Research

672 KiB

Open AccessArticle

Electron Impact Excitation and Dielectronic Recombination of Highly Charged Tungsten Ions

by Zhongwen Wu, Yanbiao Fu, Xiaoyun Ma, Maijuan Li, Luyou Xie, Jun Jiang and Chenzhong Dong

Atoms 2015, 3(4), 474-494; https://doi.org/10.3390/atoms3040474 - 20 Nov 2015

Cited by 22 | Viewed by 5747

Electron impact excitation (EIE) and dielectronic recombination (DR) of tungsten ions are basic atomic processes in nuclear fusion plasmas of the International Thermonuclear Experimental Reactor (ITER) tokamak. Detailed investigation of such processes is essential for modeling and diagnosing future fusion experiments performed on [...] Read more.

Electron impact excitation (EIE) and dielectronic recombination (DR) of tungsten ions are basic atomic processes in nuclear fusion plasmas of the International Thermonuclear Experimental Reactor (ITER) tokamak. Detailed investigation of such processes is essential for modeling and diagnosing future fusion experiments performed on the ITER. In the present work, we studied total and partial electron-impact excitation (EIE) and DR cross-sections of highly charged tungsten ions by using the multiconfiguration Dirac–Fock method. The degrees of linear polarization of the subsequent X-ray emissions from unequally-populated magnetic sub-levels of these ions were estimated. It is found that the degrees of linear polarization of the same transition lines, but populated respectively by the EIE and DR processes, are very different, which makes diagnosis of the formation mechanism of X-ray emissions possible. In addition, with the help of the flexible atomic code on the basis of the relativistic configuration interaction method, DR rate coefficients of highly charged W37+ to W46+ ions are also studied, because of the importance in the ionization equilibrium of tungsten plasmas under running conditions of the ITER. Full article

(This article belongs to the Special Issue Atomic Data for Tungsten)

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894 KiB

Open AccessArticle

Detailed Analysis of Configuration Interaction and Calculation of Radiative Transition Rates in Seven Times Ionized Tungsten (W VIII)

by Jérôme Deprince and Pascal Quinet

Atoms 2015, 3(3), 299-319; https://doi.org/10.3390/atoms3030299 - 30 Jun 2015

Cited by 7 | Viewed by 4145

Abstract

A new set of oscillator strengths and transition probabilities for EUV spectral lines of seven times ionized tungsten (W VIII) is reported in the present paper. These results have been obtained using the pseudo-relativistic Hartree-Fock (HFR) method combined with a semi-empirical optimization of [...] Read more.

A new set of oscillator strengths and transition probabilities for EUV spectral lines of seven times ionized tungsten (W VIII) is reported in the present paper. These results have been obtained using the pseudo-relativistic Hartree-Fock (HFR) method combined with a semi-empirical optimization of the radial parameters minimizing the discrepancies between computed energy levels and available experimental data. The final physical model considered in the calculations has been chosen further to a detailed investigation of the configuration interaction in this atomic system characterized by complex configurations of the type 4f¹⁴5s²5p⁵, 4f¹⁴5s²5p⁴nl, 4f¹⁴5s5p⁶, 4f¹³5s²5p⁶, 4f¹³5s²5p⁵nl and 4f¹²5s²5p⁶nl (nl = 5d, 6s). Full article

(This article belongs to the Special Issue Atomic Data for Tungsten)

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1981 KiB

Open AccessArticle

Spectra of W VIII and W IX in the EUV Region

by Alexander Ryabtsev, Edward Kononov, Rimma Kildiyarova, Wan-Ü Lydia Tchang-Brillet, Jean-Francois Wyart, Norbert Champion and Christophe Blaess

Atoms 2015, 3(3), 273-298; https://doi.org/10.3390/atoms3030273 - 30 Jun 2015

Cited by 17 | Viewed by 4930

Abstract

The results obtained on the W VIII spectrum as well as on the isoelectronic spectra Lu V, Hf VI, Ta VII, and Re IX in the VUV wavelength region are summarized with emphasis on the main trends along the isoelectronic sequence. A total [...] Read more.

