Spectral line shapes modeling in turbulent plasmas |
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Authors: | Y Marandet H Capes L Godbert-Mouret M Koubiti J Rosato R Stamm |
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Institution: | 1. PIIM, Université de Provence, Centre de St-Jér?me, 13397, Marseille, France 2. Association Euratom-CEA, CEA/DSM/DRFC, Centre de Cadarache, 13108, Saint-Paul-lez-Durance, France
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Abstract: | In this work we investigate the influence of low
frequency turbulence on Doppler spectral line shapes in magnetized
plasmas. Low frequency refers here to fluctuations whose typical
time scale is much larger than those characterizing the atomic
processes, such as radiative decay, collisions and charge exchange.
This ordering is in particular relevant for drift wave turbulence,
ubiquitous in edge plasmas of fusion devices. Turbulent fluctuations
are found to affect line shapes through both the spatial and time
averages introduced by the measurement process. The profile is
expressed in terms of the fluid fields describing the plasma.
Assuming the spectrometer acquisition time to be much larger than
the turbulent time scale, an ordering generally fulfilled in
experiments, allows to develop a statistical formalism. We proceed
by successively investigating the effects of density, fluid velocity
and temperature fluctuations on the Doppler profile of a spectral
line emitted by a charge exchange population of neutrals. Line
shapes, and especially line wings are found to be affected by ion
temperature or fluid velocity fluctuations, and can in some cases
exhibit a power-law behavior. These effects are shown to be
measurable with existing techniques, and their interpretation in
each particular case would rely on already existing tools. From a
fundamental point of view, this study gives some insights in the
appearance of non-Boltzmann statistics, such as Lévy statistics,
when dealing with averaged experimental data. |
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Keywords: | 32 70 Jz Line shapes widths and shifts 52 35 Ra Plasma turbulence 05 40 Fb Random walks and Levy flights |
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