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Atoms, Volume 5, Issue 4 (December 2017)

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Research

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Open AccessFeature PaperArticle Effect of Turbulence on Line Shapes in Astrophysical and Fusion Plasmas
Atoms 2017, 5(4), 34; doi:10.3390/atoms5040034
Received: 30 August 2017 / Revised: 15 September 2017 / Accepted: 18 September 2017 / Published: 25 September 2017
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Abstract
We look at the effect of wave collapse turbulence on a hydrogen line shape in plasma. An atom immersed in plasma affected by strong Langmuir turbulence may be perturbed by a sequence of wave packets with a maximum electric field magnitude that is
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We look at the effect of wave collapse turbulence on a hydrogen line shape in plasma. An atom immersed in plasma affected by strong Langmuir turbulence may be perturbed by a sequence of wave packets with a maximum electric field magnitude that is larger than the Holtsmark field. For such conditions, we propose to calculate the shape of the hydrogen Lyman α Lyman β and Balmer α lines with a numerical integration of the Schrödinger equation coupled to a simulation of a sequence of electric fields modeling the effects of the Langmuir wave. We present and discuss several line profiles of Lyman and Balmer lines. Full article
(This article belongs to the Special Issue Spectral Line Shapes in Astrophysics and Related Topics)
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Open AccessFeature PaperArticle Line Shape Modeling for the Diagnostic of the Electron Density in a Corona Discharge
Atoms 2017, 5(4), 35; doi:10.3390/atoms5040035
Received: 31 August 2017 / Revised: 23 September 2017 / Accepted: 24 September 2017 / Published: 28 September 2017
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Abstract
We present an analysis of spectra observed in a corona discharge designed for the study of dielectrics in electrical engineering. The medium is a gas of helium and the discharge was performed at the vicinity of a tip electrode under high voltage. The
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We present an analysis of spectra observed in a corona discharge designed for the study of dielectrics in electrical engineering. The medium is a gas of helium and the discharge was performed at the vicinity of a tip electrode under high voltage. The shape of helium lines is dominated by the Stark broadening due to the plasma microfield. Using a computer simulation method, we examine the sensitivity of the He 492 nm line shape to the electron density. Our results indicate the possibility of a density diagnostic based on passive spectroscopy. The influence of collisional broadening due to interactions between the emitters and neutrals is discussed. Full article
(This article belongs to the Special Issue Spectral Line Shapes in Astrophysics and Related Topics)
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Open AccessFeature PaperArticle Stark-Zeeman Line Shape Modeling for Magnetic White Dwarf and Tokamak Edge Plasmas: Common Challenges
Atoms 2017, 5(4), 36; doi:10.3390/atoms5040036
Received: 23 August 2017 / Revised: 21 September 2017 / Accepted: 29 September 2017 / Published: 4 October 2017
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Abstract
The shape of atomic spectral lines in plasmas contains information on the plasma parameters, and can be used as a diagnostic tool. Under specific conditions, the plasma located at the edge of tokamaks has parameters similar to those in magnetic white dwarf stellar
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The shape of atomic spectral lines in plasmas contains information on the plasma parameters, and can be used as a diagnostic tool. Under specific conditions, the plasma located at the edge of tokamaks has parameters similar to those in magnetic white dwarf stellar atmospheres, which suggests that the same line shape models can be used. A problem common to tokamak and magnetic white dwarfs concerns the modeling of Stark broadening of hydrogen lines in the presence of an external magnetic field and the related Zeeman effect. In this work, we focus on a selection of issues relevant to Stark broadening in magnetized hydrogen plasmas. Various line shape models are presented and discussed through applications to ideal cases. Full article
(This article belongs to the Special Issue Spectral Line Shapes in Astrophysics and Related Topics)
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Open AccessArticle Discrepancies in Atomic Data and Suggestions for Their Resolutions
Atoms 2017, 5(4), 37; doi:10.3390/atoms5040037
Received: 16 February 2017 / Revised: 21 September 2017 / Accepted: 27 September 2017 / Published: 9 October 2017
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Abstract
The analysis and modelling of a range of plasmas (for example, astrophysical, laser- produced and fusion) require atomic data for a number of parameters, such as energy levels, radiative rates and electron impact excitation rates, or equivalently, the effective collision strengths. Such data
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The analysis and modelling of a range of plasmas (for example, astrophysical, laser- produced and fusion) require atomic data for a number of parameters, such as energy levels, radiative rates and electron impact excitation rates, or equivalently, the effective collision strengths. Such data are desired for a wide range of elements and their many ions, although all elements are not useful for all types of plasmas. Since measurements of atomic data are mostly confined to only a few energy levels of some ions, calculations for all parameters are highly important. However, often, there are large discrepancies among different calculations for almost all parameters, which makes it difficult to apply the data with confidence. Many such discrepancies (and the possible remedies) were discussed earlier (Fusion Sci. Technol. 2013, 63, 363). Since then, many more anomalies for almost all of these atomic parameters have been noticed. Therefore, this paper is a revisit of various atomic parameters to highlight the large discrepancies, their possible sources and some suggestions to avoid these, so that comparatively more accurate and reliable atomic data may be available in the future. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
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Open AccessArticle THz/Infrared Double Resonance Two-Photon Spectroscopy of HD+ for Determination of Fundamental Constants
Atoms 2017, 5(4), 38; doi:10.3390/atoms5040038
Received: 1 September 2017 / Revised: 1 October 2017 / Accepted: 6 October 2017 / Published: 12 October 2017
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Abstract
A double resonance two-photon spectroscopy scheme is discussed to probe jointly rotational and rovibrational transitions of ensembles of trapped HD+ ions. The two-photon transition rates and lightshifts are calculated with the two-photon tensor operator formalism. The rotational lines may be observed with
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A double resonance two-photon spectroscopy scheme is discussed to probe jointly rotational and rovibrational transitions of ensembles of trapped HD+ ions. The two-photon transition rates and lightshifts are calculated with the two-photon tensor operator formalism. The rotational lines may be observed with sub-Doppler linewidth at the hertz level and good signal-to-noise ratio, improving the resolution in HD+ spectroscopy beyond the 10−12 level. The experimental accuracy, estimated at the 10−12 level, is comparable with the accuracy of theoretical calculations of HD+ energy levels. An adjustment of selected rotational and rovibrational HD+ lines may add clues to the proton radius puzzle, may provide an independent determination of the Rydberg constant, and may improve the values of proton-to-electron and deuteron-to-proton mass ratios beyond the 10−11 level. Full article
(This article belongs to the Special Issue High Precision Measurements of Fundamental Constants)
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Other

