Plasma-surface interactions in controlled fusion devices comprise a broad set of processes responsible for the change of structure and chemical and thermo-mechanical properties of plasma-facing components (PFC). Their surface is irradiated by particle fluxes escaping the edge of hot hydrogen isotope plasmas. Physical sputtering, chemical erosion and other processes cause removal of surface atoms mainly from the so-called erosion zones. Species eroded from the wall enter the plasma as impurities. They are instantly ionised, move along the magnetic field lines and, afterwards, become re-deposited in another location (so-called deposition zones) than the place of origin. The latter process is accompanied by co-deposition of hydrogen isotopes. Plasma is usually in contact with components made of more than one single element. As a consequence of erosion and re-deposition new mixed materials with diverse hydrogen content are formed.
The aim of this paper to present an overview of changes in the surface structure and composition of PFM. The study was carried out with different materials (e.g. graphite and tungsten) exposed to the plasma in the TEXTOR tokamak, a controlled fusion device in Forschungszentrum Jülich. The exposure time varied from a few seconds for short-term probes to several hours of plasma operation in the case of major PFC (toroidal limiter and inner wall tiles). Following the exposure, analyses of materials retrieved from the vessel were performed using accelerator-based ion beam analysis methods including nuclear reaction analysis, Rutherford backscattering spectroscopy, enhanced proton scattering, high-resolution microscopy, energy and wavelength dispersive X-ray spectroscopy and other techniques. This allowed for the determination of: (i) the layer thickness, composition and structure; (ii) the layer growth rate in deposition zone under various conditions, (iii) content and depth profiles of hydrogen isotope in the layers.
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