Spectroscopic analysis of the plasma-neutral relaxation near to the plasmaboundary

(x)(O) In the vicinity of the plasma edge of a magnetic fusion device, seve ral 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 stu died 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 diff usive 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 th e Deuterium Balmer 3-2 transition, D alpha, spectra observed in the edge of the Tore-Supra Tokamak. The fit of observed asymmetric spectra requires th e use of the relaxation model for three different populations of neutrals. A possible explanation for the wing decay of symmetric D alpha is the prese nce of a superdiffusive transport in velocity space. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.