Speaker
Description
Accurate numerical modelling of turbulent transport in edge tokamak plasma remains a significant challenge. Many key experimental features, such as the formation of edge transport barriers, are still difficult to simulate, especially for ITER-sized tokamaks. Predicting the scrape-off layer (SOL) width or the power load imbalance between the inner and outer divertor legs remain an open issue, their characterization being essential to determine the plasma regimes to be developed in future fusion power plants. First-principle modelling of edge plasma turbulence is therefore a key area of research in the fusion community, as it allows to extrapolate from present day experiments to future tokamaks.
Inspired by the hierarchy of models used to simulate turbulence in the neutral fluid community, the SOLEDGE3X fluid code incorporates a broad range of models with varying fidelity [1], which allows a stage approach analysis to the problem of edge turbulence. These range from empirical diffusivities, which are used to perform so-called "transport" simulations, to full-scale 3D first-principle turbulence modelling, where turbulent structures are self-consistently simulated. In between, a reduced approach inspired by the k-epsilon model [2], widely used in the computational fluid dynamics community, is proposed to capture key features of edge plasma turbulence and incorporate them into transport simulations [3]. Specifically, the growth of the turbulent energy "k" is governed by the primary interchange and drift wave instabilities, while turbulence saturation is achieved through a semi-empirical closure based on scaling laws [4]. Such approach allows for a quick assessment of the main turbulent characteristics of the plasma edge.
In this contribution, we present a direct comparison of the various approaches to model TCV and WEST edge plasma transport and turbulence, ranging from empirical transport modelling, transport modelling with k-epsilon prediction, and first-principle modelling. The fluctuation levels and cross-field transport predicted by the k-epsilon model is directly compared with first-principle simulations and experimental measurements. Interestingly, the k-epsilon model is able to recover not only the ballooned feature of radial transport at the outer midplane but also an increased radial transport along the divertor leg. A special focus will be put on comparing the behaviour of divertor localized filaments observed experimentally in TCV with fast cameras and recovered by 3D turbulence modelling [5].
[1] H. Bufferand et al., Nucl. Fusion 61 (2021), 116052
[2] W.P. Jones, B.E. Launder, Int. J. Heat Mass Transfer 15, (1972), 301
[3] S. Baschetti et al., Nucl. Fusion 61 (2021), 106020
[4] R.J. Goldston et al Nucl. Fusion 52 (2012), 013009
[5] H. Bufferand et al., Nucl. Mat. Energy 41 (2024), 101824
