Laboratory benchmarks for collisional excitation cross sections of K-shell transitions in Fe group elements
Abstract
Electron impact excitation (EIE) is the dominant line formation process in collisional plasmas. Accurate EIE cross sections are therefore crucial for, for example, temperature sensitive line ratios and for accurate predictions of expected line strengths as a probe for "missing" flux from resonant scattering. K-shell transitions in Fe-group elements provide important diagnostics in energetic, collisional sources such as supernova remnants and clusters of galaxies. As shown by observations with Hitomi-SXS, their diagnostic potential will increase even further with upcoming X-ray missions providing high spectral resolution in the Fe K band such as XRISM and Athena.Using the Lawrence Livermore National Laboratory's electron beam ion trap EBIT-I and the NASA/GSFC EBIT Calorimeter Spectrometer (ECS) we measure the absolute X-ray emission cross sections of K-shell transitions in highly charged ions of Fe-group elements. The excitation cross sections are brought to an absolute scale by normalizing the observed flux of the directly excited lines to the simultaneously measured emission lines from radiative recombination, whose cross sections are well known. The measured cross sections are then used to benchmark theoretical cross sections.This work was supported by LLNL under Contract DE-AC52-07NA27344 and by NASA grants to LLNL and NASA/GSFC.
- Publication:
-
AAS/High Energy Astrophysics Division
- Pub Date:
- March 2019
- Bibcode:
- 2019HEAD...1720303H