报告人:Ian Faust, Ph.D.
Spectroscopic line characteristics can often be directly determined from a line’s charge state and emissivity using EBIT machines or specific tokamak conditions. However, such experiments require specialized hardware or dedicated experiments for the calculations. An alternative characterization method was developed by indirectly inferring the charge state by comparing the observed unknown line intensity to a line of known charge state. The two were related through the calculated plasma tungsten concentration (cW). A meta-analysis approach using a wide set of plasma conditions and experiments allowed for cross-validation statistical methods to be applied, creating a framework by which the line-integrated spectral phenomena could be rigorously correlated. The electron temperature dependence of an unknown tungsten line in .39-.4 nm wavelength range was determined using these techniques on ASDEX-Upgrade. This wavelength range is widely used worldwide for argon-measuring Imaging X-ray Spectrometer (XICS) systems, and this line could provide a new pat to spatially-resolved core tungsten measurements. Using machine learning methods and comparisons to ADAS results, the electron temperature dependency consistently matched that of a copper-like tungsten line. While the results of the qualitative charge state comparison is clear, the related quantitative uncertainty of the regression was high. The utility of older spectrometers in impurity characterization can be thereby improved with minimal dedicated experimentation when the meta-analysis approach is used with computational results. Therefore, this scheme is most practical in cases where direct experimentation is costly but indirectly-related data is common, which will likely be the case in future fusion devices.
From 2016-2018, Ian worked as a post-doctoral researcher at the Max Planck Institute for Plasma Physics in Garching, Germany under Dr. Ralph Dux. During that time, his work focused on experimental EUV and X-ray impurity spectral measurements on the ASDEX-Upgrade tokamak. Before that, he completed his doctorate at the MIT PSFC from 2009-2016 with his thesis titled 'Quantification of Lower Hybrid wave absorption in the edge of the Alcator C-Mod tokamak' under professors Dennis Whyte and Ronald Parker.