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We have measured the electron impact excitation cross sections for the strong iron L-shell 3 {yields} 2 lines of Fe XVIII to Fe XXIV at the EBIT-I electron beam ion trap using a crystal spectrometer and NASA-Goddard Space Flight Centers 6 x 6 pixel array microcalorimeter. The cross sections were determined by direct normalization to the well established cross section of radiative electron capture through a sophisticated model analysis which results in the excitation cross section for the strong Fe L-shell lines at multiple electron energies. This measurement is part of a laboratory X-ray astrophysics program utilizing the Livermore electron beam ion traps EBIT-I and EBIT-II.

Electron impact excitation cross sections have been measured for iron L-shell 3 {yields} 2 lines of FeXXI to FeXXIV at the EBIT-II electron beam ion trap using a crystal spectrometer and a 6 x 6-element array microcalorimeter. The cross sections were determined by direct normalization to the well established cross section of radiative electron capture and a summary of calculated energy dependent radiative recombination cross sections for electron capture into the ground state fine structure levels of Fe{sup 16+} to Fe{sup 23+} ions is given. The measurement results for 17 lines and their comparison with model calculations are presented. While agreement of the model calculations with experiment is good for most measured lines, significant discrepancies were found for a few lines, including the strongest line in Fe XXI.

The intensity ratios between 3 → 2 emission lines in Ni XIX were measured on the Livermore electron beam ion trap (EBIT-I) with a flat-field grating spectrometer and the NASA/Goddard Space Flight Center X-ray microcalo-rimeter. The results are consistent with earlier measurements of Fe XVII and other Ne-like ions at Livermore and confirm the problems in the atomic modeling of the direct collisional excitation for Ne-like systems.

The intensity ratios of the 3s → 2p and 3d → 2p lines in Fe XVII were measured on the Livermore electron beam ion trap employing a complementary set of spectrometers, including a high-resolution crystal spectrometer and the Goddard 32 pixel calorimeter. The resulting laboratory data are in agreement with satellite measurements of the Sun and astrophysical sources in collisional equilibrium such as Capella, Procyon, and NGC 4636. The results disagree with earlier laboratory measurements and assertions that processes not accounted for in laboratory measurements must play a role in the formation of the Fe XVII spectra in solar and astrophysical plasmas.

We report measurements of emission cross sections for iron L-shell 3 → 2 lines in Fe23+ performed on the electron beam ion trap EBIT-II using a combination of a crystal spectrometer and the spare 6 × 6 element X-Ray Spectrometer microcalorimeter from the Astro-E X-ray satellite mission. Use of the microcalorimeter enables for first time the normalization of line emission cross sections, i.e., effective electron impact excitation cross sections that include radiative cascades, to the well-established cross section of radiative electron capture, thus allowing the normalization of relative line intensity measurements using crystal spectrometers.