Description
Tokamak operation with tungsten walls, as foreseen in ITER and future fusion-based power plants, faces the potential strong impact of tunsgten dust ingress in the plasma. This was documented on the WEST tokamak [Bucalossi2024], equipped with an ITER-grade tungsten divertor, during a high fluence campaign in attached divertor condition: the erosion of tungsten monoblocks generated deposits that could detach and trigger plasma disruptions [Gaspar2024]. The operation in a radiative divertor regime mitigates the risk of building tungsten deposits [Gaspar2026], but a deterioration of plasma operation could be seen after cumulating the equivalent of a single ITER pulse (Q=10, 400s) in attached divertor condition. Being able to predict the impact of such dusts in present tokamaks is therefore instrumental, although the task is on many aspects extremely complex [Smirnov2020]. The modelling of tungsten dust penetration in WEST is performed with the DUSTTRACK code [Gervasini2027], investigating the tungsten deposition dependence on the dust size and speed. It shows that for similar range of size and speed, the dust is penetrating further inside in WEST compared to JET [Lazzaro2022], due to the lower plasma temperature. The impact on the plasma evolution is then modelled with the High Fidelity Pulse Simulator (HFPS) based on JINTRAC [Romanelli2024], with different levels of complexity, from a prediction of current diffusion only, up to a prediction of particle (D, N and W) and heat transport using TGLF [Staebler2021]. With current diffusion only, resistive MHD mode triggering on q=2/1 is found for a dust mass above 20µg, consistent with experimental observations [Maget2024]. With the more complete simulation scheme, we find that the localization of the tungsten source inside the plasma boundary plays an essential role in the observed plasma evolution. The validation of this workflow on WEST is a first step towards the evaluation of the maximum allowed dust size in larger tokamaks and the associated mitigation strategies.
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