In-out asymmetry of zonal flow shear and turbulence reduction

In-out asymmetry of ion temperature gradient turbulence in toroidal geometry is studied by performing nonlinear gyrokinetic simulation using the GyroKinetic Plasma Simulation Program code [Kwon et al., Nucl. Fusion 52, 013004 (2012)]. Effects of self-generated zonal flow shear on the in-out asymmetry of radial correlation length and amplitude of turbulence are addressed by varying collisionality. Both quantities exhibit strong in-out asymmetry (longer and higher, respectively, at the low field side) in the absence of zonal flows. When the zonal flow shear (which is higher at the low field side) gets stronger, the radial correlation length decreases with its in-out asymmetry also getting reduced as expected from E × B shear decorrelation theory. On the other hand, in-out asymmetry of turbulence amplitude behaves differently from that of the radial correlation length.