Modelling of high radiating regimes with Neon impurity seeding in the EU DEMO using the SOLPS-ITER code

In the need of a reliable and source of energy, nuclear fusion is becoming more and more attractive with its promise of being substantially unlimited and carbon-free while overcoming the safety concerns linked with the more traditional fission. In the EU DEMO, ITER’s successor which will prove the feasibility of future fusion power plants with the aim of producing electricity, one of the major challenges that must be overcome is the power and particles exhaust. In fact, due to its large size, the fluxes of energy and mass coming from the core plasma and auxiliary heating must be handed carefully to ensure a proper lifetime of the plasma facing components while guaranteeing a high availability of the plant. In particular, it is expected that a power around 170 MW must be exhausted in the Scrape-off Layer (SOL). It is thus of vital importance to explore plasma scenarios such as high radiating and divertor detachment regimes due to impurity seeding to avoid large power fluxes on the latter surfaces while keeping sufficiently low electron temperatures in front of them, to prevent material erosion and plasma contamination due to sputtering of the wall. Along with power scaling experiments and the knowledge that will derive from the ITER experience, computational simulations can play a key role in the design and plasma scenarios that will be operated in DEMO. In the present thesis work, the SOLPS-ITER code package is employed to carry out high radiating regimes simulations which mimic the conditions that will be present in DEMO. The first step of the proposed workflow is to build a computational grid of the problem considered through the DivGeo, a graphical tool available within the code package, and Carre, the grid generator. Then, once the case has been set up, it is converted in the unstructured version of the code, namely SOLPS-ITER 3.2.0 which will be exploited to perform the computational simulations. Moreover, the present work will be focused on the use of fluid neutrals, in particular the Advanced Fluid Neutral (AFN) model for the Deuterium atom developed by the KU Leuven Applied Mechanics and Energy conversion research group led by Professor M. Baelmans. Indeed, neutral particles are usually treated with a kinetic approach exploiting a Monte Carlo code which in the case of SOLPS-ITER is the EIRENE neutral transport code, while charged ones are described using a fluid transport model. The coupling of these two different treatments can introduce statistical noise that can complicate the convergence assessment of the solution while strongly increasing the computational time of the simulation as the plasma and neutral collisionality grows. Therefore, the need of fluid neutral models which can accurately describe the behavior of neutrals is fundamental. In this thesis, the simulations carried out concentrate on the seeding of Neon through gas puff varying the upstream density while acting on the pump albedo. The aim is to achieve divertor operational scenarios in which the power and particles fluxes and temperature are reduced by the onset of partially or fully detached regimes. Then the results obtained are compared to a parallel work in which the seeded impurity is Argon, carried out by Professor F. Subba at the Polytechnic of Turin, highlighting the main differences between the two selected species, and the relative consequences.