The results obtained on the W VIII spectrum as well as on the isoelectronic spectra Lu V, Hf VI, Ta VII, and Re IX in the VUV wavelength region are summarized with emphasis on the main trends along the isoelectronic sequence. A total of 187 lines of W VIII in the region of 160–271 Å were accurately measured and identified, 98 levels were found, and transition probabilities calculated. The isoelectronic regularities support the data on W VIII. A list of spectral lines in the region of 170–199 Å, considered as belonging to W IX, is presented. Full article

(This article belongs to the Special Issue Atomic Data for Tungsten)

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252 KiB

Open AccessArticle

Tungsten Data for Current and Future Uses in Fusion and Plasma Science

by Peter Beiersdorfer, Joel Clementson and Ulyana I. Safronova

Atoms 2015, 3(2), 260-272; https://doi.org/10.3390/atoms3020260 - 15 Jun 2015

Cited by 26 | Viewed by 6708

Abstract

We give a brief overview of our recent experimental and theoretical work involving highly charged tungsten ions in high-temperature magnetically confined plasmas. Our work includes X-ray and extreme ultraviolet spectroscopy, state-of-the-art structure calculations, the generation of dielectronic recombination rate coefficients, collisional-radiative spectral modeling [...] Read more.

We give a brief overview of our recent experimental and theoretical work involving highly charged tungsten ions in high-temperature magnetically confined plasmas. Our work includes X-ray and extreme ultraviolet spectroscopy, state-of-the-art structure calculations, the generation of dielectronic recombination rate coefficients, collisional-radiative spectral modeling and assessments of the atomic data need for X-ray diagnostics monitoring of the parameters of the core plasma of future tokamaks, such as ITER. We give examples of our recent results in these areas. Full article

(This article belongs to the Special Issue Atomic Data for Tungsten)

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548 KiB

Open AccessArticle

Tungsten Ions in Plasmas: Statistical Theory of Radiative-Collisional Processes

by Alexander V. Demura, Mikhail B. Kadomtsev, Valery S. Lisitsa and Vladimir A. Shurygin

Atoms 2015, 3(2), 162-181; https://doi.org/10.3390/atoms3020162 - 25 May 2015

Cited by 16 | Viewed by 6180

Abstract

The statistical model for calculations of the collisional-radiative processes in plasmas with tungsten impurity was developed. The electron structure of tungsten multielectron ions is considered in terms of both the Thomas-Fermi model and the Brandt-Lundquist model of collective oscillations of atomic electron density. [...] Read more.

The statistical model for calculations of the collisional-radiative processes in plasmas with tungsten impurity was developed. The electron structure of tungsten multielectron ions is considered in terms of both the Thomas-Fermi model and the Brandt-Lundquist model of collective oscillations of atomic electron density. The excitation or ionization of atomic electrons by plasma electron impacts are represented as photo-processes under the action of flux of equivalent photons introduced by E. Fermi. The total electron impact single ionization cross-sections of ions W^k⁺ with respective rates have been calculated and compared with the available experimental and modeling data (e.g., CADW). Plasma radiative losses on tungsten impurity were also calculated in a wide range of electron temperatures 1 eV–20 keV. The numerical code TFATOM was developed for calculations of radiative-collisional processes involving tungsten ions. The needed computational resources for TFATOM code are orders of magnitudes less than for the other conventional numerical codes. The transition from corona to Boltzmann limit was investigated in detail. The results of statistical approach have been tested by comparison with the vast experimental and conventional code data for a set of ions W^k⁺. It is shown that the universal statistical model accuracy for the ionization cross-sections and radiation losses is within the data scattering of significantly more complex quantum numerical codes, using different approximations for the calculation of atomic structure and the electronic cross-sections. Full article

(This article belongs to the Special Issue Atomic Data for Tungsten)

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4064 KiB

Open AccessArticle

by Alfred Müller

Atoms 2015, 3(2), 120-161; https://doi.org/10.3390/atoms3020120 - 20 May 2015

Cited by 42 | Viewed by 7055

Abstract

Collisional processes and details of atomic structure of heavy many-electron atoms and ions are not yet understood in a fully satisfying manner. Experimental studies are required for guiding new theoretical approaches. In response to fusion-related needs for collisional and spectroscopic data on tungsten [...] Read more.

