Stabilization of ion temperature gradient mode by small-scale zonal flows

Interaction between large-scale turbulence and small-scale sheared flows is a new issue in magnetized plasmas. In this work, the key interaction mechanism is explored by sampling the large-scale ion temperature gradient (ITG) mode and the small-scale zonal flows driven by the electron temperature gradient turbulence. It is analytically found that the small-scale zonal flows lead to a radially nonlocal mode coupling of ITG fluctuations. It can mediate to transfer the fluctuating free energy of an unstable mode in the longer wavelength region to the stable or damped components at shorter wavelengths. Then, the ITG mode is stabilized. Three-dimensional gyrofluid ITG simulations with an initial value code have confirmed the analytical results very well. The spectral analysis also shows a distinctive feature that this kind of interaction can deform the radial decaying spectrum of ITG fluctuation in the short wavelength region. It may be expected to modulate the turbulent ion heat transport in ITG turbulence