Effects of sheared flows on ion-temperature-gradient-driven turbulent transport

Abstract

Previous studies of the ion-temperature-gradient (ITG) driven turbulence are expanded to include the effect of sheared E X B flows in sheared magnetic fields. The radial eigenmodes are shown to substantially change character by shifting the modes off the rational surface. The new mode structure and growth rate directly affects the transport of both thermal energy and momentum in the sheared flows. The growth rate first increases with small shear flow and then decreases. The theoretical correlation of the shear flow with the thermal transport is important with respect to the transitions observed in tokamaks of a low (L mode) to a high (H mode) thermal confinement state as a function of the poloidal rotation velocity in the shear flow layer. The three-dimensional nonlinear simulations show that the anomalous ion thermal diffusivity is reduced significantly when dv@/dx ≃ 2(cs/Ls) √(1 + ηi) Ti/Te. This condition is thought to be satisfied in a boundary layer in tokamaks with shear flow. © 1992 American Institute of Physics.