Experimental evidence of coupling between local turbulent transport and large scale fluctuations in the ISTTOK edge plasma

Abstract

The interplay between large scale fluctuations and the local turbulent transport has been investigated in the tokamak ISTTOK [C. A. F. Varandas et al., Fusion Technol. 29, 105 (1996)] plasma boundary region. It has been found that the floating potential fluctuations, dominated by low frequency oscillations, exhibit a significant toroidal correlation at large distances that can be attributed to the geodesic acoustic mode. The level of long-distance correlations is strongly bursty, showing a significant degree of coupling with the local electrostatic turbulent transport. Experimental findings show the key role of multiscale physics in the regulation of transport in the edge region of fusion plasmas.

Interaction between mean and fluctuatingE×Bshear flows on the ISTTOK edge plasma

“…It has been found that the long-range correlation increases during bias induced enhanced confinement regimes and when approaching the spontaneous confinement transitions, highlighting the possible role of zonal-flows in edge transport bifurcations. Recent experiments on the ISTTOK tokamak have also identified longdistance correlations in plasma potential fluctuations consistent with the geodesic acoustic mode (GAM) [3], which are also modified in the presence of externally imposed radial electric fields.…”

Poloidal mode structure of long-distance correlation of fluctuations under strong E×B shear in the torsatron TJ-K

“…6 Recently, long-distance correlation in fluctuations was observed in the ISTTOK tokamak. 7,8 The long-distance correlation has been identified as a geodesic acoustic mode and coincide with reduced transport. 8 The importance of long-distance correlations as a fingerprint of the plasma behavior during the development of edge shear flows was emphasized in Ref.…”

Long-distance correlation and zonal flow structures induced by mean E×B shear flows in the biasing H-mode at TEXTOR

“…Very recently, in the TJ-II stellarator 14 an amplification of the LDC by biasing electric fields has been found in potential fluctuations during the transition to improved confinement. In the ISTTOK tokamak, 15 the LDC of potential fluctuations displays bursty features and couples with reduced turbulent transport. The results provoke interests of multiscale physics, i.e., interaction between small-scale turbulence and largescale coherent structures.…”