Role of nonthermal velocity fluctuations on anomalous impurity heating in the TJ-I tokamak

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

“…In contrast, the temperature of C 2+ exhibits high "apparent" temperature values that decrease as the density increases (see figure 5(c)). This might be due to the influence of plasma velocity turbulence on different ions, already reported by us for highly ionized ions [12,13], that is more important for the higher the mass ions. In general, C 2+ and C + exhibit more significant temporal temperature variations than other ions.…”

“…However, it is generally observed that some types of plasma turbulence tend to decrease, when increasing the electron plasma density, see ref. [12]. That might be a hint to look more deeply into this effect in the future, to figure out whether this behaviour of C 2+ temperature could be caused by turbulent velocities.…”

“…We must remark that although we cannot compare data for different ions in the same discharge, and this could be the reason for some of the differences, but we do not believe that it is the only explanation. Since carbon mass is significantly higher than that of Li and He, carbon temperatures might be more influenced by the effect of turbulent velocities on the kinetic temperature deduced form line width, see our references [12,13] for a more detailed discussion of this effect.…”

Turbulence and line shape formation in plasmas

“…The relative contribution of turbulence to the line width becomes more and more pronounced as M increases, and in fact observing different lines from several thermalized impurities is a well established way of disentangling turbulent from thermal broadening in optically thin plasmas [19,20]. It should be noted that there are situations where W(u) is non-Gaussian, and where the measured profile is therefore non-Gaussian [18].…”

On the determination of edge Ti profiles by a supersonic He beam in TJ-II

“…On the other hand, the toroidal dispersion of injected impurities has been analyzed in terms of local ion temperature and plasma rotation, but the electron parameter profiles need to be independently determined for the simulations [2]. More conventional methods for local Ti measurements, as passive Dopplerresolved spectroscopy or CXRS are of limited application to the edge region and are sensitive to other line-broadening mechanisms [3]. Moreover, electric probes such the retarding field analyzer (RFA) diagnostic are intrinsically perturbative if inserted beyond the LCFS.…”