Abstract:We present a direct observation of the M1 transition between the fine structure splitting in the 4 f 13 5s 2 5p 6 2 F ground term of W VIII. The spectroscopic data of few-times ionized tungsten ions are important for the future ITER diagnostics, but there is a serious lack of data. The present study is part of an ongoing effort to solve this problem. Emission from the tungsten ions produced and trapped in a compact electron beam ion trap is observed with a Czerny-Turner visible spectrometer. Spectra in the EUV range are also observed at the same time to help identify the previously-unreported visible lines. The observed wavelength 574.47 ± 0.03 nm (air), which corresponds to the fine structure splitting of 17,402.5 ± 0.9 cm −1 , shows reasonable agreement with the previously reported value 17,410 ± 5 cm −1 obtained indirectly through the analysis of EUV spectra [Ryabtsev et al., Atoms 3 (2015) 273].

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We present the investigation of new visible lines for W 8+ and W 9+ from the spectra observed using an electron beam ion trap. The analysis is based on the collisional-radiative (CR) modeling with fine-structure sublevels population kinetics. To ensure the identification of lines done by the CR model, we have also performed the accurate calculation of transition energies and transition probabilities within multi configurational Dirac-Fock using the GRASP2018. In the spectrum, most of the observed lines are assigned as magnetic dipole (M1) transitions belonging to the first two lower-lying configurations of these ions.