Estudo do plasma do diversor no COMPASS-D

This thesis presents a discussion of selected results from the edge plasma studies carried out on the COMPASS-D tokamak. Emphasis is placed upon the factors which affect the peak divertor heat flux, such as the SOL (scrape-off layer) width, transient increases in the heat flux during ELMs (edge localised modes) and asymmetries in the divertor target parameters. The main diagnostic used in this study is an array of Langmuir probes which provides localised measurements of the divertor plasma parameters with high spatial and temporal resolution. Transport in the divertor and SOL of COMPASS-D is investigated for a wide range of plasma conditions and results presented in chapter 4. With this aim, a database of SOL parameters has been established. Parallel transport is studied by comparing upstream and divertor profiles while cross-field transport is investigated studying how the SOL width scales with the main plasma parameters. Chapter 5 describes the analysis of high confinement (H-mode) discharges and the effect of ELMs on the divertor plasma parameters. L-and H-mode confinement is compared, emphasising the changes in the edge profiles and in the fluctuation levels. The temporal and spatial disturbances of the edge plasma associated with ELMs are also characterised and results show that those lead to high power transients to the divertor target. Finally, it is shown in chapter 6 that divertor target profiles are strongly influenced by the E x B drift, where the electric field is largely determined by the SOL current profileAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1249-074 Lisboa, Portugal / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga