Impurity modelling and transport coefficient reconstruction in tokamak core plasmas

Le résumé fourni par la source

Abstract The developed KAIST impurity modelling (KIM) code analyses impurity transport in the poloidal cross-section of tokamak plasma in both prediction and reconstruction modes. The prediction mode utilizes a numerical solution of the one-dimensional radial continuity equation to simulate impurity transport based on the given plasma parameters and extends the resulting radial impurity density distribution to a two-dimensional poloidal distribution by incorporating centrifugal-force-driven asymmetry. Synthetic diagnostic data, such as radiation power distribution and spectral emissions, are generated using atomic databases for direct comparison with experimental measurements. In reconstruction mode, the code reconstructs the impurity transport coefficient profiles from the experimentally obtained impurity density evolution over time, to overcome the limitations of forward-modelling-based transport coefficient inference. The developed reconstruction algorithm is based on numerical impurity flux calculations and Bayesian techniques and was validated using six reference impurity transport coefficient profiles from the KSTAR, JET, and ASDEX-U tokamaks. The reconstruction accuracy evaluated using the R 2 value, demonstrated good agreement ( R 2 > 0.87) between the reconstructed and reference profiles in the core regions ( r / a < 0.8), even in the presence of 5% random noise. The code was applied to a stationary KSTAR H-mode discharge to demonstrate its capability in analysing experimental W transport. The reconstructed transport coefficients were compared with neoclassical predictions to assess their physical validity. The results show that the total diffusion coefficient follows a radial trend similar to the neoclassical prediction but at a higher level consistent with the expectation of turbulent transport enhancement. This trend confirms that the KIM code yields physically reasonable transport coefficients from experimental data. This study details the theoretical framework, numerical validation, and experimental efficacy of the KIM code in advancing impurity transport research.

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