Electron Temperature Profiles Formed under Conditions of the Axial ECR Plasma Heating at the L-2M Stellarator

The shape is analyzed of the electron temperature profiles measured in experiments on the axial ECR heating at the L-2M stellarator at different densities and heating powers. It is ascertained that when the reduced ECR heating power exceeds some threshold value, the electron temperature profiles become broadened and flat in the core region of the plasma column. The correlation is revealed between the appearances of the flat temperature profiles and the density profiles with a dip in the axial region (the dip-shaped profiles) occurring as a result of the density pump-out effect. It is concluded that the appearance of the dip-shaped density profiles in the plasma results in a change in the mechanism of microwave radiation absorption. Hypothetically, the cyclotron absorption of the electron Bernstein waves becomes the dominant mechanism for the microwave radiation absorption that, in turn, results in the formation of the broad and flat (in the core region) electron temperature profiles.