Speaker
Description
Understanding helium-induced plasma-surface interaction (PSI) on tungsten is essential for quantifying divertor erosion and impurity sourcing in magnetic confinement fusion devices, as He will inherently accumulate as a fusion ash. Experiments at ASDEX Upgrade have provided erosion, deposition and morphology data for He-based L- and H-mode discharges [1,2]. Here we present a modelling study to support the experimental campaign by providing physical insights into the H-mode PSI results, extending earlier L-mode analysis [3] and examining the role of edge-localised modes (ELMs).
The edge plasma was modelled with the state-of-the-art SOLPS-ITER mean-field boundary plasma code [4,5], while PSI and impurity transport were simulated with ERO2.0 [6], a 3D Monte-Carlo code. Optimised SOLPS-ITER simulations showed that both He$^{+}$ and He$^{2+}$ charge states contribute to divertor particle fluxes and that the inclusion of radiating impurities in the divertor region is required to reproduce experimental data. Additional simulations included hydrogenic species to account for H-based neutral beam injection heating. Overall, these simulations provided divertor plasma profiles, particle flux composition at the outer strike point (OSP) and optimised plasma background conditions for subsequent PSI and impurity transport modelling.
ERO2.0 simulations were performed for both inter- and intra-ELM phases. Inter-ELM modelling shows that a simplified He$^{2+}$-only plasma retains most of relevant PSI information, while the inclusion of impurity species strongly modifies the erosion pattern. O$^{6+}$ was chosen as a representative proxy for light impurities (B, C, N, and O) typically present in ASDEX Upgrade, capturing both impurity-driven sputtering and W self-sputtering amplification and allowing individual erosion contributions to be quantified. For the intra-ELM phase, a new approach was adapted from literature data [7,8], accounting for 1 keV He$^{2+}$ energy deposition at an 85° incidence angle at the OSP and an ELM frequency of 200 Hz - as experimentally recorded. This enabled ERO2.0 to reproduce the experimentally observed net erosion near the OSP – 120 nm over the 150-250 nm experimental range – and of net deposition in the near private flux region.
[1] A.Hakola et al. Nuclear Fusion, 64 (2024)
[2] M.Rasiński et al. Nuclear Materials and Energy, 37 (2023)
[3] G.Alberti, et al. arXiv preprint arXiv:2506.03883 (2025)
[4] S.Wiesen et al. Journal of Nuclear Materials, 463 (2015)
[5] X.Bonnin et al. Plasma Fusion Research, 11 (2016)
[6] J.Romazanov, et al. Physica scripta 2017.T170, (2017)
[7] A.Kirschner et al. Nuclear Materials and Energy 18, (2019)
[8] H.A.Kumpulainen et al. Nuclear Materials and Energy 33, (2022)