R-matrix calculations for electron impact excitation and modelling application for coronal plasmas

G Y Liang(1,2), N R Badnell(1), G Del Zanna(3), H E Mason(3), P J Storey(4), and G Zhao(2)

(1)Department of Physics, University of Strathclyde, Glasgow, G4 0NG, UK. (2)National Astronomical Observatories, CAS, Beijing, 100012, China. (3)DAMTP, Centre for Mathematical Sciences, Cambridge, CB3 0WA, UK. (4)Department of Physics and Astronomy, University College London, London, WC1E 6BT, UK.

A large number of high-resolution and high-quality spectra have been and will be obtained in recent/coming years from both the EUV (e.g. Hinode) and X-ray (e.g. Chandra, IXO) regions. Many emission lines observed in these spectra are potential diagnostics of the Te/nof coronal-like hot plasmas. That will pose insights on the heating mechanism and coronal structure. Such diagnostics and associated line identifications require accurate atomic data.

The R-matrix approach is generally regarded as a more accurate approximation than the distorted wave method for the electron-ion interaction process in a hot plasma due to its ability to efficiently include resonances. To date, several R-matrix based approaches have been established, e.g. Breit-Pauli (BP) [1], fully relativistic Dirac (DARC) [2] and the ICFT [3] approach.

The ICFT method is less-time demanding when compared to the Breit-Pauli and DARC R-matrix codes because it considers an LS-coupled Hamiltonian. However, the ICFT method eliminates at root the deficiency of previous LS-based methods (e.g. JAJOM) via the use of multi-channel quantum defect theory (MQDT). The current ICFT code suite has been parallelized and has been shown to be highly robust. Hence, it is now feasible to provide excitation data for iso-electronic sequences within the R-matrix framework, which is one of the goals of the UK Atomic Processes for Astrophysical Plasmas (APAP) network.

So far, the R-matrix calculations for He-like, Li-like, F-like, Ne-like and Na-like iso-electronic sequences [4] have been completed and resultant data were assessed to be reliable. Calculations for another three iso-electronic sequence (including Be-like, B-like and Mg-like) and urgently important ions (e.g. S6+…S11+) are planned in the 2nd APAP program. These data are routinely used by several modelling codes, e.g. CHIANTI, ADAS, APED, etc.

Modelling and diagnostic applications of resultant excitation data help to clarify those unknown emissions [5], resolve blending contributions, and understand the conditions of emitters or absorbers, e.g. the soft X-ray and EUV spectroscopy of Fe13+ in stellar coronae and laboratory ‘corona’ produced in electron beam ion traps [6].

In summary, the APAP Project will generate an extensive set of reliable excitation data utilizing the ICFT R-matrix method. This will update much of the distorted wave data presently used by the astrophysical community and its use may overcome some shortcomings in the present astrophysical modelling. The work is also of importance to fusion modelling and diagnostics.

Poster presented at the 17th International Conference on Atomic Processes in Plasmas, Queen’s University Belfast, 19-22 July 2011.

References

  1. K.A. Berrington W. Eissner, and P.N. Norrington, Comput. Phys. Commun. 92, 290 (1995).
  2. P.H. Norrington, and I.P. Grant, J. Phys. B: At. Mol. Opt. Phys. 20, 4869 (1987).
  3. F. Robicheaux et al, Phys. Rev. A 52, 1319 (1995).
  4. G.Y. Liang, and N.R. Badnell, Astron. Astrophys. 528, A69 (2011).
  5. G.Y. Liang, and G. Zhao, Mon. Not. R. Astron. Soc. 405, 1987 (2010).
  6. G.Y. Liang at al, Astrophys. J. Supp. Ser. 190, 322 (2010).
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