Linear gyrokinetic stability calculations of electron heat dominated plasmas in ASDEX Upgrade

Linear gyrokinetic calculations of low density electron heat dominated plasmas in ASDEX Upgrade [O. Gruber, H.-S. Bosch, S. Gunter et al., Nucl. Fusion 39, 1321 (1999)] are presented. It is found that the dominant mode is a trapped electron mode, which under the experimental conditions is sensitive to the density gradient, collisions, and magnetic shear. The quasilinear heat flux scales in good agreement with the experimental observed heat conductivity. Many experimentally observed phenomena can be explained on the basis of the presented calculations: the existence of a threshold, the fast propagation of the heat wave, and the moderate stiffness of the electron channel. The implications of the calculations for the empirical investigations are discussed.