Nonlinear Dynamics of Magnetic Electron Drift Modes and Self-Organization Phenomena in Turbulent Plasma

摘要

It is already well accepted, that nonlinear interaction of short-scale fluctuations in magnetized plasma can generate low-frequency, large-scale nonlinear structures (so called zonal flows and streamers) that play an important role, for example, in controlling plasma transport properties in magnetic confinement systems. Here we investigate the generation of large-scale magnetic structures in magnetic electron drift mode (MEDM) turbulence. These modes are of interest in, e.g.,laser fusion experiments, where they are thought to be responsible for the very strong self-generated magnetic fields which have been observed since the early 1970s. The driving mechanism is the baroclinic effect, i.e.,the fluctuating electron temperature and density gradients should align. To understand nonlinear dynamics of these modes we employ the ansatz of scale separation to distinguish between the small-scale fluctuations of magnetic electron drift modes and the large-scale shear flow pattern generated by turbulence. Then, the evolution equations for mean flow generation are obtained by averaging the model equations for magnetic electron drift modes over fast small-scales. When the large-scale structures are excited, they form an environment for the parent drift waves. The propagation of drift modes in such weakly inhomogeneous media with slowly varying parameters can be conveniently described with the help of a wave kinetic equation for the wave action density in r-k space. The sources of these slow spatial and temporal variations are flow induced velocity perturbations. Finally, the evolution of nonlinearly interacting MEDM is illustrated by a simulation study of the model equations for the different set of parameters.