Electron density profiles measurements by reflectometry in front of a lower hybrid launcher on WEST

Abstract This work aims to carry out the challenging measurement of electron density profiles in the vicinity of a radio-frequency tokamak heating system: the lower hybrid current drive launcher. Coupling efficiency of lower-hybrid (LH) waves with the plasma requires a precise knowledge of the local electron density which can be provided by a frequency swept reflectometer embedded into the LH launcher. This micro-wave diagnostic probes the plasma and receives the incident wave which has been phase-shifted during its propagation. An iterative method is used to retrieve radial electron density profiles from the acquired phase shifts. Special efforts are devoted to signal processing to minimize phase parasitic noise due to plasma turbulence and multiple reflections. The automation of this process enables the reconstruction of density profiles for an entire plasma discharge. A first study of the LH wave-plasma coupling efficiency is presented.