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

2018 ◽  
Author(s):  
Roshin Raj Sheeba ◽  
Mohammed Koubiti ◽  
Nelly Bonifaci ◽  
Franck Gilleron ◽  
Jean-Christophe Pain ◽  
...  
Keyword(s):  
Emission Line ◽  
Corona Discharge ◽  
Line Shape ◽  
Diagnostic Technique ◽  
Parameter Determination ◽  
Line Profiles ◽  
Plasma Parameters ◽  
Line Shapes ◽  
Physical Effects

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 abundances. However, using spectroscopy needs appropriate line shape codes retaining all the physical effects governing the emission line profiles. This requires 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 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 experimental spectra from a helium corona discharge at low pressure 1- 2 bars, are presented.

scholarly journals Efficient polynomial analysis of magic-angle spinning sidebands and application to order parameter determination in anisotropic samples

2021 ◽  
Vol 2 (2) ◽  
pp. 589-606
Author(s):  
Günter Hempel ◽  
Paul Sotta ◽  
Didier R. Long ◽  
Kay Saalwächter
Keyword(s):  
Chemical Shift ◽  
Magic Angle Spinning ◽  
Parameter Determination ◽  
Magic Angle ◽  
Chemical Shift Tensors ◽  
Line Shapes ◽  
Fitting Procedure ◽  
The Common ◽  
Angle Spinning

Abstract. Chemical shift tensors in 13C solid-state NMR provide valuable localized information on the chemical bonding environment in organic matter, and deviations from isotropic static-limit powder line shapes sensitively encode dynamic-averaging or orientation effects. Studies in 13C natural abundance require magic-angle spinning (MAS), where the analysis must thus focus on spinning sidebands. We propose an alternative fitting procedure for spinning sidebands based upon a polynomial expansion that is more efficient than the common numerical solution of the powder average. The approach plays out its advantages in the determination of CST (chemical-shift tensor) principal values from spinning-sideband intensities and order parameters in non-isotropic samples, which is here illustrated with the example of stretched glassy polycarbonate.

Experimental Study of Ion Dynamic Effects in Overlapping Helium Lines at Low Densities

1983 ◽  
Vol 38 (1) ◽  
pp. 37-46 ◽  
Author(s):  
A. Piel ◽  
H. Richter
Keyword(s):  
Experimental Study ◽  
High Purity ◽  
Line Shape ◽  
Plasma Source ◽  
Line Profiles ◽  
Dynamic Effects ◽  
Electron Densities ◽  
Plasma Parameters ◽  
Critical Comparison

Abstract The line profiles of the overlapping helium lines 447.1 nm and 492.2 nm have been investigated in an improved plasma source of high purity at electron densities of 1 × 1021 m−3 and 3 × 1021 m−3 . The plasma parameters Ne, Te and T0 were determined carefully by independent diagnostics, which enables a critical comparison with existing theories (BCS II and MMM). We observed ion dynamic effects which considerably modify the line shape of the forbidden components. Our experiments extend the existing observations towards higher ion temperatures. Systematic trends observed earlier are critically discussed.

The impact theory of spectral line shapes: a paradigm shift

2013 ◽  
Vol 91 (11) ◽  
pp. 879-895 ◽  
Author(s):  
A.D. May ◽  
W.-K. Liu ◽  
F.R.W. McCourt ◽  
R. Ciuryło ◽  
J. Sanchez-Fortún Stoker ◽  
...  
Keyword(s):  
Spectral Line ◽  
Line Shape ◽  
Paradigm Shift ◽  
Wigner Distribution ◽  
Kinetic Equations ◽  
Line Profiles ◽  
Line Shapes ◽  
Experimental Line ◽  
Impact Theory ◽  
The Impact

An overview of the binary collision impact theory of spectral line shapes has been given to provide a unified statistical mechanical approach to line-shape theory, laser theory, nonlinear optics, and transport phenomena in dilute gases. The computation of spectral line profiles corresponding to those obtained from ultra-high-resolution spectral line-shape measurements requires numerical ab initio calculation of scattering amplitudes directly from the underlying dynamics of collisions between radiatively active molecules and their perturbers. The Wigner distribution function–density matrix is utilized to describe the kinetic theory of spectral line shapes and to discuss the various collisional processes that contribute to the kernel of kinetic equations. The influence of features of the potential energy surface on spectral parameters is also discussed, and the importance of comparing experimental line profiles directly with numerically computed line shapes obtained from reliable interaction potentials is emphasized. This contrasts sharply with the universal practice of comparing experimental line widths and shifts using some average or approximate theoretical scattering cross-sections and it contrasts sharply with fitting experimental profiles to some convenient analytical line-shape model; hence the phrase “a paradigm shift” in the title of this work.

