Gyrokinetic Theory and Simulation of Zonal Flows and Turbulence in Helical Systems

Abstract. Gyrokinetic theory and simulations on ion heat transport physics in helical systems have recently been developed. Damping processes of zonal flows driven by ion temperature gradient (ITG) turbulence in helical sys-tems have been analytically investigated based on the gyrokinetic theory as a generalization of the previous work by Rosenbluth and Hinton for tokamaks. A collisionless response function of the zonal flow to given source terms is derived by taking account of the helical geometry and finite-orbit-width effects. Validity of the analytical pre-dictions are verified by the Eulerian gyrokinetic code (GKV code) with very-high resolution of the phase space. The GKV simulation extended to take account of helical-ripple-trapped particles is also applied to the ITG turbu-lence in helical systems. The ITG turbulent transport level in a model case for the inward-shifted magnetic-axis configuration with a stronger instability drive is effectively suppressed by the zonal flow, and is reduced to a level comparable to that in the less unstable case for the standard configuration with smaller side-band helical field components. 1