Lower Hybrid Wave Electric Field Vector Measurements Using Non-Perturbative Dynamic Stark Effect Optical Spectroscopy on Alcator C-Mod

Plasma-wave interactions near the lower hybrid (LH) wave launcher can have a major impact on driven LH current, especially in the high-density regime. To identify the relevant physics responsible for this interaction a correlated effort of experimental measurements and simulations of the LH wave electric field vector, \textbf{E}$_{\mathrm{LH}}$, were carried out on Alcator C-Mod using the SELHF (Stark Effect Lower Hybrid Field) diagnostic and COMSOL modeling. For a range of plasma parameters observations show that: 1) The polarization \textbf{E}$_{\mathrm{LH}}$ resides primarily in the radial-poloidal plane and becomes increasingly poloidal for locations away and to the top of the LH launcher. 2) Saturation of the radial component of \textbf{E}$_{\mathrm{LH}}$ is observed at an LH power density of approximately 12 MW/m$^{\mathrm{2}}$. 3) Reflectometry phase fluctuations were found to be correlated with \textbar \textbf{E}$_{\mathrm{LH}}$\textbar . These results suggest that the LH resonance cone and power spectrum may be substantially modified near the LH launcher in the high-density regime from the expected radial polarization and square root scaling of the magnitude with LH power. Simulation of the experimental data was carried out through development of a synthetic diagnostic using a full wave cold plasma COMSOL model. Density fluctuations and reflectometry measured density profiles were incorporated. Without density fluctuations, the synthetic \textbf{E}$_{\mathrm{LH}}$ signal is dominantly in the radial direction and scales with the square root of LH power, as expected. Increasing density fluctuations in the model can cause the magnitude of \textbf{E}$_{\mathrm{LH}}$ to decrease substantially and greatly vary the direction of \textbf{E}$_{\mathrm{LH}}$. The observations and results outlined above will be presented in detail and the applicability of density fluctuations as a mechanism behind the behavior of \textbf{E}$_{\mathrm{LH}}$ will be discussed.