Development of an experimental database of EUV spectra from highly charged ions of medium to high Z elements in the Large Helical Device plasmas

We are developing an experimental database of extreme ultraviolet spectra from highly charged ions using optically thin high‐temperature plasmas produced in the Large Helical Device. Spectra from a variety of elements with atomic numbers ranging from 36 to 83 have been systematically recorded in the range of 1–20 nm by a grazing incidence spectrometer. For higher Z elements from tin onward, discrete or quasicontinuum spectral features from n =4 ( N ‐shell) ions are mainly observed depending upon the plasma temperature, which leads to some new experimental identifications of spectral lines. On the other hand, major emitters are n =3 ( M ‐shell) ions for medium Z elements from krypton to ruthenium. The calculated wavelengths for Δ n ≠0 transitions agree well with the measurements and the calculated wavelengths are systematically shifted to shorter wavelengths for Δ n =0 transitions associated with inner‐subshell excited configurations.