The provision of a particle and power exhaust solution which is compatible with first-wall components and edge-plasma conditions is a key area of present-day fusion research and mandatory for a successful operation of ITER and DEMO. The work package plasma-facing components (WP PFC) within the European fusion programme complements with laboratory experiments, i.e. in linear plasma devices, electron and ion beam loading facilities, the studies performed in toroidally confined magnetic devices, such as JET, ASDEX Upgrade, WEST etc. The connection of both groups is done via common physics and engineering studies, including the qualification and specification of plasma-facing components, and by modelling codes that simulate edge-plasma conditions and the plasma-material interaction as well as the study of fundamental processes. WP PFC addresses these critical points in order to ensure reliable and efficient use of conventional, solid PFCs in ITER (Be and W) and DEMO (W and steel)

The sputtering of wollastonite (CaSiO3) by solar wind-relevant ions has been investigated experimentally and the results are compared to the binary collision approximation (BCA) codes SDTrimSP and SRIM-2013. Absolute sputtering yields are presented for Ar projectiles as a function of ion impact energy, charge state and impact angle as well as for solar wind H projectiles as a function of impact angle. Erosion of wollastonite by singly charged Ar ions is dominated by kinetic sputtering. The absolute magnitude of the sputtering yield and its dependence on the projectile impact angle can be well described by SDTrimSP as long as the actual sample composition is used in the simulation. SRIM-2013 largely overestimates the yield especially at glancing impact angles. For higher Ar charge states, the measured yield is strongly enhanced due to potential sputtering. Sputtering yields under solar wind-relevant H + bombardment are smaller by two orders of magnitude compared to Ar. Our experimental yields also show a less pronounced angular dependence than predicted by both BCA programs, probably due to H implantation in the sample. Based on our experimental findings and extrapolations to other solar wind ions by using SDTrimSP we present a model for the complete solar wind sputtering of a flat wollastonite surface as a function of projectile ion impact angle, which predicts a sputtering yield of 1.29 atomic mass units per solar wind ion for normal impact. We find that mostly He and some heavier ions increase the sputtering yield by more than a factor of two as compared to H + bombardment only.

The influence of surface morphology modifications on the sputtering yield of thin Fe films by monoenergetic Ar ions is studied by using a highly sensitive quartz crystal microbalance (QCM) technique. The morphology changes are induced by prolonged sputtering up to a total Ar fluence of 8 x 10 21 m-2. Atomic force microscopy (AFM) measurements are performed to analyse the sample topography before and after irradiation and to determine surface roughness parameters. Numerical modelling with the codes SDTrimSP and SDTrimSP-2D are performed for comparison. Our investigations show that by using the local distribution of projectile impact angles, as derived from AFM measurements, as well as the elemental composition of the samples as an input to the codes SDTrimSP and SDTrimSP-2D the agreement between experiment and simulations is substantially improved.

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Transient effects during erosion of polycrystalline tungsten-nitride (WN) films by mono-energetic deuterium projectiles are studied using a quartz crystal microbalance technique. The evolution of the mass removal rate of a 360 nm thin WN film under 500 eV/D and 1000 eV/D bombardment is investigated at a temperature of 465 K in situ and in real-time as a function of the deuterium fluence. The measurements are performed at a typical flux of 10 18 m-2 s-1. A strong dependency of the observed mass change rate on the deuterium fluence is found. The mass loss is initially higher than for pure tungsten (W) and drops with fluence, finally reaching the same steady state value as for pure W sputtering. Steady state surface conditions are obtained at a fluence of about 0.2×10 23 D/m² for 500 eV/D and 0.6×10 23 D/m² for 1000 eV/D. SDTrimSP simulations indicate a preferential removal of N and a corresponding W enrichment of the surface.