Exploring the role of topography in the sputtering process of tungsten by GyM helium plasma

This work investigates the role of surface topography in the sputtering process of tungsten (W) exposed to helium plasma using the GyM linear device. Surfaces with varying roughness, from sub-nanometer to approximately 1 µm, and different textures, including random-like and regular configurations, were studied. The samples were exposed to helium plasma of GyM at energies ranging from 30 to 350 eV, with a fluence of ≈ 4.3 × 10 24 He+m−2 and temperatures well below the bulk W fuzz formation threshold of ≈700 ∘C. The interpretation of the experimental results was supported by simulations with the 3D Monte Carlo ERO2.0 code. Analysis with atomic force and scanning electron microscopy revealed that surface topography remained largely unchanged, while a nanoscale undulating surface structure formed on all samples at the highest incident energies. The effective sputtering yield ( Y eff ) of tungsten, derived from mass and thickness loss data, was consistently lower than predictions from simulations by up to an order of magnitude, likely due to the dynamic retention of helium on the tungsten surface. On the other hand, both experimental results and modelling agree that surface topography’s influence on sputtering can be entirely captured by the average surface inclination angle ( δ m ), which unequivocally characterises each specimen, unlike the average roughness ( R a ). Moreover, Y eff values from both mass loss data and ERO2.0 simulations as a function of δ m align well with a decreasing sigmoid fit function. A reduction of more than 50% was observed when comparing the flat surface to that with the highest R a , attributed by ERO2.0 to the increasing fraction of sputtered tungsten atoms being deposited on neighbouring surfaces. These findings underscore the importance of accurately calibrating simulation tools against linear plasma device experiments for predicting the lifetime of plasma-facing components in fusion reactors such as ITER and DEMO, emphasising the potential of structured tungsten surfaces to reduce erosion and impurity concentration in the plasma core.