Abstract We have constructed collisional-radiative (CR) models for tungsten ions, W q+ , with q = 18–25, including ionizing and recombining processes as well as collisional excitation/deexcitation and radiative decay, and applied the models to analyze extreme ultraviolet (EUV) spectra measured in magnetically confined fusion plasmas with a tungsten pellet injection into the Large Helical Device (LHD). The CR models are constructed as hybrids with fine-structure levels for lower states and relativistic configuration-averaged levels for higher states to include autoionizing states. The dielectronic recombination process is treated as dielectronic capture to the autoionizing states and radiative decay from the autoionizing states in the CR model. We calculated EUV spectra of the tungsten ions for ionizing and recombining plasmas. Measured spectra at the 2–4 nm region were used to estimate the charge state distribution of tungsten ions in LHD plasmas by comparing calculated emission peaks of n = 4–5 transitions of W q+ with q = 22–25. Using the estimated ion distribution, the synthesized spectral profile at 4.5–7 nm shows characteristic profiles similar to the measured so-called unresolved transition array (UTA) due to n = 4–4 transitions. We also synthesized the spectra at 10–35 nm, where the UTA due to n = 5–5 transitions appeared, and we partly reproduced the UTA with synthesized spectra. The CR models for the tungsten ions were validated with the measured spectra of LHD plasmas.
Murakami et al. (Wed,) studied this question.