Zonal Flows Driven by Small-Scale Drift-Alfven Modes

Generation of zonal flows by small-scale drift-Alfven modes is investigated by adoptingthe approach of parametric instability with the electron polarization drift included.The zonalmode can be excited by primary modes propagating at both electron and ion diamagnetic driftdirections in contrast to the assertion in previous studies that only primary modes propagatingin the ion diamagnetic drift directions can drive zonal instabilities.Generally,the growth rate ofthe driven zonal mode is in the same order as that in previous study.However,different from theprevious work,the growth rate is no longer proportional to the difference between the diamagneticdrift frequencies of electrons and ions.