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, $B = 1$ T) 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 $\gamma^2$. A two-dimensional map of zonal flows (long-range correlations) in the low-density $\bar{n}_e=0.5\times10^{19}\,$ m$^{-3}$ regime with ECR heating has been plotted for the first time and their ballooning structure (dominance $\gamma^2$ on the low field side of the vessel) has been 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.