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

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.