Validation of tungsten erosion and transport simulations in tokamaks

This dissertation evaluates the validity and options for improvement of simulation codes in predicting tungsten erosion and transport in tokamaks, by code-code comparisons and validation against measurements from JET and ASDEX Upgrade experiments. Tungsten is a leading candidate as the plasma-facing material in magnetic confinement fusion power plants. However, W contamination of the fusion plasma is highly detrimental to reactor performance and impedes the attainment of viable power production. The ability to predict the erosion rate of W components and the resulting W density in the plasma is crucial for designing fusion reactors. The simulations studied in this thesis predict the sputtering of W atoms from plasma-facing components, their ionisation in the scrape-off layer, and the transport of W ions parallel and perpendicular to the magnetic field in the scrape-off layer, pedestal, and core plasma regions. In this thesis, the predicted W erosion rate at the JET divertor targets is found to have a negligible impact on the W density in the main plasma due to efficient divertor screening. According to EDGE2D-EIRENE, DIVIMP, and ERO2.0 predictions, the W influx to the main plasma is predominately due to W sputtering near the low-field side divertor entrance due to energetic D atoms created by charge-exchange. EDGE2D-EIRENE consistently predicts 30--40% lower W density in the main plasma compared to DIVIMP in both L-mode and H-mode plasmas. In this work, the difference is demonstrated to be mostly due to the bundling of the 74 W ionised charge states into 6 fluid species in EDGE2D-EIRENE. Integrated core-edge JINTRAC predictions agree with measurements of the main plasma W density in L-mode, indicating that both the DIVIMP and EDGE2D-EIRENE predictions are consistent with the experimentally inferred W density within a factor of 2. Simulations of high-power type-I ELMy H-mode plasmas, using ERO2.0 for W erosion and transport in the edge plasma and JINTRAC with NEO for core W transport, predict the 2D poloidal W density profile in agreement with the inferred W density within the modelling uncertainties. Accurate predictions of the main plasma W density in type-I ELMy H-mode require thorough validation of the simulated ELM and edge transport barrier properties, as well as precise reproduction of the toroidal rotation frequency, and the ion temperature and density gradients in the main plasma.