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In the vicinity of the plasma edge of a magnetic fusion device, several populations of neutral emitters and ionic particles coexist. An elastic collision mechanism between ions and neutrals has been recently identified as a significant relaxation process between these populations. We have studied the relaxation of the neutral particle velocity distribution function (VDF) with a random walk model in velocity space. This VDF is shown to obey a Fokker-Planck equation in the diffusive case. For cases where a non-diffusive regime in the velocity space is assumed, our approach leads to a VDF with an asymptotic power law. The model is applied to the observation of the Deuterium Balmer 3-2 transition, D[alpha], spectra observed in the edge of the Tore-Supra Tokamak. The fit of observed asymmetric spectra requires the use of the relaxation model for three different populations of neutrals. A possible explanation for the wing decay of symmetric D[alpha] is the presence of a superdiffusive transport in velocity space.

Additional information

Authors: KOUBITI M ET AL, PIIM, Université de Provence, Marseille (FR);ESCARGUEL A ET AL, Association Euratom-CEA Cadarache, St. Paul-lez-Durance (FR)
Bibliographic Reference: An article published in: Journal of Quantitative Spectroscopy and Radiative Transfer, Volume 71, Issues 2-6, 15 October 2001, pp. 455-463
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