Description
Following the ITER re-baseline to a tungsten First Wall (FW), accurate modelling of heavy impurity contamination during the plasma ramp-up phase is critical [1]. While boronisation is expected to restore oxygen gettering properties of the wall, the lifetime of the boron layer is under investigation [2]. This work presents the validation of the SolEdge-HDG code against long-duration limited plasma discharges in WEST to address these modelling needs.
Recent experiments on W machines [3] have highlighted the importance of numerical modeling in understanding plasma–wall interactions. SolEdge-HDG predicts high Te at the ITER first wall [4], while SOLPS-ITER shows a tungsten sputtering self-regulation mechanism but is limited to steady-state conditions [5]. In contrast, 1D models capture ramp-up transients [6] but rely on simplified boundaries. SolEdge-HDG overcomes these limitations with a self-consistent core–edge coupling, high-order spatial discretization, and efficient time-stepping, enabling full 2D dynamical simulations of discharges [4].
This work validates SolEdge-HDG against long limited discharges on WEST, highlighting key physics insights. Using constant transport reproduces midplane density profiles but underestimates core electron temperature and produces overly steep SOL gradients. Introducing physics-based transport models [7,8] mitigates these discrepancies without ad-hoc tuning. Initial limiter profiles are more peaked than Langmuir probe measurements; implementing improved Bohm boundary conditions at shallow incidence angles brings simulations into closer agreement. Broader plasma profiles also enable boron sputtering far from the midplane, emphasizing the role of far-SOL dynamics. Finally, the impurity radiation model reproduces bolometer signals and enhances limiter Te predictions. Coupling to ERO2.0 [9] reveals how spatially resolved plasma–impurity interactions affect energy losses, showing that achieving power balance alone is insufficient for accurate Te modeling. Finally, it reproduces the observed with visible spectroscopy up–down radiation asymmetry, attributed to small magnetic equilibrium asymmetries.
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[9] Romazanov, J., et al. CPP 60.5-6 (2020): e201900149.