Applications of advanced kinetic collisional radiative modeling and Bremsstrahlung emission to quantitative impurity analysis on the National Spherical Torus Experiment

An advanced kinetic collisional radiative model is used to predict beam into plasma charge-exchange visible and extreme UV (XUV 50-700 Å) light emission to quantify impurity density profiles on NSTX. This kinetic model is first benchmarked by predicting line-of-sight integrated emission for the visible λ = 5292.0 Å line of carbon (C VI n = 8 → 7), and comparing these predictions to absolute calibrated measurements from the active CHarge-Exchange Recombination Spectroscopy diagnostic (CHERS) on NSTX. Once benchmarked, the model is used to predict charge-exchange emission for the 182.1 Å line of carbon (C VI n = 3 → 2) that is used to scale Bremsstrahlung continuum emission in the UV/XUV region. The scaled Bremsstrahlung emission is used as a base to estimate an absolute intensity calibration curve of a XUV Transmission Grating-based Imaging Spectrometer (TGIS) diagnostic installed on the National Spherical Torus Experiment (NSTX and upgrade NSTX-U). The TGIS diagnostic operates in the wavelength region 50-700 Å, and it is used to measure impurity spectra from charge-exchange emission. Impurity densities are estimated by fitting synthetic emission from the kinetic charge-exchange model to TGIS spectral measurements.