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3 pages, 178 KiB

Open AccessEditorial

Spectral Line Shapes in Plasmas II

by Evgeny Stambulchik, Annette Calisti, Hyun-Kyung Chung and Manuel Á. González

Atoms 2019, 7(1), 20; https://doi.org/10.3390/atoms7010020 - 6 Feb 2019

Cited by 5 | Viewed by 2458

Abstract

The Spectral Line Shapes in Plasmas (SLSP) code comparison workshop series [...] Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

Research

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12 pages, 2515 KiB

Open AccessFeature PaperArticle

A New Procedure to Determine the Plasma Parameters from a Genetic Algorithm Coupled with the Spectral Line-Shape Code PPP

by Caroline Mossé, Paul Génésio, Nelly Bonifaci and Annette Calisti

Atoms 2018, 6(4), 55; https://doi.org/10.3390/atoms6040055 - 26 Sep 2018

Cited by 3 | Viewed by 3630

Abstract

A method of analysis of experimental spectra for obtaining the plasma parameters is presented and discussed. Based on the coupling of the spectral line-shape code PPP with the genetic algorithm PIKAIA, the proposed method is inspired by natural selection mechanisms resulting in the [...] Read more.

A method of analysis of experimental spectra for obtaining the plasma parameters is presented and discussed. Based on the coupling of the spectral line-shape code PPP with the genetic algorithm PIKAIA, the proposed method is inspired by natural selection mechanisms resulting in the development of basic genetic operators. The spectra analysis is performed by fitting experimental spectra with synthetic spectral line profiles obtained by using theoretical models and a set of plasma parameters, such as its temperature and electron density. In the present paper, the diagnostic procedure based on a genetic algorithm coupled with the PPP code has been used for the analysis of both hydrogen Balmer-β and He I 492.2 nm lines in the helium plasma created by corona discharge. The broadening of these spectral lines due to the Stark effect has been considered, together with the van der Waals and instrumental broadening. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

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14 pages, 439 KiB

Open AccessFeature PaperArticle

The Third and Fourth Workshops on Spectral Line Shapes in Plasma Code Comparison: Isolated Lines

by Sylvie Sahal-Bréchot, Evgeny Stambulchik, Milan S. Dimitrijević, Spiros Alexiou, Bin Duan and Véronique Bommier

Atoms 2018, 6(2), 30; https://doi.org/10.3390/atoms6020030 - 31 May 2018

Cited by 8 | Viewed by 2937

Abstract

The purpose of the Spectral Line Shapes in Plasmas (SLSP) code comparison workshop is to compare different computational and analytical methods, in order to pinpoint sources of disagreements, infer limits of applicability, and assess accuracy. The present paper reviews a part of the [...] Read more.

The purpose of the Spectral Line Shapes in Plasmas (SLSP) code comparison workshop is to compare different computational and analytical methods, in order to pinpoint sources of disagreements, infer limits of applicability, and assess accuracy. The present paper reviews a part of the results of the third (2015) and fourth (2017) workshops related to isolated lines. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

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14 pages, 34974 KiB

Open AccessFeature PaperArticle

H-β Line in a Corona Helium Plasma: A Multi-Code Line Shape Comparison

by Roshin Raj Sheeba, Mohammed Koubiti, Nelly Bonifaci, Franck Gilleron, Caroline Mossé, Jean-Christophe Pain, Joël Rosato and Evgeny Stambulchik

Atoms 2018, 6(2), 29; https://doi.org/10.3390/atoms6020029 - 23 May 2018

Cited by 4 | Viewed by 3615

Abstract

Many spectroscopic diagnostics are routinely used as techniques to infer the plasma parameters from line emission spectra, but their accuracy depends on the numerical model or code used for the fitting process. However, the validation of a line shape code requires some steps: [...] Read more.

Many spectroscopic diagnostics are routinely used as techniques to infer the plasma parameters from line emission spectra, but their accuracy depends on the numerical model or code used for the fitting process. However, the validation of a line shape code requires some steps: the comparison of the line shape code with other similar codes for some academic (simple) cases and then for more complex ones, the comparison of the fitting parameters obtained from the best fit of the experimental spectra with those obtained with other diagnostic techniques, and/or the comparison of the fitting parameters obtained by different codes to fit the same experimental data. Here we compare the profiles of the hydrogen Balmer β line in helium plasma computed by five codes for a selected set of plasma parameters and we report on the plasma parameters inferred by each of them from the fitting to a number of experimental spectra measured in a helium corona discharge where the pressure was in the range of 1–5 bars. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

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12 pages, 1554 KiB

Open AccessFeature PaperArticle

Revisiting the Stark Width and Shift of He II Pα

by Christine Stollberg, Evgeny Stambulchik, Bin Duan, Marco A. Gigosos, Diego González Herrero, Carlos A. Iglesias and Caroline Mossé

Atoms 2018, 6(2), 23; https://doi.org/10.3390/atoms6020023 - 24 Apr 2018

Cited by 6 | Viewed by 3356

Abstract

We report experimental determination of plasma-induced Stark widths and shifts of the He II P

α

line and a comparison of the results with calculations performed by several computational approaches. The measurements were carried out in a small compressing plasma channel device, reaching [...] Read more.

