Poloidal correlation reflectometry at W7-X: radial electric field and coherent fluctuations

Poloidal correlation reflectometry measurements during the first plasma campaign of the optimized stellarator Wendelstein-7X are presented. The radial electric field is determined and a comparison with neoclassical calculations and shows good qualitative agreement. The measured density fluctuation spectrum exhibits coherent low-and high-frequency modes. Magnetohydrodynamic (MHD) modeling results suggest that the coherent fluctuations are caused by stable MHD-modes and Alfven waves.