ray spectroscopy, ion beam analysis methods and laser profilometry gives evidence on the conditions under which the deuterium is released due to the oxidation or desorption from the plasma eroded surfaces. It is also demonstrated that the oxygen-assisted removal of deuterium at 300°C has rather small impact on the decomposition of thick co-deposits.