Investigation of the role of temperature fluctuations on spectral line shapes

In low frequency turbulent plasmas, the profile of a Doppler broadened line shape is linked to an effective velocity distribution function (VDF) of the emitters. This distribution is obtained through both a spatial and time average of the local velocity distribution. We study the case of the Balmer α line of deuterium (Dα), in typical conditions encountered in ionising edge plasmas (Ne = 1018–1019 m−3 and Te−Ti = 10–100 eV). We focus this analysis on ion temperature fluctuations, and assume that the acquisition time of the spectrometer is much larger than the typical turbulent time scale. The resulting expression of the effective VDF involves the temperature probability distribution function (PDF). Temperature fluctuations are found to strongly affect the tails of the effective VDF (i.e. line wings), especially when their PDF has a heavy tail. This opens the way for a new spectroscopic analysis of edge plasma turbulence.