Modeling of high-resolution Kα emission spectra from Fe XVIII through Fe XXIV

Results for Kα x-ray emission from highly charged iron ions, which were obtained from a detailed and systematic spectral model, are presented in the wavelength range from 1.84 to 1.94 {}. Account has been taken of the fundamental atomic radiative-emission processes associated with inner-shell electron collisional excitation, inner-shell electron collisional ionization, as well as dielectronic recombination. Particular emphasis has been directed at the identification of spectral features that can serve as diagnostics of extreme nonequilibrium or transient-ionization conditions, which can occur in stellar flares and supernova remnants, as well as in tokamak plasmas. In order to investigate the fundamental Kα line-formation processes that can play a dominant role under these conditions, theoretical predictions have been compared with spectral observations of the EBIT-II x-ray emission from highly charged Fe ions in the electron-beam ion trap at the Lawrence Livermore National Laboratory. The observed spectroscopic features are found to be well represented by our theoretical calculations, validating earlier theoretical work on transient-ionization phenomena. We have identified spectral features that can serve as diagnostics of the electron density, the line-formation mechanism, and the charge-state distribution.