A high resolution VUV spectrometer for study of radiated power in the tokamak divertor

A high resolution (HR) vacuum ultraviolet spectrometer with sub-1 Angstrom optical resolution has been designed, installed, and successfully operated on the DIII-D tokamak for study of the power radiated by emission lines and molecular bands at VUV and UV wavelengths in the divertor. The HR-VUV diagnostic was utilized in plasma discharges spanning the attached to fully-detached divertor regimes, revealing trends in the carbon ion and neutral deuterium emissions. Capable of monitoring the 110-600 nm range, the instrument is designed with a 445 mm focal length in a Czerny-Turner configuration with Al/MgF₂-coated mirrors and VUV-optimized gratings and a VUV-phosphor-coated detector. It is enclosed in a lightweight 316-stainless steel vacuum vessel for low magnetic permeability to operate near the machine magnetic field. The spectrometer includes three gratings to provide both survey (~50 nm bandwidth) capability as well as narrow, high resolution (<10 nm) capability for study of nearby emissions and molecular band structure. Data from the diagnostic and the impacts of radiation on the unshielded camera will be shown, as well as future improvements discussed.