Spectroscopy in the wavelength region of 330 nm to 400 nm for highly charged tungsten was performed using the High Temperature Super Conducting Electron Beam Ion Trap (SH-HtscEBIT) at Fudan University. Three lines from palladium-like tungsten (W 28+ ) were identified as transitions between metastable levels in the first excited configuration ([Kr]4d 9 4f). A secondorder relativistic many-body perturbation theory approach and a simple collisional radiative model were used to theoretically study the fine structure levels of the 4d 9 4f configuration. The calculated results show qualitative agreement with experiment. We conclude that some levels in the 4d 9 4f excited configuration have extremely long lifetimes and may exhibit extraordinarily high populations, possibly leading to indirect ionization in, for example, fusion plasmas.
Visible transitions of promethium-like tungsten (W13+) were studied using the Shanghai high temperature superconducting electron beam ion trap. The M1 transition between the ground state (4f135s2 2F) fine structure levels was measured to be at 549.95 ± 0.06 nm. Seven other lines from W13+ were also found and five of them were classified as belonging to transitions within the first excited configuration (4f125s25p). These lines were assigned with the help of relativistic configuration interaction calculations and collisional-radiative model predictions of the relative line intensities.
We present an overview of recent work on the spectroscopy of tungsten ions, related to tokamak edge plasma. The spectra were recorded from the newly-built low energy electron beam ion traps (EBITs) in the Shanghai EBIT laboratory. By analyzing the spectra with the help of accurate theoretical calculations, using state-of-the-art techniques, we were able to identify term and fine structure splittings in the ground and the first excited configuration for a number of charge states. The theoretical models included a careful study of correlation and showed an excellent agreement with our experimental results for transition energies and rates. Some metastable levels which have extremely long lifetime and high population were found, and the influences of these levels on the charge state distribution of tungsten ions in tokamaks are discussed.
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