Electron impact excitation for He-like ions with Z = 20–42⋆
1 Division of Mathematical Physics, Department of PhysicsLund University, Box 118, 221 00 Lund, Sweden
2 Shanghai EBIT Lab, Institute of Modern Physics, Department of Nuclear Science and Technology, Fudan University, 200433 Shanghai, PR China
3 Institute of Applied Physics and Computational Mathematics, 100088 Beijing, PR China
4 Hebei Key Lab of Optic-electronic Information and Materials, The College of Physics Science and Technology, Hebei University, 071002 Baoding, PR China
5 Department of Radiotherapy, Shanghai Changhai Hospital, Second Military Medical University, 200433 Shanghai, PR China
6 College of Science, National University of Defense Technology, 410073 Changsha, PR China
Received: 8 November 2016
Accepted: 8 January 2017
Aims. Spectral lines of He-like ions are among the most prominent features in X-ray spectra from a large variety of astrophysical and high-temperature fusion plasmas. A reliable plasma modeling and interpretation of the spectra require a large amount of accurate atomic data related to various physical processes. In this paper, we focus on the electron-impact excitation (EIE) process.
Methods. We adopted the independent process and isolated resonances approximation using distorted waves (IPIRDW). Resonant stabilizing transitions and decays to lower-lying autoionizing levels from the resonances are included as radiative damping. To verify the applicability of the IPIRDW approximation, an independent Dirac R-matrix calculation was also performed. The two sets of results show excellent agreement.
Results. We report electron impact excitation collision strengths for transitions among the lowest 49 levels of the 1snl(n ≤ 5,l ≤ (n−1)) configurations in He-like ions with 20 ≤ Z ≤ 42. The line ratios R and G are calculated for Fe XXV and Kr XXXV.
Conclusions. Compared to previous theoretical calculations, our IPIRDW calculation treats resonance excitation and radiative damping effects more comprehensively, and the resulting line emission cross sections show good agreement with the experimental observations. Our results should facilitate the modeling and diagnostics of various astrophysical and laboratory plasmas.
Key words: atomic data / atomic processes
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