Implementation of Doppler-Free Saturation Spectroscopy on the DIII-D Tokamak for RF Wave Field Measurements

Over the next several years, the operational space of two novel RF actuators designed for off-axis current drive will be extensively explored in the DIII-D tokamak. The goal of these programs is focused on evaluating the potential for efficient current drive in advanced tokamak scenarios. Previous experimental work on C-Mod and NSTX has determined that wave coupling with the scrape-off-layer (SOL) plasma can result in substantial core power loss. However, recent computational studies indicate that the SOL plasma can be optimized to minimize the undesired wave/SOL-plasma coupling. A diagnostic based on Doppler-free saturation spectroscopy (DFSS) was designed for direct measurement of the wave’s electric field vector (E_RF) in the edge plasma of DIII-D. The DFSS diagnostic was designed to provide a local measurement over a 2-D region with mm-scale spatial resolution and <10 V/cm electric field resolution. In this presentation, the DFSS diagnostics design and installation status will be presented.