Spectral Line Shape Modelling and Ion Temperature Fluctuations in Tokamak Edge Plasmas

Abstract

In this work, we use a passive advection model for ion temperature fluctuations, in order to investigate their effects on Doppler Spectral line shapes. The relevance of the model is discussed in the framework of the Braginskii equations, and the subsequent Probability Density Function evaluation relies on results obtained in neutral fluids. The resulting Doppler line profiles are shown to exhibit characteristic exponential tails.

Probing the edge ion temperature by passive Doppler spectroscopy in the TJ-II stellarator

“…Recently, the spectral line shape and T i fluctuations have been extensively modeled [10], at conditions relevant to the edge of a magnetic fusion device, but scarce effort on the experimental side of using passive spectroscopy can be found in the literature notwithstanding the excellent and detailed work performed in the TEXTOR tokamak [11]. That paper deals with all the critical issues of this kind of measurements, with the exception of the possible effect of ion mass on Doppler ion temperature measurements, which can be observed only when measurements are taken with thermalized ions of significantly different mass.…”

“…In high magnetic field devices, the complications added to the line width analysis by the influence of the Zeeman effect have the advantage that some information on the spatial origin of the emission can be recovered [9] due to the variation of the magnetic field along the line-ofsight. Recently, the spectral line shape and T i fluctuations have been extensively modelled [10], under conditions relevant to the edge of a magnetic fusion device, but scant effort on the experimental side of using passive spectroscopy can be found in the literature notwithstanding the excellent and detailed work performed in the TEXTOR tokamak [11]. That paper deals with all the critical issues of these kinds of measurements, with the exception of the possible effect of ion mass on Doppler ion temperature measurements, which can be observed only when measurements are taken with thermalized ions of significantly different masses.…”

Turbulence and line shape formation in plasmas

“…This result, which shows that W(Y) can be obtained from an ensemble average, provided turbulence is homogeneous, is useful when using simplified turbulence models to calculate W [12]. In the context of magnetic fusion plasmas, the situation with respect to spatial integration depends on the details of the geometry, mainly the direction of the LOS with respect to that of the magnetic field B.…”

Spectral Line Shapes as a Diagnostic Tool in Magnetic Fusion

“…It has been shown [5] that the measured profile may be expressed as an integral over the fluid variables of the local profile, weighed by the probability density function (PDF) of the fluctuating hydrodynamic variables. The PDF of only one hydrodynamic variable has been studied theoretically [35,36], and has been measured in a few devices [37,38]. Since this quantity is of great interest for characterizing the edge plasma turbulence, the link made with the line shape may lead to a valuable diagnostic of turbulence by spectroscopy.…”