Nuclear fusion, with its potential to provide a nearly unlimited energy source, has inspired scientists to work on the development of fusion power plants. Among the various devices designed to harness nuclear fusion, the tokamak confines the fusion fuel, which has to reach high temperatures for fusion reactions to occur and enters the plasma state, using strong magnetic fields. However, the magnetic confinement is not perfect and plasma particles and energy reach the outermost chamber region, the Scrape-Off-Layer (SOL), where magnetic field lines intersect the material surface, and ultimately reach the wall. In current reactor designs, unmitigated peak heat fluxes would greatly exceed the material limit and a safe power removal from the plasma must be attained for successful operations of fusion reactors. The entire plasma dynamics of the SOL plays a fundamental role in determining the plasma exhaust. To understand its critical aspects and extrapolate from today's experiments to future fusion reactors, several numerical codes modelling the plasma edge have been developed.
This doctoral thesis seeks to improve the understanding of divertor power exhaust by studying the effect of particle drifts on the SOL transport. The investigation of particle drift-related transport is carried out using the SOLPS-ITER code for the plasma edge and experiments at the TCV tokamak. The thesis thus contributes to the validation of the SOLPS-ITER drift model. Simulations and experiments are carried reversing the magnetic field direction, as the particle drift direction depends on it, and are compared employing numerous diagnostics, with particular focus on the Infrared thermography system. Part of this work is devoted to the improvement of the IR system, whose analysis was improved as part of this thesis.
Particle drifts are found to significantly affect plasma conditions in the divertor, contributing significantly to the particle and convective heat fluxes. The importance of drifts is found to increase with increasing divertor plasma temperature. The diamagnetic drift is responsible for the dominant cross-field current in the SOL. The E×B drift is responsible for the in-out divertor redistribution of plasma density and power. Within the experimentally achieved density range, the radial E×B drift is identified as the dominant drift. Most of the experimental observations found with the field reversal are confirmed by drift simulations. However, a quantitative agreement between measurements and simulations cannot be achieved, with simulations generally predicting higher densities and lower temperatures in the divertor than experimentally observed. The comparison thereby guides future work to improve the experiments as well as the divertor model.