We report experimental determination of plasma-induced Stark widths and shifts of the He II P

α

line and a comparison of the results with calculations performed by several computational approaches. The measurements were carried out in a small compressing plasma channel device, reaching electron densities in excess of

10^{18} {cm}^{- 3}

and temperatures of a few eV. The experimental data are in a good agreement with some previously published studies. However, the measured relation between the Stark shift and width could not be reproduced by either of the codes, and this disagreement is not yet resolved. This suggests the existence of an additional effect that is not accounted for in the present models and leads to a larger than expected Stark shift of the He II P

α

line. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

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13 pages, 398 KiB

Open AccessFeature PaperArticle

Matrix Methods for Solving Hartree-Fock Equations in Atomic Structure Calculations and Line Broadening

by Thomas Gomez, Taisuke Nagayama, Chris Fontes, Dave Kilcrease, Stephanie Hansen, Mike Montgomery and Don Winget

Atoms 2018, 6(2), 22; https://doi.org/10.3390/atoms6020022 - 23 Apr 2018

Cited by 7 | Viewed by 4528

Abstract

Atomic structure of N-electron atoms is often determined by solving the Hartree-Fock equations, which are a set of integro-differential equations. The integral part of the Hartree-Fock equations treats electron exchange, but the Hartree-Fock equations are not often treated as an integro-differential equation. The [...] Read more.

Atomic structure of N-electron atoms is often determined by solving the Hartree-Fock equations, which are a set of integro-differential equations. The integral part of the Hartree-Fock equations treats electron exchange, but the Hartree-Fock equations are not often treated as an integro-differential equation. The exchange term is often approximated as an inhomogeneous or an effective potential so that the Hartree-Fock equations become a set of ordinary differential equations (which can be solved using the usual shooting methods). Because the Hartree-Fock equations are an iterative-refinement method, the inhomogeneous term relies on the previous guess of the wavefunction. In addition, there are numerical complications associated with solving inhomogeneous differential equations. This work uses matrix methods to solve the Hartree-Fock equations as an integro-differential equation. It is well known that a derivative operator can be expressed as a matrix made of finite-difference coefficients; energy eigenvalues and eigenvectors can be obtained by using linear-algebra packages. The integral (exchange) part of the Hartree-Fock equation can be approximated as a sum and written as a matrix. The Hartree-Fock equations can be solved as a matrix that is the sum of the differential and integral matrices. We compare calculations using this method against experiment and standard atomic structure calculations. This matrix method can also be used to solve for free-electron wavefunctions, thus improving how the atoms and free electrons interact. This technique is important for spectral line broadening in two ways: it improves the atomic structure calculations, and it improves the motion of the plasma electrons that collide with the atom. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

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11 pages, 36749 KiB

Open AccessFeature PaperArticle

Broadening of the Neutral Helium 492 nm Line in a Corona Discharge: Code Comparisons and Data Fitting

by Roshin Raj Sheeba, Mohammed Koubiti, Nelly Bonifaci, Franck Gilleron, Jean-Christophe Pain and Evgeny Stambulchik

Atoms 2018, 6(2), 19; https://doi.org/10.3390/atoms6020019 - 16 Apr 2018

Cited by 4 | Viewed by 4055

Abstract

Passive plasma spectroscopy is a well-established non-intrusive diagnostic technique. Depending on the emitter and its environment which determine the dominant interactions and effects governing emission line shapes, passive spectroscopy allows the determination of electron densities, emitter and perturber temperatures, as well as other [...] Read more.

Passive plasma spectroscopy is a well-established non-intrusive diagnostic technique. Depending on the emitter and its environment which determine the dominant interactions and effects governing emission line shapes, passive spectroscopy allows the determination of electron densities, emitter and perturber temperatures, as well as other quantities like relative abundances. However, using spectroscopy requires appropriate line shape codes retaining all the physical effects governing the emission line profiles. This is required for line shape code developers to continuously correct or improve them to increase their accuracy when applied for diagnostics. This is exactly the aim expected from code–code and code–data comparisons. In this context, the He i 492 nm line emitted in a helium corona discharge at room temperature represents an ideal case since its profile results from several broadening mechanisms: Stark, Doppler, resonance, and van der Waals. The importance of each broadening mechanism depends on the plasma parameters. Here the profiles of the He i 492 nm in a helium plasma computed by various codes are compared for a selected set of plasma parameters. In addition, preliminary results related to plasma parameter determination using an experimental spectrum from a helium corona discharge at atmospheric pressure, are presented. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

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8 pages, 305 KiB

Open AccessFeature PaperArticle

Stark Broadening of Cr III Spectral Lines: DO White Dwarfs

by Milan S. Dimitrijević and Abhishek Chougule

Atoms 2018, 6(2), 15; https://doi.org/10.3390/atoms6020015 - 3 Apr 2018

Cited by 11 | Viewed by 4042

Abstract

Using the modified semiempirical method of Dimitrijević and Konjević, Stark widths have been calculated for six Cr III transitions, for an electron density of 10

^{17}

cm

^{‒ 3}

and for temperatures from 5000–80,000 K. Results have been used for the investigation of [...] Read more.

