Identification of Zonal Flows and Their Spatial Distribution in the TJ-II Stellarator Plasmas

For low-frequency (0 < f < 20 kHz) plasma electric potential oscillations, measured in two toroidally spaced vertical cross-sections of the TJ-II stellarator (R = 1.5 m, a = 0.22 m, B = 1T) using double heavy ion beam probe diagnostics, long-range correlations are observed, as well as their toroidal and poloidal symmetry n = m = 0. It is shown that long-range correlations do not have a magnetic or density component. Thus, the low-frequency symmetric structures of the electric potential found in the hot plasma area are zonal flows. Their quantitative characteristic is the square coherence coefficient gamma(2). For the first time a two-dimensional map of zonal flows (long-range correlations) in the low-density (n) over bar (e) = 0.5 center dot 10(19) m(-3) regime with ECR heating was plotted and their ballooning structure (dominance gamma (2) on the low field side of the vessel) was found. The decrease in the level of electrostatic turbulence (0 < f < 300 kHz) observed in this region is consistent with the theoretically predicted suppression of broadband turbulence due to zonal flows.