scholarly journals Atomic Physics for Hot Plasmas

1988 ◽  
Vol 102 ◽  
pp. 279-282
Author(s):  
L.A. Vainshtein
Keyword(s):  
Atomic Physics ◽  
Cross Sections ◽  
Experimental Test ◽  
Dielectronic Recombination ◽  
Spectral Lines ◽  
Isoelectronic Sequence ◽  
Recombination Rates ◽  
Theoretical Methods ◽  
Laboratory Plasmas ◽  
Charged Ions

This report treats some aspects of how to obtain and apply main atomic characteristics responsible for the intensities and satellite structures of spectral lines in hot plasmas.The experimental test, of theoretical methods and calculated cross- sections σ is often possible only in a plasma, especially for highly charged ions. In this case the rates < υσ >, rather than σ, are measured for different temperature values. Another difficulty is linked to the analysis of a large number of processes which have to be taken into account simultaneously.In laboratory plasmas (usually during an ionization stage) the ionization, excitation and dielectronic recombination rates are measured for numerous ions with Z ≤ 25. They are discussed in the report by H. Griem at this Colloquium. Unfortunately, in some cases the results are not consistent along the isoelectronic sequence and deviate considerably (up to a factor of 1.5 - 2) from those yielded by cross-beam methods, or calculations.

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
Keyword(s):  
Cross Sections ◽  
Impact Ionization ◽  
Emission Measure ◽  
Dielectronic Recombination ◽  
Recombination Rates ◽  
Ionization Equilibrium ◽  
Direct Ionization ◽  
Solar Transition ◽  
Lower Temperature ◽  
Ionization Cross Sections

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.

scholarly journals Investigation of Dominant States in Dielectronic Recombination Rates for Fe-Ions

2003 ◽  
Vol 58 (5-6) ◽  
pp. 346-350
Author(s):  
H. Ramadan ◽  
A. Khazbak ◽  
Ali H. Moussa
Keyword(s):  
Cross Sections ◽  
Theoretical Calculations ◽  
Dielectronic Recombination ◽  
Rate Coefficients ◽  
Recombination Rates ◽  
Semiempirical Formula ◽  
Semi Empirical ◽  
Fe Ions ◽  
Initial Capture ◽  
Good Agreement

Dielectronic recombination (DR) cross sections and rate coefficients are calculated for the isonuclear sequence FeZ+, with Z = 21, 20, 19, 18, 17, and 16, in which L-shell (2p-) excitations are involved during the initial capture. Most of the dominant transitions with Δn ≠ 0, using angular momentum average (AMA) approximation, are considered. It is found that the states 3pnd and 3dnd contribute most to the rate coefficients. In addition, the rates are found to increase with increasing number of electrons in the ion, (i. e. as Z decreases). Moreover, the rate coefficients, αDR, for the studied ions are found to peak around the same energy (kT = 30 Ry). A semi-empirical formula for the total rates α is obtained for the 2p-excitation with Δn ≠ 0 in the case of FeZ+ ions. On comparing both results, the explicit calculations and the results obtained from the semiempirical formula, good agreement is found. The available results for αDR may be considered as a database for future comparison with experimental and theoretical calculations. Comparison of our results with other results show the effect of the empirical rate formula.

Radiative Corrections to Intensities of Dielectronic Satellite Lines Emitted from Helium- and Lithium-Like Argon

1984 ◽  
Vol 86 ◽  
pp. 104-107
Author(s):  
V.L. Jacobs ◽  
J.E. Rogerson
Keyword(s):  
Cross Sections ◽  
Dielectronic Recombination ◽  
Rate Coefficients ◽  
Recombination Mechanism ◽  
Atomic Ions ◽  
Multiply Charged ◽  
Quantum Mechanical Theory ◽  
Laboratory Plasmas ◽  
Resonant Electron ◽  
Dielectronic Satellite

The process of dielectronic recombination has been the subject of intense theoretical activity mainly because of the pioneering work by Burgess (1964), who demonstrated that this process can be the dominant recombination mechanism for multiply-charged atomic ions in low-density high-temperature astrophysical and laboratory plasmas. Recent attempts to measure dielectronic recombination cross sections and rate coefficients have renewed interest in the development of a rigorous quantum-mechanical theory of the resonant electron-ion recombination process. A precise theory is clearly required for the interpretation of the dielectronic satellite lines, which have been found to be of great value in the spectroscopic determination of temperatures, densities, and departures from ionization equilibrium.

