Cross-scale interactions between turbulence driven by electron and ion temperature gradients via sub-ion-scale structures

Maeyama, Shinya*; Watanabe, Tomohiko*; Idomura, Yasuhiro   ; Nakata, Motoki*; Ishizawa, Akihiro*; Nunami, Masanori*

Multi-scale plasma turbulence including electron and ion temperature gradient (ETG/ITG) modes has been investigated by means of electromagnetic gyrokinetic simulations. Triad transfer analyses on nonlinear mode coupling reveal cross-scale interactions between electron and ion scales. One of the interactions is suppression of electron-scale turbulence by ion- scale turbulence, where ITG-driven short-wavelength eddies act like shear flows and suppress ETG turbulence. Another cross-scale interaction is enhancement of ion-scale turbulence in the presence of electron-scale turbulence. This is caused via short-wavelength zonal flows, which are created by the response of passing kinetic electrons in ITG turbulence, suppress ITG turbulence by their shearing, and are damped by ETG turbulence. In both cases, sub-ion-scale structures between electron and ion scales play important roles in the cross-scale interactions.