Advances in Low-Temperature Tungsten Spectroscopy Capability to Quantify DIII-D Divertor Erosion

Recent emphasis of tungsten (W) plasma-material interaction experiments on DIII-D has made it essential to enhance the W I and W II measurement capabilities of its spectroscopy diagnostic suite to acquire W sourcing measurements with high temporal, spatial, and wavelength resolution. To this end, four new viewing chords for the multichordal divertor spectrometer and divertor filterscope systems were installed, leading to a 7× increase in blue-light sensitivity. W I and low-Z impurity line identifications were performed in the 3995-4030 Å region, placing wavelengths within 0.1 Å of the National Institute of Standards and Technology values. A novel method was also developed for the DIII-D high-temporal resolution filterscopes to distinguish between W I light and background contamination, important due to the relatively weak intensity of this line, using two different bandpass filters with different widths but the same center wavelength. Finally, fast imaging of the W I 4008.75 Å spectral line with a PCO Pixelfly VGA 200/205 camera is allowed for discrimination between intra-edge-localized mode (ELM) and inter-ELM W I emission profiles with very high (~1 mm) spatial resolution.