The occurrence of staircases in ITG turbulence with kinetic electrons and the zonal flow drive through self-interaction

Abstract

Large scale structures in the E × B shearing rate, known as staircases, are shown to form in nonlinear gyro-kinetic turbulence simulations with kinetic electrons. However, in many cases, a small scale structure in the shearing rate is observed that appears to prevent the formation of staircases. The small scale structures are interpreted to be linked to the self-interaction of turbulent modes connected with the double periodic boundary conditions on the torus. The self-interaction is a newly discovered mechanism for zonal flow generation and is shown to scale proportional to the normalized Larmor radius. The mechanism is also affected by magnetic shear, being weaker at larger values.