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Atoms 2014, 2(2), 178-194; doi:10.3390/atoms2020178

Review of Langmuir-Wave-Caused Dips and Charge-Exchange-Caused Dips in Spectral Lines from Plasmas and their Applications

1
Sorbonne Universités Pierre et Marie Curie, 75252 Paris CEDEX 5, France
2
Ecole Polytechnique, LULI, F-91128 Palaiseau CEDEX, France
3
Physics Department, 206 Allison Lab, Auburn University, Auburn, AL 36849, USA
4
Institute of Physics v.v.i., Academy of Sciences CR, 18221 Prague, Czech Republic
*
Author to whom correspondence should be addressed.
Received: 22 January 2014 / Revised: 25 March 2014 / Accepted: 30 April 2014 / Published: 13 May 2014
(This article belongs to the Special Issue Spectral Line Shapes in Plasmas)
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Abstract

We review studies of two kinds of dips in spectral line profiles emitted by plasmas—dips that have been predicted theoretically and observed experimentally: Langmuir-wave-caused dips (L-dips) and charge-exchange-caused dips (X-dips). There is a principal difference with respect to positions of L-dips and X-dips relative to the unperturbed wavelength of a spectral line: positions of L-dips scale with the electron density Ne roughly as Ne1/2, while positions of X-dips are almost independent of Ne (the dependence is much weaker than for L-dips). L-dips and X-dips phenomena are important, both fundamentally and practically. The fundamental importance is due to a rich physics behind each of these phenomena. L-dips are a multi-frequency resonance phenomenon caused by a single-frequency (monochromatic) electric field. X-dips are due to charge exchange at anticrossings of terms of a diatomic quasi-molecule, whose nuclei have different charges. As for important practical applications, they are as follows: observations of L-dips constitute a very accurate method to measure the electron density in plasmas—a method that does not require knowledge of the electron temperature. L-dips also allow measuring the amplitude of the electric field of Langmuir waves—the only spectroscopic method available for this purpose. Observations of X-dips provide an opportunity to determine rate coefficient of charge exchange between multi-charged ions. This is an important reference data, virtually inaccessible by other experimental methods. The rate coefficients of charge exchange are important for magnetic fusion in Tokamaks, for population inversion in the soft x-ray and VUV ranges, for ion storage devices, as well as for astrophysics (e.g., for the solar plasma and for determining the physical state of planetary nebulae). View Full-Text
Keywords: dips in spectral line profiles; diagnostic of Langmuir waves amplitude; diagnostic of electron density in plasmas; method for measuring charge exchange rates dips in spectral line profiles; diagnostic of Langmuir waves amplitude; diagnostic of electron density in plasmas; method for measuring charge exchange rates
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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MDPI and ACS Style

Dalimier, E.; Oks, E.; Renner, O. Review of Langmuir-Wave-Caused Dips and Charge-Exchange-Caused Dips in Spectral Lines from Plasmas and their Applications. Atoms 2014, 2, 178-194.

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