Characteristic features of density fluctuations associated with the L-H-transition in the ASDEX tokamak

A far-infrared laser system was used to scatter from electron density fluctuations in the ASDEX tokamak. Particular emphasis was placed on the L-H transition which is characterized by the establishment of a transport barrier close to the separatrix. The difference in the behaviour of the fluctuations inside and outside this barrier was investigated. Another topic was the determination of plasma rotation from the measured frequency and wavenumber spectra. A number of diagnostics measuring macroscopic plasma parameters was recorded with sampling rates up to 5 MHz to investigate a possible relationship with the density fluctuations. (orig.)