Core Impurity Spectroscopy in a Complex Mixed-Species Environment*

Identification and quantification of core impurity species with the Survey, Poor Resolution, Extended Domain (SPRED) extreme and vacuum ultraviolet spectrometer has been enhanced with novel higher-speed imaging cameras, and new spectral analysis techniques proven to be valuable in complex multi-species plasmas. The SPRED diagnostic has been critical in identifying perturbative radiative species, which has already motivated a vacuum vent to clean the vessel. Recent operation of SPRED has led to identification of over two dozen impurity elements in DIII-D, often the minority – most intentional and with known sources, but others unintentional and whose sources have been a mystery. In such a rich species environment, overlap of emission lines in the spectrum measured by a low-resolution (0.4-1.0 A optical FWHM) instrument is inevitable. Fitting of multiple overlapping emissions with careful wavelength calibration and a flexible multi-element Gaussian fitter has been carried out, leading to improved identification and quantification of individual species, and helping prevent misidentification. Core SPRED has also been refurbished with new high voltage power supplies for the multi-channel plates, and novel NMOS-based 1D detectors. Status and plans for core SPRED and the data provided to the DIII-D operations and scientific teams are shown.