Gyrokinetic simulations on zonal flow–turbulence spreading coupling

Zonal flows and turbulence spreading play important roles in magnetic fusion plasma confinement, yet their coupling mechanisms remain elusive. Using global nonlinear gyrokinetic simulations, we show that turbulence spreading transports zonal flow radially, extending into the linearly stable regions after local nonlinear saturation of turbulence. Theoretical understanding has been gained by analyzing the simulation results in the context of a momentum theorem in toroidal plasmas [Hahm et al., Phys. Plasmas 31, 032310 (2024)] which is an extension of the Charney–Drazin non-acceleration theorem [Charney and Drazin, J. Geophys. Res. 66, 83 (1961)]. It indicates a direct relation between turbulence-driven enstrophy transport and perpendicular momentum generation.