Large-scale fluctuation structures in plasma turbulence

The role of large-scale fluctuation structures in electrostatic drift-wave-type plasma turbulence is highlighted. In particular, well-defined laboratory experiments allow one to study the dynamics of drift wave mode structures as well as `eddies' in drift wave turbulence. In the present paper we discuss the mutual relationships between observations made in linear magnetic geometry, purely toroidal geometry and magnetic confinement. The simplest structure, a saturated, nonlinear drift mode, is the starting point for a Ruelle-Takens-Newhouse transition route to chaos and weakly developed turbulence. Both spectral and phase space analysis are applied to characterize in detail the transition scenario, which is enforced due to an increased drive by the plasma equilibrium state. In addition to direct multi-probe observation, statistical approaches are most revealing for the systematic study of the spatiotemporal dynamics in fully developed drift wave turbulence. In particular, the propagation of large-scale `eddy' structures is traced by conditional statistics methods. Finally, the control of drift wave turbulence by spatiotemporal synchronization is discussed.