Comprehensive Laboratory Benchmark of K-shell Dielectronic Satellites of Fe xxv–xxi Ions

We report on comprehensive laboratory studies of the K-shell dielectronic recombination resonances of Fe xxv-xxi ions that prominently contribute to the hard X-ray spectrum of hot astrophysical plasmas. By scanning a monoenergetic electron beam to resonantly excite trapped Fe ions in an electron beam ion trap and achieving a high electron-ion collision energy resolution of ∼7 eV, we resolve their respective KLn satellites up to n ′ = 11 . By normalization to known radiative recombination cross sections, we also determine their excitation cross sections and that of the continuum with uncertainties below 15% and verify our results with an independent normalization based on previous measurements. Our experimental data excellently confirm the accuracy and suitability of distorted-wave calculations obtained with the Flexible Atomic Code for modeling astrophysical and fusion plasmas.

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Research was funded by the Max-Planck-Gesselschaft (MPG), Germany. C.S. acknowledges support from MPG and NASA-JHU Cooperative Agreement. M.F.G. acknowledges support by NASA under APRA grant 80NSSC 20K0835. M.A.L. and F.S.P. acknowledge support from the NASA Astrophysics Program. © 2025. The Author(s). Published by the American Astronomical Society.