Time-resolved spectroscopy of the electrode region in a fluorescent lamp1This article is part of a Special Issue on the 10th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas.

2011 ◽  
Vol 89 (5) ◽  
pp. 627-631
Author(s):  
Thomas Lennartsson ◽  
Sven Huldt
Keyword(s):  
Cross Sections ◽  
Spectral Lines ◽  
Oscillator Strengths ◽  
Electron Collision ◽  
Fluorescent Lamp ◽  
Recombination Rates ◽  
Penning Ionization ◽  
Time Resolved ◽  
International Colloquium ◽  
Electrode Region

In this paper, the ongoing spectroscopic investigations of the plasma inside a fluorescent lamp at Lund Observatory is presented. The intensity of the spectral lines of neutral and singly ionized mercury and krypton in the electrode region in a fluorescent lamp are investigated, both as a function of current through the tube and time resolved during an AC cycle. The results show different dynamics for different spectral lines, which may be due to different population mechanisms and transport phenomena in the discharge. To correctly interpret the data, a model for the electrode region is necessary; however, for this purpose information on processes like electron collision cross-sections, Penning ionization rates, and recombination rates are needed.

The Interpretation of Line Profiles

1977 ◽  
Vol 36 ◽  
pp. 191-215
Author(s):  
G.B. Rybicki
Keyword(s):  
Magnetic Fields ◽  
Atomic Physics ◽  
Velocity Fields ◽  
Spectral Lines ◽  
Inhomogeneous Structure ◽  
The Sun ◽  
Line Profiles ◽  
Physical Phenomena

Observations of the shapes and intensities of spectral lines provide a bounty of information about the outer layers of the sun. In order to utilize this information, however, one is faced with a seemingly monumental task. The sun’s chromosphere and corona are extremely complex, and the underlying physical phenomena are far from being understood. Velocity fields, magnetic fields, Inhomogeneous structure, hydromagnetic phenomena – these are some of the complications that must be faced. Other uncertainties involve the atomic physics upon which all of the deductions depend.

scholarly journals Atomic physics and solar polarimetry

2017 ◽  
Vol 95 (9) ◽  
pp. 847-854 ◽  
Author(s):  
P.G. Judge
Keyword(s):  
Adaptive Optics ◽  
Atomic Physics ◽  
Solar Physics ◽  
Polarized Light ◽  
Initial Study ◽  
Spectral Lines ◽  
Calibration Data ◽  
Science Data ◽  
On Line ◽  
Singly Charged

Major outstanding problems in solar physics relate to solar magnetism. Spectropolarimetry offers the best, and sometimes only, method of obtaining accurate measurements of the Sun’s magnetic field. New 1.5–2 m class telescopes with adaptive optics have come on line, and the Daniel K. Inouye 4 m Solar Telescope (DKIST) will begin observing in 2019. The calibration of polarized light entering such a large and polarizing ground-based telescope represents difficult challenges. This paper explores how special polarization properties of particular atomic transitions may provide calibration data, augmenting or even avoiding time-consuming calibration observations, as well as science data. This initial study concludes that solar spectral lines exist with special polarization properties, allowing the telescope calibration to be determined. The Sun’s visible and infrared spectrum is dominated by lines of neutral atoms and singly charged ions of iron and other complex atoms. Both solar and atomic physics should jointly benefit from telescopic advances, as observers explore regimes of broader wavelength ranges, and higher spatial resolutions and polarimetric sensitivities, than they have reached in the past. Further work is in progress to identify particular transitions of practical use to aid in calibrations.

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