Interplay between zonal flows/GAMs and ITG turbulence in tokamak plasmas

Miyato, Naoaki; Kishimoto, Yasuaki; Li, J. Q.*

Zonal flow behaviour and its effect on turbulent transport in tokamak plasmas are investigated by global fluid simulations of electrostatic ion temperature gradient (ITG) driven turbulence. It is found that oscillatory zonal flows called geodesic acoustic modes (GAMs) appearing in a high (safety factor) region have the same frequency in a certain radial region whose width is almost proportional to in positive shear tokamaks, and the radial wavelength of the GAMs is proportional to , where is an ion Larmor radius and is a minor radius of a plasma. The turbulent transport is affected by the nonlocal behaviour of the GAMs. It seems that the radial width of the region connecting a low tranport region where the stationary zonal flows are dominant with a high transport region where the GAMs are dominant is related with the nonlocal width of the GAMs. In reversed shear tokamaks with high , turbulent transport is high even in a minimum region because the GAMs are dominant. The turbulent transport is reduced in the minimum region when is enough low to damp the GAMs. The difference of zonal flow behaviour causes the difference of the turbulent transport and may trigger formation of ion internal transport barriers in both positive and reversed shear tokamaks.