Turbulence and Anomalous Transport in Magnetized Plasmas: Hints from the Reversed Field Pinch Configuration

Abstract

The properties of plasma turbulence in the outer region of the Reversed Field Pinch experiments RFX and EXTRAP‐T2R are reviewed. The statistical properties of fluctuations in the range of scales relevant for transport are presented. The observation of coherent structures emerging from the background turbulence and their interpretation in terms of vortices is reported. The interplay between these structures and the mean E×B flow of the plasma is demonstrated with emphasis to the action on the preferential rotation direction. The effect on the particle transport induced by the background turbulence and by the structures is discussed. Finally the methods tested to control turbulence and to mitigate the related transport are illustrated and discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Transport mechanisms in the outer region of RFX-mod

“…Although the k-spectrum is rather broad, in particular, at higher frequency, an almost linear dispersion relation may be estimated at least up to 30 kHz, from which an evaluation of the toroidal propagation can be done. The two estimates of the toroidal flow are found comparable as can be observed from figure 13, and at least for the GPI the obtained flow has been found consistent with the E × B drift as obtained from the plasma potential gradient [38]. For both estimates it is clearly found that the flow is higher at lower values of the normalized density and tends to saturate at a value of around 20 km s −1 for n ∼ (0.35-0.4) n G .…”

Electrostatic turbulence in the edge of TPE-RX and driving mechanisms

“…This could be caused by the poor statistics, since the negative events in δn e are less then the positive ones, as will be pointed out at the end of this paper. A similar phase relation described here for the GPI signal I and the floating potential is normally found between the floating potential signal and the ion saturation current I s measured by the electrostatic probes in fusion devices, as shown for example in [19]. Thus, as the fluctuations of the ion saturation current reflect mainly the fluctuations of the local electron density and they are only a little affected by the electron temperature (I s ∝ n e √ T e ), the fluctuations of the light emission measured by the GPI are mainly proportional to n e .…”