Determination of edge plasma parameters by a genetic algorithm analysis of spectral line shapes

2004 ◽  
Vol 44 (13) ◽  
pp. 289-293 ◽  
Author(s):  
Y. Marandet ◽  
P. Genesio ◽  
L. Godbert-Mouret ◽  
M. Koubiti ◽  
R. Stamm ◽  
...  
Keyword(s):  
Genetic Algorithm ◽  
Spectral Line ◽  
Edge Plasma ◽  
Algorithm Analysis ◽  
Plasma Parameters ◽  
Line Shapes

scholarly journals Fast Rotating Stars: Effect of the Aspect Angle on Line Profiles

2004 ◽  
Vol 215 ◽  
pp. 23-24 ◽  
Author(s):  
Y. Frémat ◽  
J. Zorec ◽  
A. M. Hubert ◽  
M. Floquet ◽  
N. Leister ◽  
...  
Keyword(s):  
Spectral Line ◽  
Parameter Determination ◽  
Fundamental Parameter ◽  
Line Profiles ◽  
Rotating Stars ◽  
Chemical Abundances ◽  
Aspect Angle ◽  
Line Shapes ◽  
Density Distributions ◽  
On Line

Fast rotation is expected to flatten the star and to produce non uniform temperature and density distributions (i.e. gravitational darkening). While the flattening mostly increases the absolute flux level of the energy distribution, gravitational darkening makes an equator-on star apparently cooler than a star seen through the pole. Both effects (Collins et al. 1991) influence the colours and the location of the star in the HR diagram but also, in a more subtle way, its spectral line profiles. More particularly, in early B type stars, gravitational darkening tends to privilege at the poles the formation of the ions with the highest ionization potentials and directly affects line formation. Consequently, most spectral line shapes - and especially the weakest ones - become aspect angle dependent which in several cases may play a role in the fundamental parameter determination procedures or even in the determination of stellar chemical abundances.

scholarly journals Hydrogen Line Shapes in Plasmas with Large Magnetic Fields

Atoms ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 74
Author(s):  
Joël Rosato
Keyword(s):  
Plasma Diagnostics ◽  
Line Shape ◽  
Zeeman Effect ◽  
Line Profiles ◽  
Stark Broadening ◽  
Hydrogen Line ◽  
Line Shapes ◽  
Code Comparison ◽  
Computer Simulation Technique ◽  
Quadratic Zeeman Effect

We report on hydrogen line shape calculations in the presence of an external magnetic field, at conditions such that the quadratic Zeeman effect is important. The latter is described through a term proportional to B2 in the Hamiltonian, accounting for atomic diamagnetism. It provides a shift and an asymmetry on Lorentz triplets, and it leads to the occurrence of forbidden components. Motivated by investigations performed at the fifth edition of the Spectral Line Shape in Plasmas (SLSP5) code comparison workshop, we perform new calculations of hydrogen Lyman line profiles. Field values representative of magnetized white dwarf atmosphere conditions are taken. The calculations are done using a computer simulation technique, designed for Stark broadening modeling. A discussion of the results is done in the framework of plasma diagnostics.

On the Determination of the Optical Depth of 21-cm Emission Line Profiles

1972 ◽  
Vol 77 ◽  
pp. 711 ◽  
Author(s):  
K. Rohlfs ◽  
E. Braunsfurth ◽  
U. Mebold
Keyword(s):  
Emission Line ◽  
Optical Depth ◽  
Line Profiles

scholarly journals On the Time Scales of Optical Variability of AGN and the Shape of Their Optical Emission Line Profiles

Atoms ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 26
Author(s):  
Edi Bon ◽  
Paola Marziani ◽  
Predrag Jovanović ◽  
Nataša Bon
Keyword(s):  
Emission Line ◽  
Active Galactic Nuclei ◽  
Time Scales ◽  
Accretion Disks ◽  
Galactic Nuclei ◽  
Optical Emission ◽  
Light Curves ◽  
Optical Variability ◽  
Line Profiles ◽  
Line Shapes

The mechanism of the optical variability of active galactic nuclei (AGN) is still very puzzling. It is now widely accepted that the optical variability of AGN is stochastic, producing red noise-like light curves. In case they were to be periodic or quasi-periodic, one should expect that the time scales of optical AGN variability should relate to orbiting time scales of regions inside the accretion disks with temperatures mainly emitting the light in this wavelength range. Knowing the reverberation scales and masses of AGN, expected orbiting time scales are in the order of decades. Unfortunately, most of monitored AGN light curves are not long enough to investigate such time scales of periodicity. Here we investigate the AGN optical variability time scales and their possible connections with the broad emission line shapes.

scholarly journals Modelling of Mg II lines in solar prominences

2019 ◽  
Vol 625 ◽  
pp. A30 ◽  
Author(s):  
P. J. Levens ◽  
N. Labrosse
Keyword(s):  
Radiative Transfer ◽  
Emission Measure ◽  
Line Profiles ◽  
Plasma Parameters ◽  
One Dimensional ◽  
Line Shapes ◽  
Physical Conditions ◽  
Solar Prominences ◽  
Wide Range ◽  
Hydrogen Lines

Context. Observations of the Mg II h and k lines in solar prominences with IRIS reveal a wide range of line shapes from simple non-reversed profiles to typical double-peaked reversed profiles, and with many other possible complex line shapes. The physical conditions responsible for this variety are not well understood. Aims. Our aim is to understand how physical conditions inside a prominence slab influence shapes and properties of emergent Mg II line profiles. Methods. We compute the spectrum of Mg II lines using a one-dimensional non-LTE radiative transfer code for two large grids of model atmospheres (isothermal isobaric, and with a transition region). Results. The influence of the plasma parameters on the emergent spectrum is discussed in detail. Our results agree with previous studies. We present several dependencies between observables and prominence parameters which will help with the interpretation of observations. A comparison with known limits of observed line parameters suggests that most observed prominences emitting in Mg II h and k lines are cold, low-pressure, and optically thick structures. Our results indicate that there are good correlations between the Mg II k line intensities and the intensities of hydrogen lines, and the emission measure. Conclusions. One-dimensional non-LTE radiative transfer codes allow us to understand the main characteristics of the Mg II h and k line profiles in solar prominences, but more advanced codes will be necessary for detailed comparisons.

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