Interaction among different spatio-temporal scale fluctuations through zonal flows

Zonal flows generated by fluctuations on some scale are expected to affect fluctuations on other different spatial-temporal scales in addition to regulating their own fluctuation. As an example, here we discuss ITG turbulence embedded in a small scale ETG-driven zonal flow based on 3-dimensional gyro-fluid simulations. At first, we identified the ETG-driven zonal spectrum and found that the zonal flows are enhanced in higher pressure and lower magnetic shear plasma, leading to a self-organized high energy state. Further, we found a new suppression mechanism of the long wavelength ITG mode by the small-scale ETG-driven zonal flows, namely, the radially non-local mode coupling and the associated energy transfer. Besides the role of suppression in ITG turbulence, we have for the first time observed intermittent and/or bursting behaviour in the ion heat transport originating from the complicated mutual interaction among ETG-driven zonal flows, ITG turbulence, and the associated ITG-driven zonal flows. (author)