Study of impurity ion transport using charge exchange spectroscopy on TCV

The study of impurity transport in fusion plasmas has gained interest over the years due to its implication with tokamak performances. In TCV (Tokamak à Configuration Variable), as in many other facilities, impurity ions can be studied through the CXRS (Charge Exchange Recombination Spectroscopy) diagnostic. The following research plan first presents the principles of CXRS. The main components of the diagnostic are described, as well as the data analysis methods used to infer ion temperature, density and velocity radial profiles. One of the main goals of the thesis is to measure accurate density profiles. Many transport models, in fact, are still developed without a consistent prediction of the density profile, which in many cases is assumed flat. In recent years, however, experiments have been performed to study ion transport in various plasma scenarios with the aim of providing a conncetion between theoretical predictions and actual measurements. This works present a study of impurity transport in negative triangularity. A large part of the thesis is dedicated to the investigation of the LOC/SOC transition and the rotation reversal, two phenomena often observed during density ramps that, in specific cases, appear to occur at the same critical density. This work shows a clear separation of the two phenomena, with an extensive study performed in discharges of different majority species (D, H, He), plasma configurations and shapes (limited, diverted, positive and negative triangularity).