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Open AccessFeature PaperProject Report Photometric and Polarimetric Interpretation of Blazar AO 0235+164 Behaviour
Atoms 2017, 5(4), 39; doi:10.3390/atoms5040039
Received: 7 September 2017 / Revised: 30 September 2017 / Accepted: 3 October 2017 / Published: 19 October 2017
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Abstract
Among the great number of controversial issues, the most topical one both for theoretical and observational astrophysics presently is a problem of active galactic nuclei investigation. To explain the behaviour of blazar AO 0235+164, which has been under observation at the LX200 telescope
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Among the great number of controversial issues, the most topical one both for theoretical and observational astrophysics presently is a problem of active galactic nuclei investigation. To explain the behaviour of blazar AO 0235+164, which has been under observation at the LX200 telescope (SPbSU) since 2002, the method of analyzing developed by V.A. Hagen-Thorn and S.G. Marchenko was applied. It is based on the assumption that in the case of observational data lying on the straight line in the absolute Stokes parameters space { I , Q , U } (for polarimetry) and the fluxes space { F 1 , . . F n } (for photometry), relative Stokes parameters and relative flux ratios stay unchanged , and consequently, only one source is corresponding to the variability of general value of flux. In this paper, the photometric and polarimetric interpretation of blazar behaviour is presented. Furthermore, the flux and flux–flux diagrams are obtained for three periods of object monitoring: 2006–2007 and 2008–2009 (outbursts) and 2009–2016 (decline with 2015 outburst). Full article
(This article belongs to the Special Issue Spectral Line Shapes in Astrophysics and Related Topics)
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