Using the modified semiempirical method of Dimitrijević and Konjević, Stark widths have been calculated for six Cr III transitions, for an electron density of 10

^{17}

cm

^{‒ 3}

and for temperatures from 5000–80,000 K. Results have been used for the investigation of the influence of Stark broadening on spectral lines in cool DO white dwarf atmospheres. Calculated Stark widths will be implemented in the STARK-B database, which is also a part of the Virtual Atomic and Molecular Data Center (VAMDC). Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

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26 pages, 1940 KiB

Open AccessFeature PaperArticle

The Fourth Workshop on Lineshape Code Comparison: Line Merging

by Spiros Alexiou, Evgeny Stambulchik, Thomas Gomez and Mohammed Koubiti

Atoms 2018, 6(2), 13; https://doi.org/10.3390/atoms6020013 - 31 Mar 2018

Cited by 8 | Viewed by 4191

Abstract

For a given set of plasma parameters, along a single series (Lyman, Balmer, etc.) the lines with higher principal quantum number (n) lines get progressively wider, closer to each other, and start merging for a certain critical n. In the [...] Read more.

For a given set of plasma parameters, along a single series (Lyman, Balmer, etc.) the lines with higher principal quantum number (n) lines get progressively wider, closer to each other, and start merging for a certain critical n. In the present work, four different codes (with further options) are used to calculate the entire Balmer series for moderate and high electron densities. Particular attention is paid to the relevant physics, such as the cutoff criteria, strong and penetrating electron collisions. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

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4 pages, 357 KiB

Open AccessFeature PaperArticle

Influence of Helical Trajectories of Perturbers on Stark Line Shapes in Magnetized Plasmas

by J. Rosato, S. Ferri and R. Stamm

Atoms 2018, 6(1), 12; https://doi.org/10.3390/atoms6010012 - 13 Mar 2018

Cited by 12 | Viewed by 3114

Abstract

In plasmas subject to a strong magnetic field, the dynamical properties of the microfield are affected by the cyclotron motion, which can alter Stark-broadened lines. We illustrate this effect through calculations of the hydrogen Lyman

α

line in an ideal one-component plasma. A [...] Read more.

In plasmas subject to a strong magnetic field, the dynamical properties of the microfield are affected by the cyclotron motion, which can alter Stark-broadened lines. We illustrate this effect through calculations of the hydrogen Lyman

α

line in an ideal one-component plasma. A focus is put on the central Zeeman component. It is shown that the atomic dipole autocorrelation function decreases more slowly if the cyclotron motion is retained. In the frequency domain, this denotes a reduction of the line broadening. A discussion based on numerical simulations and analytical estimates is done. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

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20 pages, 882 KiB

Open AccessFeature PaperArticle

ZEST: A Fast Code for Simulating Zeeman-Stark Line-Shape Functions

by Franck Gilleron and Jean-Christophe Pain

Atoms 2018, 6(1), 11; https://doi.org/10.3390/atoms6010011 - 12 Mar 2018

Cited by 5 | Viewed by 4374

Abstract

We present the ZEST code, dedicated to the calculation of line shapes broadened by Zeeman and Stark effects. As concerns the Stark effect, the model is based on the Standard Lineshape Theory in which ions are treated in the quasi-static approximation, whereas the [...] Read more.

We present the ZEST code, dedicated to the calculation of line shapes broadened by Zeeman and Stark effects. As concerns the Stark effect, the model is based on the Standard Lineshape Theory in which ions are treated in the quasi-static approximation, whereas the effects of electrons are represented by weak collisions in the framework of a binary collision relaxation theory. A static magnetic field may be taken into account in the radiator Hamiltonian in the dipole approximation, which leads to additional Zeeman splitting patterns. Ion dynamics effects are implemented using the fast Frequency-Fluctuation Model. For fast calculations, the static ion microfield distribution in the plasma is evaluated using analytic fits of Monte-Carlo simulations, which depend only on the ion-ion coupling parameter and the electron-ion screening factor. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

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Review

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28 pages, 1542 KiB

Open AccessFeature PaperReview

Beyond the Linear Stark Effect: A Retrospective

by Alexander V. Demura

Atoms 2018, 6(2), 33; https://doi.org/10.3390/atoms6020033 - 6 Jun 2018

Cited by 16 | Viewed by 3837

Abstract

A review of studies of the electric-field influence on spectral lines is presented, beginning from the discovery of the Stark effect, and in particular focused on phenomena related to the effects of the plasma microfield non-uniformity. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

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