Nonlinear instability mechanism in 3-D collisional driftwave turbulence

Numerical simulations of 3-D collisional drift-wave turbulence reveal a behavior basically different from that found in previous 2-D studies. The linear instability saturates due to energy transfer to small kz leading to formation of convective cells. The turbulence is sustained by nonlinear transfer processes between kz=0 and kz≠0 modes, the latter acting as a catalyst. The system tends to relax to a nonturbulent poloidal shear flow. Introducing a damping of this flow gives rise to an intermittent behavior, where laminar periods of zero flux alternate with bursts of turbulence and large flux, the transitions occuring on time scale short compared with the linear growth times. (orig.)