High-Resolution Ultraviolet Spectroscopy for Erosion Measurements of Plasma-Facing Components

To investigate high-Z impurity erosion and re-depostion, an upgraded UV spectrometer and probe have been installed on the Compact Toroidal Hybrid (CTH) experiment. Using spectroscopic measurements of impurity emission, erosion and re-deposition rates of plasma facing components can be quantified by using atomic physics coefficients (S/XBs) which relate spectral line intensities to material influx. Challenges arise from insufficiently resolved spectral lines due to impurity blending, pressure broadening, and Zeeman and hyperfine splitting, leading to erroneous inference of erosion rates. As such, a 1.33-meter focal length spectrometer with a high-resolution diffraction grating and UV optimized sCMOS camera has been developed, providing ~4 pm resolution for a ~3 nm spectroscopic window down to 200 nm. Impurity emission is produced by plasma interaction with a high-Z sample at end of a translatable probe. The upgraded probe system allows for faster sample changes while maintaining vacuum cleanliness and can extend the high-Z sample to the CTH magnetic axis. A single tip Langmuir probe measures the plasma electron temperature and density at the high-Z sample surface. First results of high-resolution tungsten spectra using the new probe and UV spectrometer in CTH will be presented.