Lower hybrid electric field magnitude and polarization measurement and modeling results on the WEST tokamak *

Lower hybrid (LH) current drive is used to drive current and enable long pulse operation of advanced tokamak scenarios. This poster presents recent experimental and modeling results of the LH electric field magnitude and polarization in the scrape-off-layer (SOL) to better understand the coupling of LH waves through the SOL of the WEST tokamak. This is achieved using the DSELF dynamic Stark effect diagnostic to measure the LH electric field over 200+ discharges on WEST, combined with full-wave modeling and a synthetic DSELF diagnostic to validate models against experiments. Recent results show that the spatially averaged measured LH electric field magnitude is consistent with modeling over the experimental uncertainty. At some poloidal locations, the measured LH electric field is significantly different than expected from the model. For most discharges, the measured and modeled LH polarization agrees. However, on average, at higher densities and during MHD events, the measured LH polarization disagrees significantly with the model. These discharges with significant discrepancy in the LH polarization measurement and model appear to be correlated with reduced LHCD efficiency. Hypotheses such as density fluctuations to explain these discrepancies will be discussed.