Electron-impact Multiple-ionization Cross Sections for Atoms and Ions of Helium through Zinc

Hahn, Michael; Müller, A.; Savin, D. W.

doi:10.3847/1538-4357/aa9276

Cited by 26 publications

(26 citation statements)

References 98 publications

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“…The main DI process occurs via neighboring ionisation stages, however double ionisation processes can sometimes be non-negligible, as e.g., shown by Hahn et al. (2017). More details and references about these processes can be found below in the atomic data section.…”

Section: The Formation Of the Xuv Spectrummentioning

confidence: 96%

Solar UV and X-ray spectral diagnostics

Zanna

Mason

2018

Living Rev Sol Phys

222

139

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X-ray and ultraviolet (UV) observations of the outer solar atmosphere have been used for many decades to measure the fundamental parameters of the solar plasma. This review focuses on the optically thin emission from the solar atmosphere, mostly found at UV and X-ray (XUV) wavelengths, and discusses some of the diagnostic methods that have been used to measure electron densities, electron temperatures, differential emission measure (DEM), and relative chemical abundances. We mainly focus on methods and results obtained from high-resolution spectroscopy, rather than broad-band imaging. However, we note that the best results are often obtained by combining imaging and spectroscopic observations. We also mainly focus the review on measurements of electron densities and temperatures obtained from single ion diagnostics, to avoid issues related to the ionisation state of the plasma. We start the review with a short historical introduction on the main XUV high-resolution spectrometers, then review the basics of optically thin emission and the main processes that affect the formation of a spectral line. We mainly discuss plasma in equilibrium, but briefly mention non-equilibrium ionisation and non-thermal electron distributions. We also summarise the status of atomic data, which are an essential part of the diagnostic process. We then review the methods used to measure electron densities, electron temperatures, the DEM, and relative chemical abundances, and the results obtained for the lower solar atmosphere (within a fraction of the solar radii), for coronal holes, the quiet Sun, active regions and flares.

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Section: The Formation Of the Xuv Spectrummentioning

confidence: 96%

Solar UV and X-ray spectral diagnostics

Zanna

Mason

2018

Living Rev Sol Phys

222

139

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“…Hahn et al (2017) compiled a set of experimental, multipleionisation cross-sections for a wide range of astrophysically relevant ions. From these, they provided geometrical fitting formulae to reproduce the cross-sections.…”

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confidence: 99%

Modelling ion populations in astrophysical plasmas: carbon in the solar transition region

Dufresne

Zanna

2019

A&A

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The aim of this work is to improve the modelling of ion populations in higher density, lower temperature astrophysical plasmas, of the type commonly found in lower solar and stellar atmospheres. Ion population models for these regions frequently employ the coronal approximation, which assumes conditions more suitable to the upper solar atmosphere, where high temperatures and lower densities prevail. These assumptions include all ion charge-states being in the ground state, and steady-state equilibrium where there is sufficient time for ionisation and recombination to take place. Using the coronal approximation for modelling the solar transition region gives theoretical lines intensities for the Li-like and Na-like isoelectronic sequences which can be factors of 2-5 times lower than observed. The works of Burgess & Summers (1969) and Nussbaumer & Storey (1975) showed the important part ions in excited levels play when included in the modelling. As density increases metastable levels become populated and ionisation rates increase, whereas dielectronic recombination through the highly-excited levels becomes suppressed. Photo-ionisation was also shown by Nussbaumer & Storey to have an effect on the charge-state distribution of carbon in these regions. Their models, however, used approximations for the atomic rates to determine the ion balance. Presented here is the first stage in updating these earlier models of carbon by using rates from up-to-date atomic calculations and more recent photo-ionising radiances for the quiet Sun. Where such atomic rates are not readily available, in the case of electron-impact direct ionisation and excitation-auto-ionisation, new calculations have been made using the Flexible Atomic Code and Autostructure, and compared to theoretical and experimental studies. The effects each atomic process has on the ion populations as density changes is demonstrated, and final results from the modelling are compared to the earlier works. Lastly, the new results for ion populations are used to predict line intensities for the solar transition region in the quiet Sun, and these are compared with predictions from coronal-approximation modelling and with observations. Significant improvements in the predicted line intensities are seen in comparison to those obtained from zero-density modelling of carbon.

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“…in unit of 10 -20 cm 2 . 𝜎 Regarding the variation of the cross sections with z, it is clear that for the three levels 1 1 S, 2 1 S and 2 3 S the maximum values of the cross sections are inversely proportional to the values of z for the three helium like ions, as also indicated by the shapes of the figures 1, 2 and 3. The maximum values for the cross-sections of (22.08, 11.18, 6.27) x 10 -20 cm 2 have been calculated successively for the three ions C V, N VI and O VII for the ground state 1 1 S. For the 2 1 S level the values are successively (187.57, 83.89, 53.47 ) x 10 -20 cm 2 , whereas for the level 2 3 S the maximum cross sections take successively the values (174.14, 90.71, 50.71) x 10 -20 cm 2 .…”

Section:  X10mentioning

confidence: 75%

“…Electron impact ionization (EII) of atoms and molecules was studied during the last hundred years, from the very early days of modern physics [1]. The cross sections and ionization rates are atomic data that have important applications in astrophysics and plasma physics [2,3]. Several research works have been carried out in the calculation of ionization cross section using different methods [4], including classical methods [5], Coulomb Born approximation [6] and semi-empirical equations [7].…”

Section: Introductionmentioning

confidence: 99%

Ionization cross section by electron impact of helium-like ions

2021

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In this paper we present our calculation of the cross section ionization by electron impact of C V, N VI and O VII. Using the Flexible Atomic Code (FAC), we obtain the cross sections for the ionization of these ions from the ground state 11S, and from the unstable states 21S and 23S. Our results are in good agreement with those based on the Coulomb Born (CB) approximation and the available measurements.

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Electron-impact Multiple-ionization Cross Sections for Atoms and Ions of Helium through Zinc

Cited by 26 publications

References 98 publications

Solar UV and X-ray spectral diagnostics

Solar UV and X-ray spectral diagnostics

Modelling ion populations in astrophysical plasmas: carbon in the solar transition region

Ionization cross section by electron impact of helium-like ions

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