Benchmarking Model Calculations of Fe XVII Dielectronic Recombination Satellite Line Cross Sections Using an Electron Beam Ion Trap

Dielectronic recombination (DR) is the dominant photorecombination channel for Fe XVII in hot astrophysical plasmas, producing strong satellite transitions seen in the 3s-2p and 3d-2p line formation channels of X-ray spectra from stellar coronae. Dielectronic resonances also contribute strongly to the collisional excitation of Fe XVII ions. Theoretical calculations of DR, resonant excitation (RE), and direct excitation (DE) are effectively benchmarked by EBIT studies in which the electron beam energy is swept over the energy range of the resonances. Accurate interpretations of these DR channels are essential for accurate astrophysical plasma diagnostics. We continue the work of Shah et al. (2019) and Grilo et al. (2021) by using the Flexible Atomic Code to calculate cross sections for the DR satellite lines of Fe XVII, with configurations including principal quantum numbers and orbital angular momentum quantum numbers up to n ≤ 100 and l ≤ 8 respectively. We benchmarked our theoretical predictions by converting the line emissivities to absolute cross sections, and compared these cross sections in all orders to experimental cross sections of Fe XVII resonances that were mono-energetically excited in FLASH-EBIT at MPI-K in Heidelberg, Germany. In particular, we extended the experimental benchmark to all observable DR and DE channels, specifically the n=4-2 DR resonances of Fe XVII. Our theoretical calculations show a 20-25% overestimation of the n=4 DR and DE absolute cross sections, but accurate overall agreement when broadening the cross sections with a Gaussian function to match the photon energy resolution of the FLASH-EBIT silicon drift detector.