  During the past years the understanding of the multi-scale interaction
problems have increased significantly. However, at present there exists a range
of different analytical models for investigating multi-scale interactions and
hardly any specific comparisons have been performed among these models. In this
work, two different models for the generation of zonal flows from
ion-temperature-gradient (ITG) background turbulence are discussed and
compared. The methods used is the coherent mode coupling model and the wave
kinetic equation model (WKE). It is shown that the two models give
qualitatively the same results even though the assumption on the spectral
difference is used in the (WKE) approach.
