Formation of flat electron density profiles at the L-2M stellarator at high ECRH powers

Abstract

The shapes of the electron temperature profiles were analyzed at the L-2M stellarator based on the data obtained in experiments on the axial ECR plasma heating performed at different plasma densities and heating powers. It was ascertained that, at the reduced ECRH power exceeding some threshold value, the electron temperature profiles become broadened and flat in the axial region of the plasma column. The appearance of the flat temperature profiles correlates with the occurrence of the density profiles with a dip in the axial region forming at high reduced heating powers as a result of the density pump-out effect. It was concluded that, as a result of occurrence of the density profiles with a dip in the axial region, the mechanism for the microwave radiation absorption changes. Apparently, the cyclotron absorption of the electron Bernstein waves becomes the main mechanism for the microwave radiation absorption, which, in turn, results in the occurrence of the broad and flat (in the axial region) electron temperature profiles.