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(TH/P1-16) Theory of Cross Phase-Induced Transport Suppression in Strongly Sheared Flow

P.W. Terry¹⁾, A.S. Ware²⁾, D.E. Newman^3)
 
1) University of Wisconsin-Madison, Madison, Wisconsin, USA
²⁾ University of Montana-Missoula, Missoula, Montana, USA
³⁾ University of Alaska at Fairbanks, Fairbanks, Alaska, USA

Abstract.  Theoretical work is described that elucidates the critical role played by the cross phase between transport-causing fluctuations in transport barriers. This work details how the cross phase contributes to flux reduction in the presence of flow shear, and accounts for a number of experimental observations that cannot be understood solely in terms of the response of fluctuation magnitudes. It is found that 1) in collisionless trapped electron mode turbulence the cross phase, particle flux, growth rate, and nonlinear coupling all depend on the density-potential correlation, and hence all decrease with flow shear. The decrease of growth rate and nonlinear coupling offset in the saturation balance, leaving fluctuation levels largely unchanged. 2) In strong shear, the cross phase for an advected scalar responds more strongly to flow shear than do the amplitudes, allowing cross-phase suppression to dominate the flux reduction produced by flow shear. 3) The interplay of magnetic shear and flow shear inhomogeneities can lead to localized regions of negative cross phase, and therefore inward flux. All three of these types of behavior are observed in experiment.

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