scholarly journals Effects of density on the oxygen ionization equilibrium in collisional plasmas

2020 ◽  
Vol 497 (2) ◽  
pp. 1443-1456
Author(s):  
R P Dufresne ◽  
G Del Zanna ◽  
N R Badnell

ABSTRACT The ion populations most frequently adopted for diagnostics in collisional plasmas are derived from the density independent coronal approximation. In higher density, lower temperature conditions, ionization rates are enhanced once metastable levels become populated, and recombination rates are suppressed if ions recombine into Rydberg levels. As a result, the formation temperatures of ions shift, altering the diagnostics of the plasma. To accurately model the effect of ionization from metastable levels, new electron impact ionization cross-sections have been calculated for oxygen, both for direct ionization and excitation–auto-ionization of the ground and metastable levels. The results have been incorporated into collisional radiative modelling to show how the ionization equilibrium of oxygen changes once metastable levels become populated. Suppression of dielectronic recombination has been estimated and also included in the modelling, demonstrating the shifts with density in comparison to the coronal approximation. The final results for the ionization equilibrium are used in differential emission measure modelling to predict line intensities for many lines emitted by O ii–O vi in the solar transition region. The predictions show improved agreement by 15–40 per cent for O ii, O vi, and the intercombination lines of O iii–O v, when compared to results from coronal approximation modelling. While there are still discrepancies with observations of these lines, this could, to a large part, be explained by variability in the observations.

2021 ◽  
Vol 16 (2) ◽  
Author(s):  
Shivani Gupta ◽  
Piyush Sinha

A theoretical model for electron impact ionization cross section has been found to be reliable for wide range of atoms is applied in this paper to the Uranium atom. A modified Kim binary encounter Bethe (BEB) method and modified Khare BEB method is employed for calculating electron impact ionization cross sections. The present results so obtained are compared with experimental as well as theoretical results known to the best of our knowledge.


2021 ◽  
Vol 75 (2) ◽  
Author(s):  
M. S. Pindzola ◽  
S. D. Loch ◽  
J. P. Colgan

Abstract Electron-impact ionization cross sections are calculated for the ground configuration of the Pb atom. Time-dependent close-coupling cross sections for the direct ionization of the 6s and 6p subshells leading to single ionization are calculated with and without a polarization potential. Configuration-average distorted-wave cross sections for the direct ionization of the 6s and 6p subshells leading to single ionization are also calculated with and without a polarization potential. We find the time-dependent close-coupling cross sections using a polarization potential to be in good agreement with convergent-close-coupling cross sections using a polarization potential. The total direct ionization cross sections are compared to two sets of experimental measurements. The differences between the direct ionization cross sections and the experimental measurements are mainly due to indirect ionization cross sections coming from the $$6s^2 6p^2 \rightarrow 6s 6p^3$$ 6 s 2 6 p 2 → 6 s 6 p 3 excitation followed by autoionization. GraphicAbstract


Atoms ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 32
Author(s):  
Michael S. Pindzola ◽  
Stuart D. Loch ◽  
James P. Colgan

The time-dependent close-coupling method has been recently applied to calculate electron-impact direct ionization cross sections for the Kr, W, and Pb atoms. An overview is presented for these three heavy neutral atom systems. When the direct ionization cross sections are combined with excitation-autoionization cross sections, the total ionization cross sections were found to be in reasonable agreement with crossed-beams measurements for Kr and Pb.


1988 ◽  
Vol 89 (7) ◽  
pp. 4035-4041 ◽  
Author(s):  
Todd R. Hayes ◽  
Randy J. Shul ◽  
Frank A. Baiocchi ◽  
Robert C. Wetzel ◽  
Robert S. Freund

Sign in / Sign up

Export Citation Format

Share Document