Kishimoto Department of Fundamental Energy Science Graduate School of Energy Science, Kyoto University, Gokasho, Uji, Kyoto 611-0011

Introduction
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In recent experiments in the Columbia Linear Machine (CLM) [@a10] it has been shown that the turbulence suppression of zonal flows is rather weak [@a19]. The suppression of drift wave turbulence by quasi stationary zonal flows has been a major topic during the past years in magnetic fusion research. The zonal flows are poloidally and toroidally symmetric ($k_{\theta} = 0$, $k_{\parallel} = 0$) and radially inhomogeneous ($k_r \neq 0$) flow structures in toroidal plasmas [@a11]- [@a13]. Zonal flows are widely believed to be the main stabilizing mechanism for turbulence and one of the main keys to gain access to high confinement regimes in present and future magnetic confinement fusion devices such as ITER [@a131]. The generation of zonal flows from drift wave turbulence has been extensively studied analytically [@a11], [@a14]- [@a26] and in computer simulations using gyrokinetic [@a35]- [@a38] and advanced fluid models [@a39]- [@a43].

The Ion-Temperature-Gradient (ITG) driven mode is believed to be responsible for the anomalously high heat transport in fusion devices and it has been shown that it is one of the main ingredients in generation of zonal 