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The concept of energy production through the fusion of two light nuclei has been studied since the 1950'. The main goal of controlled thermonuclear fusion research is to achieve a high density and high temperature plasma for a long confinement time. The most common way to confine the plasma is the tokamak. In the tokamak the energy and particle loss was found to be much larger than the neoclassical transport and is called anomalous transport. Today is commonly accepted that anomalous transport is due to microinstabilities driven by temperature and density inhomogeneities. The present Thesis is centered on the study of two major microinstabilities, trapped electron mode (TEM) and ion temperature gradient (ITG).
In studying the microinstabilities, first a linear gyrokinetic code, GS2, was applied to ASDEX Upgrade L-mode discharges heated with Electron Cyclotron Heating. The most unstable mode is found to be the TEM. The scan performed around the parameters obtained from the experiment has revealed that the growth rate of the mode depends on several plasma parameters that are not usually considered when analyzing the experiments, such as the density gradient length, R=Lne, and collisions. The direct comparison of the observed heat °ux with results obtained using quasi-linear theoretical calculations shows a good agreement. Both, the experiments as well as calculations show that there is a threshold for the TEM. The normalized growth rate obtained from the gyro-kinetic stability calculations has been also compared with Weiland and GLF23 models. A relative good agreement has been found between GS2 and GLF23 models, whereas the Weiland model performs less well (especially the shear dependence).

Additional information

Authors: SERBU M, Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, Garching (DE)
Bibliographic Reference: Garching: Max-Planck-Institut für Plasmaphysik, 2004. 139 pp Free of charge
Availability: The document can be downloaded at:
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