AbstractThis Ph.D. thesis contains theoretical and experimental work on plasma turbulence measurements using collective light scattering.
The motivation for measuring turbulence in hot fusion plasmas is, along with the method used and results obtained, the subject of chapter 1.
The theoretical part is divided into three chapters. Chapter 2 contains a full analytical derivation of the expected dependency of the detected signal on plasma parameters. Thereafter, spatial resolution of the measurements using different methods is treated in chapter 3. Finally, the spectral analysis tools used later in the thesis are described and illustrated in chapter 4.
The experimental part is divided into four chapters. In chapter 5 transport concepts relevant to the thesis are outlined.
Main parameters of the Wendelstein 7-AS (W7-AS) stellarator in which measurements were made are collected in chapter 6. The setup used to study fluctuations in the electron density of W7-AS plasmas is covered in chapter 7. This localised turbulence scattering (LOTUS) diagnostic is based on a CO2 laser radiating at a wavelength of 10.59 µm. Fast, heterodyne, dual volume detection at variable wavenumbers between 14 and 62 cm-1 is performed. The central chapter of the thesis, chapter 8, contains an analysis of the measured density fluctuations before, during and after several confinement transition types. The aim was to achieve a better understanding of the connection between turbulence and the confinement quality of the plasma.
Conclusions and suggestions for further work are summarised in chapter 9. |