Scaling of collision strengths for highly-excited states of ions of the H- and He-like sequences

L. Fernández-Menchero, G. Del Zanna, N. R. Badnell

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)
36 Downloads (Pure)

Abstract

Emission lines from highly-excited states (n ≥ 5) of H- and He-like ions have been detected in astrophysical sources and fusion plasmas. For such excited states, R-matrix or distorted wave calculations for electron-impact excitation are very limited, due to the large size of the atomic basis set needed to describe them. Calculations for n ≥ 6 are also not generally available. We study the behaviour of the electron-impact excitation collision strengths and effective collision strengths for the most important transitions used to model electron collision dominated astrophysical plasmas, solar, for example. We investigate the dependence on the relevant parameters: the principal quantum number n or the nuclear charge Z. We also estimate the importance of coupling to highly-excited states and the continuum by comparing the results of different sized calculations. We provide analytic formulae to calculate the electron-impact excitation collision strengths and effective collision strengths to highly-excited states (n ≥ 8) of H- and He-like ions. These extrapolated effective collision strengths can be used to interpret astrophysical and fusion plasma via collisional-radiative modelling.
Original languageEnglish
Article numberA135
Number of pages9
JournalAstronomy and Astrophysics
Volume592
Early online date15 Aug 2016
DOIs
Publication statusPublished - 31 Aug 2016

Keywords

  • atomic data
  • sun
  • corona
  • spectroscopy
  • emission lines
  • astrophysical sources
  • fusion plasmas
  • electron-impact excitation
  • collision strengths
  • principal quantum number
  • nuclear charge
  • collisional-radiative modelling

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