Publication
Nuclear fusion provides a potentially unlimited and clean energy source which motivates the development of fusion power plants. The tokamak is one of the most promising concepts for a future reactor, confining the fusion plasmas in a torus using strong magnetic fields. A significant fraction of the heating power required to maintain fusion reaction is persistently transported by plasma across the magnetic flux surface into a thin, open-field-line region called scrape-off layer (SOL), where the power is driven towards the divertor target following the magnetic field lines. Unmitigated heat fluxes at the targets would far exceed the acceptable material limits, causing serious plasma exhaust issue that could possibly be solved by operating the tokamak in a detached regime, characterized by low plasma temperatures in front of the targets and reduced particle fluxes. This thesis contributes to the development of fusion energy with the SOLPS-ITER code and experiments in the TCV tokamak, focusing on the reduction of plasma exhaust on the divertor target using impurity-seeded detachment in single-null (SN) and other divertor geometries. Injecting impurity neutrals such as nitrogen, neon, and argon could transfer a portion of the SOL heat flux into radiation, which distributes power more evenly across the vessel wall rather than concentrating it on the target plates. However, excessive impurity penetration into the core region in turn degrades the confinement or even leads to a radiative collapse. The impurity transport to the core could be controlled by introducing gas baffles which increases both the deuterium and the impurity neutral concentration in the divertor and enhance the momentum and power loss. The proposed tightly baffled, long-legged divertor configuration promises an even better performance and a passively stable, fully detached regimes. The first issue, addressed in this thesis, is the nitrogen-seeded detachment in both L-mode and H-mode.. The simulations in the first year agree well with the trends observed in TCV experiments in L-mode discharges, , though the simulation predicts a colder and denser divertor. Stringent comparison between SOLPS simulation and TCV experiments in H-mode will be made, in additional to the X-point radiator in H-mode discharges. Alternative divertor geometries including baffles and long-legged divertor will also be included in simulation to test their influences on the impurity seeding. The comparison with experiment requires the development of ASDEX-type pressure gauge (APG) which measures the neutral pressures in a variety of locations in the TCV chamber, from which the neutral compression is calculated. The APGs have been tested in vacuum chamber without fusion plasma in the first year, and are currently being installed in TCV. The data acquisition and storage, gauge calibration, operation in impurity-seeded discharges will be further developed during the thesis research. The results obtained in the fir