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Description
The physical sputtering rate of tungsten (W) and its sensitivity to scrape-off-layer (SOL) fluctuations is characterised as the first application of time-dependent ERO2.0 [1] full-orbit Monte Carlo simulations in fluctuating turbulent plasma conditions. A time-dependent 3D description of global edge-SOL turbulence is obtained from validated GRILLIX [2] simulations. The studied plasma scenario is a diverted attached L-mode plasma in the ASDEX Upgrade tokamak. The time evolution of the plasma profiles is extracted from GRILLIX into ERO2.0 with a resolution of 5 µs in time and ~1 mm in space. The simulated W sources are validated by comparing W I 400.9 nm line emission spectrometer measurements with synthetic W I diagnostics at the low-field side divertor target.
The GRILLIX plasma solution has density fluctuation amplitudes up to 150%, and ion temperature fluctuation amplitudes up to 250% of the mean-field in the low-field side SOL [2]. Plasma filaments propagating radially outwards from the separatrix cause intermittent erosion of the W first wall in the main chamber. ERO2.0 simulations predict that the W net erosion rate in the far-SOL varies in time by more than an order of magnitude, mainly due to the intermittent impurity ion (B, O, W) fluxes.
In contrast to the strong fluctuations in the low-field side far-SOL, cross-field transport is low near the high-field side mid-plane and at the near-SOL outer divertor target in the studied conditions. A time-averaged mean-field approach enabling the use of a steady-state plasma solution is therefore a fair approximation at the outer strike line, but causes an underestimation of the W erosion sources in the far-SOL divertor and main chamber. While the highest W gross and net erosion source in the ERO2.0 simulations is located near the strike line, the W sources in the main chamber are less efficiently screened and contribute more to the predicted W density in the confined region.
[1] J. Romazanov et al., Nucl. Mater. Energy 18 (2019) 331-8
[2] W. Zholobenko et al., Nucl. Mater. Energy 34 (2023) 101351