Observation of self-binding turbulent fluctuations in simulation plasma and their relevance to plasma kinetic theories

Non-wave-like fluctuations of the phase-space density are observed in simulations of turbulent plasma. During decay from an initial state, the mean square fluctuation level decays at a much slower rate than that of an individual fluctuation. The distribution function of the fluctuation amplitudes becomes non-Gaussian (skewed) in favor of negative fluctuations. An enhancement in the aggregate fluctuation lifetime is also observed when the turbulence is driven by an external source. A model based on a collection of self-binding negative fluctuations, called phase-space density holes, can explain the observations. Collisions between holes produce hole fragments and lead to fluctuation decay. However, the hole fragments are self-binding and tend to recombine into new holes. The implications of these results for kinetic theories of plasma turbulence are discussed. In particular, it is shown that the theory of clumps, when suitably modified to include fluctuation self-binding, can explain many features of the nonlinear instability recently observed in computer simulations.