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Description
Understanding plasma–wall interaction is a key step on the path towards the exploitation of nuclear fusion energy [1]. The erosion of plasma-facing components (PFCs) can shorten their lifetime, while the eroded material — typically tungsten (W), owing to its favourable plasma-interaction properties — may contaminate the confined plasma, degrading the performance through fuel dilution and increased radiative losses. Part of this material can also re-deposit on the wall, promoting co-deposition of fuel species, including radioactive tritium. In fusion plasmas, these processes may be further amplified by heavier and multiply ionized impurities, such as helium (He) produced by D–T reactions, which can enhance sputtering.
Since a tokamak, the most common reactor design, is an intrinsically complex system, experiments alone often do not allow to disentangle the contribution of the different mechanisms involved. Numerical modelling therefore provides an essential complement, improving the interpretation of measurements and enabling extrapolations to future devices.
This work focuses on the analysis of a He-plasma campaign on the ASDEX Upgrade (AUG) tokamak [2] using an integrated approach that couples SOLPS-ITER, a 2D multi-fluid edge plasma code [3], and ERO2.0, a 3D Monte Carlo code for erosion and impurity transport [4]. Two reference discharges are considered, representative of low and high confinement regimes (L- and H-mode). SOLPS-ITER is used to reconstruct edge plasma conditions and the relative fractions of the two possible He charge states, supplying the background plasma to ERO2.0, which in turn simulates tungsten erosion from the outer divertor target and subsequent impurity transport.
Net erosion profiles are estimated along the outer divertor, showing that He²⁺ is the dominant sputtering contributor and that the steady state phase in H-mode exhibits peak erosion several times higher than L-mode. A parametric scan on plasma temperatures and on the presence of additional impurities — using oxygen (O) as a proxy — indicates that uncertainty on these factors can noticeably reshape the erosion profile. Comparison with available divertor erosion measurements [5] confirms the need to include foreign impurities in the description for L-mode, and the predominance of erosion driven by transient edge localized modes (ELMs) in H-mode.
[1] Roth J. et al, J. Nucl. Mater. (2009) 390–391 1–9
[2] Hakola A. et al, Nuclear Fusion 64.9 (2024) 096022
[3] Bonnin X. et al, Plasma Fusion Res. 11 (2016) 1403102
[4] Romazanov J. et al, Phys. Scr. T170 (2017) 014018
[5] M. Rasiński et al. NME 37 (2023) 101539
Acknowledgements: Part of this work is funded by Eni S.p.A, in the framework of the contract N. 4400010490. This work has been carried out within the framework of the EUROfusion Consortium (WP-PWIE), partially funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200—EUROfusion)
