Doppler line shape model for the W I 5d⁵6s—5d⁵6p transition at 400.9 nm in tokamaks

Tungsten (W) spectroscopy is known to be a useful tool for quantifying W fluxes in tokamaks. We aim to analyze how background plasma parameters influence the W spectral-line shape measured in the divertor and scrape-off layer and what information could be retrieved from such an analysis. To that end, a Monte Carlo model is developed to simulate the line shape of the 400.9 nm W I line emitted by physically sputtered W ions from plasma facing components. The influence of background plasma parameters (ion and electron temperature) and geometrical effects (detector positioning with respect to the eroded surface) are investigated. The effect of Zeeman splitting on the spectral line-shape is also explored. A set of requirements for the experimental set-up needed to measure the analyzed spectral line features with line peak shifts of the order of 10⁻²Å and peak widths in the range from 10⁻¹Å to 10⁻²Å are proposed. These requirements are shown to be experimentally accessible, through the installation of specific high-resolution spectrometers not typically used on magnetic fusion devices. (paper)