Investigation of Lower Hybrid Wave Interaction with the Edge Plasma in WEST through Electric Field Vector Measurements

The WEST tokamak’s main mission requires it to establish and sustain long pulse H-mode operation in an all-W wall environment using only RF waves for heating and current drive. To drive plasma current, two lower hybrid (LH) launchers are installed and operate at 3.7 GHz with a combined power of up to 7 MW for 1000 s. A new experimental arrangement on WEST aims to measure the spatially resolved LH wave electric field vector, $\mathbf{E}_{LH}$, in front of one of these launchers. The main motivation is to improve understanding of LH wave interaction with the scrape off layer (SOL) plasma. The experimental measurement of $\mathbf{E}_{LH}$ is obtained by fitting the Schr\"{o}dinger equation to the $\sigma$-polarized ($\perp$ to $\mathbf{B}$) $D_{\beta}$ spectral line profile. The $D_{\beta}$ spectrum are acquired passively from optical emission observed near the lateral protection limiters. The measured $\mathbf{E}_{LH}$ is then systematically compared to simulations using a 3D full-wave COMSOL model. Details of the experimental arrangement will be described and initial $\mathbf{E}_{LH}$ results will be presented. Future work focused on studying $\mathbf{E}_{LH}$ as a function of LH power, confinement mode, Greenwald fraction, and magnetic geometry will be discussed.