Analytical and numerical studies of electron-temperature-gradient-driven inverse cascade of energy*

Recent numerical results demonstrated that the interaction between ion-scale and electron-scale turbulence in tokamaks plays an important role in setting the overall level of energy transport (Howard et. al, 2015). One of the principal cross-scale interaction mechanisms is the inverse cascade of energy from electron scales to ion scales driven by unstable electron-temperature-gradient (ETG) modes. This inverse cascade mechanism is not understood. We report on a set of novel fluid-kinetic simulations and analytical results aimed at elucidating the physical mechanisms underpinning the ETG inverse cascade in slab geometry, using a reduced gyrokinetic model (Zocco and Schekochihin, 2011).