Integrated core-SOL modelling of JET deuterium-tritium baseline plasmas

This thesis falls within the research field of nuclear fusion and tokamaks, representing a contribution to the exploration of a crucial issue for these fusion devices. This thesis deals with the characterization of the tungsten sputtering from the tokamak walls in a particular operational scenario, called baseline scenario, realized at JET, the largest magnetic fusion device in the world located Culham Centre for Fusion Energy in Oxfordshire, UK. This scenario was realized in preparation for the last experimental campaign in deuterium-tritium conducted at JET in 2021. Sputtering is one of the physical phenomena through which tungsten contaminates the plasma and disperses its energy. Tungsten has been selected as one of the materials for the new walls in JET, referred to as ITER-like walls, due to its exceptional physical properties. The primary objective of this thesis is to characterize the tungsten sputtering source, analyzing how it varies based on the isotopic species present in the main gas, namely deuterium, tritium, or a deuterium-tritium mixture. This study takes into account the phases that occur between and during the Edge Localized Modes (ELMs), which are instabilities that occur at the edge of the plasma. ELMs allow for the expulsion of impurities from the plasma, but at the same time, they cause the sputtering of these impurities from the walls, reintroducing them into the plasma. Consequently, the analysis of sputtering must consider at the same time the dynamics of ELMs. To conduct the analysis of the tungsten sputtering source as a function of different isotopic species and the dynamics of ELMs, an integrated modelling approach with the suite of codes JINTRAC was used. The results obtained in this thesis have shown that sputtering increases with isotopic mass, and the plasma core remains largely unaffected by this dynamic while the impurities tend to accumulate at the plasma edge. Other secondary results were obtained and are discussed throughout the thesis. The work was accompanied by the validation of the simulations by comparing the results with experimental data, ensuring the reliability and replicability of the findings obtained.