Integrated Modelling and Scenario Development in Tokamak Devices

This thesis concludes a three-year research programme within the PhD Programme in Fusion Science and Engineering, jointly organised by the University of Padova and the University of Naples Federico II, with the operational headquarters at Consorzio RFX, Padova. Consorzio RFX provided an inspiring environment that fostered scientific growth, enabling research on integrated modelling and scenario development for tokamak devices. Plasma behaviour is intrinsically non-linear, with strong couplings between heat, particles, momentum, current, and magnetic geometry. Integrated modelling frameworks address this complexity by coupling transport solvers, source and sink models, and equilibrium reconstruction, thus enabling predictive simulations of plasma evolution. These tools are crucial for disentangling causal relationships and validating them against experiments. A major part of this work focused on the Deuterium–Tritium Experimental campaigns, DTE2 (2021) and DTE3 (2023), at JET, which were analysed with the code TRANSP. These campaigns offered a unique opportunity to investigate reactor-relevant physics while validating modelling tools. In Chapter 5, JET pulses #99512 (DTE2) and #104661 (DTE3) were compared. TRANSP simulations, which included impurity dilution and deuterium accumulation, explained the absence of neutron yield enhancement in DTE3, despite 25% more auxiliary heating. Chapter 7 reports interpretative TRANSP studies were performed on JET D, T, and DT plasmas from the DTE2 and DTE3 campaigns, providing valuable insights into fast-ion physics and neutron production. Sensitivity scans on effective charge, density calibration, and NBI power highlighted their impact on predicted neutron rates. Predictive TRANSP–TGLF simulations of the JET D baseline scenario demonstrated the importance of pedestal ion temperature and particle source strength in reproducing experimental performance. The comparison of ELM-averaged and pre-ELM fits confirmed that pedestal shape and gradients affect neutron yield predictions. Finally, particle ion transport effects were shown to be an important element in modelling DT plasmas, with deuterium accumulation in the core improving agreement with experimental measurements and highlighting the necessity of including isotope-specific transport in predictive scenario development for future devices. The second major activity concerned the development of a hybrid scenario for the Divertor Tokamak Test facility (DTT), under construction in Frascati. Scenario development defines actuator trajectories (heating, current drive, fuelling, and coils) to achieve and sustain high-performance plasmas within operational limits such as density, power exhaust, and MHD stability. Using ASTRA coupled with TGLF, Chapter 6 presents self-consistent predictions for the evolution of density, temperature, and current. The current ramp-up phase was optimised to produce a broad current profile with low magnetic shear, enhancing resilience to MHD-induced confinement degradation. Different methods were tested, including ohmic ramp-up with or without current overshoot, and EC-assisted ramp-up with or without current drive. An integrated solution was identified, maximising the probability of success for experiments. The flat-top phase was also analysed to optimise the L–H transition and maximise performance under DTT constraints. Simulations under full auxiliary heating reproduced profiles that yielded a q-profile typical of hybrid scenarios, achieving a high normalised beta and good confinement. Overall, these results validate workflows for predictive scenario development, provide interpretation of JET DT results, and establish a robust basis for the first hybrid scenario studies in DTT, supporting optimisation strategies for future experiments.