Generation of electromagnetic structures via modulational instability of drift waves

Abstract

Generation mechanism for large scale electromagnetic structures (blobs) is considered by employing the technique of four-wave interactions (modulational instability). It is shown that primary electrostatic turbulence may generate elongated electromagnetic structures with poloidal modulations. Such structures are principally related to drift-Alfvén waves. The analysis fully takes into account finite ion temperature effects and associated diamagnetic contributions to Reynolds stress. The turbulent generation of blobs has instability growth rates which scale similar to the zonal flow instabilities, γ∼⟨qṼ⟩, where q is a characteristic wave vector of large scale modes, and Ṽ is a characteristic amplitude of the velocity of turbulent fluctuations. This analysis is shown to be fully consistent with results of an earlier analysis by using the wave kinetic equation.