The impact of radially sheared poloidal flows on ambient edge turbulence in tokamaks is investigated analytically. In the regime where poloidal shearing exceeds turbulent radial scattering, a hybrid time scale weighted toward the former is found to govern the decorrelation process. The coupling between radial and poloidal decorrelation results in a suppression of the turbulence below its ambient value. The turbulence quench mechanism is found to be insensitive to the sign of either the radial electric field or its shear.

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A novel mechanism for the generation and amplification of intrinsic rotation at the low-mode to high-mode transition is presented. The mechanism is one where the net parallel flow is accelerated by turbulence. A preferential direction of acceleration results from the breaking of k ʈ → −k ʈ symmetry by sheared E ϫ B flow. It is shown that the equilibrium pressure gradient contributes a piece of the parallel Reynolds stress, which is nonzero for vanishing parallel flow, and so can accelerate the plasma, driving net intrinsic rotation. Rotation drive, transport, and fluctuation dynamics are treated self-consistently.

Explicit expressions for the neoclassical poloidal and toroidal rotation speeds of primary ion and impurity species are derived via the Hirshman and Sigmar moment approach. The rotation speeds of the primary ion can be significantly different from those of impurities in various interesting cases. The rapid increase of impurity poloidal rotation in the edge region of H-mode discharges in tokamaks can be explained by a rapid steepening of the primary ion pressure gradient. Depending on ion collisionality, the poloidal rotation speed of the primary ions at the edge can be quite small and the flow direction may be opposite to that of the impurities. This may cast considerable doubts on current L to H bifurcation models based on primary ion poloidal rotation only. Also, the difference between the toroidal rotation velocities of primary ions and impurities is not negligible in various cases. In Ohmic plasmas, the parallel electric field induces a large impurity toroidal rotation close to the magnetic axis, which seems to agree with experimental observations. In the ion banana and plateau regime, there can be non-negligible disparities between primary ion and impurity toroidal rotation velocities due to the ion density and temperature gradients. Detailed analytic expressions for the primary ion and impurity rotation speeds are presented, and the methodology for generalization to the case of several impurity species is also presented for future numerical evaluation.

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 ( 1:5 m apart) in the high temperature ( 1 keV) plasma provides a fluctuation spectrum of electric field (or flow), a spatiotemporal structure of the zonal flows (characteristic radial length of 1:5 cm and lifetime of 1:5 ms), 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. Zonal flows-azimuthally symmetric bandlike shear flows-are ubiquitous phenomena in the Universe [1][2][3]; examples include Jovian belts and zones, the terrestrial atmospheric jet stream, the super-rotation of the Venusian atmosphere, and the rotation profile of the solar tachocline. Zonal flows have been expected to be present in magnetically confined toroidal plasmas [4] since the characteristics of drift wave turbulence in the plasmas are analogous to Rossby wave turbulence to cause the phenomena in the rotating planets. Recently, their crucial role in determining the turbulent level and resultant transport has been widely recognized, and the identification of the zonal flows becomes an urgent issue in the fusion research to enhance the prospect of plasma burning in the International Thermonuclear Experimental Reactor [5][6][7].In toroidal plasmas, the zonal flows emerge in electric field fluctuation symmetric m n 0 on magnetic flux surface with finite radial wave numbers (see for review, e.g., [8,9]). Two major branches of zonal flows are expected in magnetic confined toroidal plasmas, i.e., a residual flow of nearly zero frequency, and an oscillatory flow termed geodesic acoustic modes (GAMs) [10,11]. These zonal flows are driven exclusively by nonlinear interactions (or inverse cascade) through energy transfer from the microscopic drift waves. Inversely, the zonal flows regulate the drift wave turbulence and resultant transports. The time-varying E B shearing of zonal flows, similar to the mean flows [12], has a significant effect on plasma turbulence and transport.Direct nonlinear simulations have, in fact, confirmed the appearance of and generation processes for zonal flows [13][14][15][16][17][18][19][20], and their essential role in turbulence and transport of toroidal plasmas. In experiments, however, only indirect signs have been obtained for zonal flows and their role in confinement. Coherent oscillations presumed to be GAMs were detected in measurements with a heavy ion beam probe (HIBP) [21,22], with traditional probes [23,24], and with beam emission spectroscopy using a modified time-delayed-estimation analysis technique [25]. Bicoherence analysis showed an increase in nonlinear interaction between zonal flows and turbule...