(TH/P2-11) Interplay between zonal flows/GAMs and ITG turbulence in tokamak plasmas

N. Miyato1), Y. Kishimoto2)1), J. Q. Li2)
 
1) Japan Atomic Energy Agency, Naka, Japan
2) Kyoto University, Uji, Japan

Abstract.  Zonal flow (ZF) behavior and its effect on turbulent transport in tokamak plasmas are investigated by global fluid simulations of electrostatic ion temperature gradient (ITG) driven turbulence. In the simulations, the frequency of oscillatory ZFs called geodesic acoustic modes (GAMs) appearing in a high q (safety factor) region does not vary continuously with a radius, but its radial variation is step-like and the GAMs have the same frequency in a certain radial region. It is found that the radial width of the region in which the GAMs have the same frequency is almost proportional to the geometric mean of an ion Larmor radius and a minor radius of a plasma in positive shear tokamaks, while the radial wavelength of the GAMs is proportional to the ion Larmor radius. Since the GAM frequencies are close to those of the ITG turbulence, the GAM dominant region is a high transport region and the statinoary ZF region is a low transport region. The turbulent transport is affected by the nonlocal behavior of the GAMs. It seems that the radial width of the region connecting the low tranport region where the stationary ZFs are dominant with the high transport region where the GAMs are dominant is related with the nonlocal width of the GAMs.

Full paper available (PDF)