Soft X-ray Spectra of Highly Charged Hf, Ta, W, and Au

We use our EBIT to measure wavelengths for highly-charged states of heavy elements for use in diagnostics of fusion-type plasmas, such as ITER. The range of our grazing-incidence spectrometer has been extended to below 2 nm to obtain overlap with our microcalorimeter. Our range of electron impact energies now spans 2-24 keV. We use atomic data generated by the FAC code and collisional-radiative modeling with the NOMAD code to interpret the observed spectra. Previously [1], we published wavelengths for Na-like, Mg-like, and Al-like ions of Hf(Z=72), Ta(Z=73), W(Z=74), and Au(Z=79) from 6.5 to 8.5 nm. We now measure wavelengths for these ions in the region 1.8 to 2.6 nm. Our preliminary values for the 3s$_{1/2}$-3p$_{3/2}$ transition in the Na-like ions are 2.5772(18) nm for Hf$^{61+}$, 2.4498(18) nm for Ta$^{62+}$, 2.3245(18) nm for W$^{63+}$, and 1.8059(22) nm for Au$^{68+}$. For these ions, the fine structure splitting of the D-line doublet is larger than the mean value of the transition energy. We observe this giant splitting directly in a single spectrum on our grazing-incidence spectrometer. [1]Yu. Ralchenko et al., J. Phys. B: At. Mol. Opt. Phys. \textbf{41}, 021003 (2008).