Collisional processes and details of atomic structure of heavy many-electron atoms and ions are not yet understood in a fully satisfying manner. Experimental studies are required for guiding new theoretical approaches. In response to fusion-related needs for collisional and spectroscopic data on tungsten atoms in all charge states, a project has been initiated in which electron-impact and photon-induced ionization as well as photorecombination of Wq+ ions are studied. Cross sections and rate coefficients were determined for charge states q ranging from q = 1 to q = 5 for photoionization, for q = 1 up to q = 19 for electron-impact ionization and for q = 18 to q = 21 for electron-ion recombination. An overview, together with a critical assessment of the methods and results is provided. Full article

(This article belongs to the Special Issue Atomic Data for Tungsten)

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1333 KiB

Open AccessArticle

Radiative Recombination and Photoionization Data for Tungsten Ions. Electron Structure of Ions in Plasmas

by Malvina B. Trzhaskovskaya and Vladimir K. Nikulin

Atoms 2015, 3(2), 86-119; https://doi.org/10.3390/atoms3020086 - 18 May 2015

Cited by 13 | Viewed by 4883

Abstract

Theoretical studies of tungsten ions in plasmas are presented. New calculations of the radiative recombination and photoionization cross-sections, as well as radiative recombination and radiated power loss rate coefficients have been performed for 54 tungsten ions for the range W6+–W71+. The data are [...] Read more.

Theoretical studies of tungsten ions in plasmas are presented. New calculations of the radiative recombination and photoionization cross-sections, as well as radiative recombination and radiated power loss rate coefficients have been performed for 54 tungsten ions for the range W6+–W71+. The data are of importance for fusion investigations at the reactor ITER, as well as devices ASDEX Upgrade and EBIT. Calculations are fully relativistic. Electron wave functions are found by the Dirac–Fock method with proper consideration of the electron exchange. All significant multipoles of the radiative field are taken into account. The radiative recombination rates and the radiated power loss rates are determined provided the continuum electron velocity is described by the relativistic Maxwell–Jüttner distribution. The impact of the core electron polarization on the radiative recombination cross-section is estimated for the Ne-like iron ion and for highly-charged tungsten ions within an analytical approximation using the Dirac–Fock electron wave functions. The effect is shown to enhance the radiative recombination cross-sections by ≲20%. The enhancement depends on the photon energy, the principal quantum number of polarized shells and the ion charge. The influence of plasma temperature and density on the electron structure of ions in local thermodynamic equilibrium plasmas is investigated. Results for the iron and uranium ions in dense plasmas are in good agreement with previous calculations. New calculations were performed for the tungsten ion in dense plasmas on the basis of the average-atom model, as well as for the impurity tungsten ion in fusion plasmas using the non-linear self-consistent field screening model. The temperature and density dependence of the ion charge, level energies and populations are considered. Full article

(This article belongs to the Special Issue Atomic Data for Tungsten)

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255 KiB

Open AccessArticle

Collisional-Radiative Modeling of Tungsten at Temperatures of 1200–2400 eV

by James Colgan, Christopher J. Fontes, Honglin Zhang and Joseph Abdallah, Jr.

Atoms 2015, 3(2), 76-85; https://doi.org/10.3390/atoms3020076 - 30 Apr 2015

Cited by 8 | Viewed by 4713

Abstract

We discuss new collisional-radiative modeling calculations of tungsten at moderate temperatures of 1200 to 2400 eV. Such plasma conditions are relevant to ongoing experimental work at ASDEX Upgrade and are expected to be relevant for ITER. Our calculations are made using the Los [...] Read more.

