Electron impact excitation cross section measurement for n=3 to n=2 line emission in Fe17+ to Fe23+

We report the measurement of electron impact excitation cross sections for the strong iron L-shell 3 ! 2 lines of Fe XVIII through Fe XXIV at the EBIT-I electron beam ion trap using a crystal spectrometer and a 6 x 6 pixel array microcalorimeter. The cross sections were determined by direct normalization to the well established theoretical cross section of radiative electron capture through a sophisticated model analysis, which results in the excitation cross section for 48 lines at multiple electron energies. We also studied the electron-density-dependent nature of the emission lines, which is demonstrated by the effective excitation cross section of the 3d -> 2p transition in Fe XXI.