Divertor Plasma Conditions and Their Effect on Carbon Migration in the ASDEX Upgrade Tokamak (Diverttorin Plasmaolosuhteet ja Niiden Vaikutus Hiilen Kulkeutumiseen ASDEX Upgrade -Tokamakissa)

摘要

Divertors play a critical role in power and particle exhaust and plasma-material interaction in tokamaks. Of particular concern is the release of impurities from the material components, which reduces the lifetime of the vessel wall and affects the fusion performance. Furthermore, impurities with low charge number can migrate and re-deposit forming potentially tritium-rich layers in the tokamak. Sophisticated numerical simulations are required to understand how the various complex and often nonlinear processes in the plasma boundary affect the divertor performance. This thesis investigates the plasma conditions and the migration of impurities in the divertor region, using numerical code packages with the most complete available description of the relevant physical processes. It is known from earlier studies that the codes have both weaknesses and uncertainties in their models, which limits our current predictive capabilities. In this thesis work, carbon injection experiments at the ASDEX Upgrade tokamak are modelled. The work assesses the present-day boundary plasma models and elucidates impurity migration processes by comparing the simulations with experimental data.