We discuss new collisional-radiative modeling calculations of tungsten at moderate temperatures of 1200 to 2400 eV. Such plasma conditions are relevant to ongoing experimental work at ASDEX Upgrade and are expected to be relevant for ITER. Our calculations are made using the Los Alamos National Laboratory (LANL) collisional-radiative modeling ATOMIC code. These calculations formed part of a submission to the recent NLTE-8 workshop that was held in November 2013. This series of workshops provides a forum for detailed comparison of plasma and spectral quantities from NLTE collisional-radiative modeling codes. We focus on the LANL ATOMIC calculations for tungsten that were submitted to the NLTE-8 workshop and discuss different models that were constructed to predict the tungsten emission. In particular, we discuss comparisons between semi-relativistic configuration-average and fully relativistic configuration-average calculations. We also present semi-relativistic calculations that include fine-structure detail, and discuss the difficult problem of ensuring completeness with respect to the number of configurations included in a CR calculation. Full article

(This article belongs to the Special Issue Atomic Data for Tungsten)

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1186 KiB

Open AccessArticle

Fully Relativistic Electron Impact Excitation Cross-Section and Polarization for Tungsten Ions

by Priti, Dipti, Lalita Sharma and Rajesh Srivastava

Atoms 2015, 3(2), 53-75; https://doi.org/10.3390/atoms3020053 - 28 Apr 2015

Cited by 7 | Viewed by 4880

Abstract

Electron impact excitation of highly charged tungsten ions in the framework of a fully relativistic distorted wave approach is considered in this paper. Calculations of electron impact excitation cross-sections for the M- and L-shell transitions in the tungsten ions Wⁿ⁺ (n [...] Read more.

Electron impact excitation of highly charged tungsten ions in the framework of a fully relativistic distorted wave approach is considered in this paper. Calculations of electron impact excitation cross-sections for the M- and L-shell transitions in the tungsten ions Wⁿ⁺ (n = 44–66) and polarization of the decay of photons from the excited tungsten ions are briefly reviewed and discussed. New calculations in the wide range of incident electron energies are presented for M-shell transitions in the K-like through Ne-like tungsten ions. Full article

(This article belongs to the Special Issue Atomic Data for Tungsten)

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410 KiB

Open AccessArticle

Ab-Initio Calculations of Level Energies, Oscillator Strengths and Radiative Rates for E1 Transitions in Beryllium-Like Iron

by Ahmed Abou El-Maaref, Stefan Schippers and Alfred Müller

Atoms 2015, 3(1), 2-52; https://doi.org/10.3390/atoms3010002 - 20 Jan 2015

Cited by 7 | Viewed by 4874

Abstract

In the present work, energy levels, oscillator strengths, radiative rates and wavelengths of Be-like iron (Fe\(^{22+}\)) from ab-initio calculations using the multiconfiguration Dirac-Hartree-Fock method are presented. These quantities have been calculated for a set of configurations in the general form \(1s^2\,nl\,n'l'\) where [...] Read more.

In the present work, energy levels, oscillator strengths, radiative rates and wavelengths of Be-like iron (Fe\(^{22+}\)) from ab-initio calculations using the multiconfiguration Dirac-Hartree-Fock method are presented. These quantities have been calculated for a set of configurations in the general form \(1s^2\,nl\,n'l'\) where \(n=2,3\) and \(\,n'=2,3,4,5\) and \(l=s,p,d\) and \(\,l'=s, p, d, f, g\). In addition, excitations of up to four electrons, including core-electron excitations, have been considered to improve the quality of the wave functions. This study comprises an extensive set of E1 transition rates between states with different \(J\). The present results are compared with the available experimental and theoretical data. Full article

(This article belongs to the Special Issue Atomic Data for Tungsten)

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