Identification of Zonal Flows in a Toroidal Plasma

This Letter presents experimental confirmation of the presence of zonal flows in magnetically confined toroidal plasma using an advanced diagnostic system—dual heavy ion beam probes. The simultaneous observation of an electric field at two distant toroidal locations ($\sim 1.5\mathrm{m}$ apart) in the high temperature ($\sim 1\mathrm{k}\mathrm{e}\mathrm{V}$) plasma provides a fluctuation spectrum of electric field (or flow), a spatiotemporal structure of the zonal flows (characteristic radial length of $\sim 1.5\mathrm{c}\mathrm{m}$ and lifetime of $\sim 1.5\mathrm{m}\mathrm{s}$), their long-range correlation with toroidal symmetry $(n=0)$, and the difference in the zonal flow amplitude with and without a transport barrier. These constitute essential elements of turbulence-zonal flow systems, and illustrate one of the fundamental processes of structure formation in nature.