Real-time modelling of DTT plasma scenarios using the RAPTOR transport simulator code

Controlled nuclear fusion is a promising solution to our current energy crisis that aims to provide clean energy without greenhouse gas emissions or long lasting highly radioactive waste production. Several projects are currently in development to obtain the knowledge necessary to build a commercially viable fusion power plant in the next decades, first and foremost the ITER reactor in construction in Cadarache (France) that will in turn pave the way for the following DEMO reactor, the first hopefully capable of net production of electrical energy. Despite the ambitious aims of ITER, it will not be able to fully explore several key physical and engineering aspects required for the subsequent generation of reactors. Among these of great importance is the design of their divertors: these devices are able to open the flux surfaces of the containment magnetic field in the reactor and by doing so redirect the flux of particles coming from the plasma toward suitable targets. Among the several advantages of this configuration is that the interaction between the plasma and the chamber wall is kept in a region separated from the core plasma, greatly reducing the influx of impurities, and that the power exhaust is directed toward a specific section of the wall that can thus be the only one designed to sustain extremely high energy fluxes. Despite their importance, ITER will not implement a divertor design suitable for the later DEMO and this brought forth the necessity for a dedicated experiment to study the viability of various divertor configurations in more demanding conditions. This experiment will be DTT (Divertor Tokamak Test), currently under construction at the ENEA Research Center in Frascati (Italy). To control the plasma dynamics, DTT will make use of an integrated approach that requires a faster-than-real-time physical modeling of the plasma, of which one key component is the simulation of transport phenomena and the corresponding radially dependent physical profiles of the plasma. This will be performed by a 1-dimensional simulator code optimized for control problems and rapid iteration called RAPTOR (RApid Plasma Transport simulatOR). The aim of this thesis is to validate RAPTOR in this application by simulating different plasma scenarios of DTT, following a full time evolution and with both low magnetic field and low externally injected power, as is expected to operate during its first years after commissioning, and with a full suite of external heating systems and higher fields that will be needed for the full scale test of DEMO-like divertor conditions. To improve the results and check their validity, our simulations have been confronted with those obtained with other codes, more specifically METIS, another fast transport simulation code, and ASTRA, a much more complex and computationally demanding simulator. RAPTOR also provides modeling of sawtooth instabilities, an important phenomena that results in periodic crashes of the core temperature of the plasma, caused by topological effects that trigger sudden changes of resistivity in the plasma. Characterizing these sawteeth and how their onset and period are affected by changes in the external heating is useful for controlling them and avoiding negative effects linked to the onset of other types of more problematic instabilities. A double sawtooth sweeping experiment, involving the variation of the radial deposition depth of the external sweeping system while monitoring the sawteeth's period, has been successfully simulated using RAPTOR, showing the robustness of its modelling of this kind of instability. RAPTOR has thus being tested in different ways in its ability to simulate scenarios that more closely model the actual operation conditions of DTT, paving the way for its future use both for integrated control of the experiment and for obtaining quick preliminary modeling results without using more time consuming codes.