First Results from the High-Field Side Scrape-Off Layer Reflectometer on DIII-D

A high-field-side (HFS) scrape-off layer (SOL) reflectometer has recently been designed and installed on the DIII-D tokamak. The reflectometer will provide the HFS SOL density profile with high spatial and temporal resolution, operating in the 6-27 GHz range in O-mode polarization, corresponding to a density range of approximately $4 \times 10^{17}$ - $9 \times 10^{18} m^{-3}$. To fit within the extremely limited space of the HFS, the reflectometer utilizes novel compact double ridged rectangular horn antennas designed specifically for the reflectometer measurement, which were 3D printed from a high temperature copper alloy, GrCop-84. The diagnostic is obtaining data on DIII-D with installation and calibration completed in early 2022. The primary mission of this diagnostic is the characterization of the HFS SOL for lower hybrid current drive (LHCD) coupling studies as the SOL conditions play a critical role in LHCD performance. Additionally, the reflectometer is capable of other SOL studies, such as anisotropy between the low-field and high-field sides. The design of the reflectometer as well as the first experimental results will be presented.