Intermittency and extended self-similarity in space and fusion plasma: boundary effects

Abstract

A comparative study of fluctuation features in the edge plasma of fusion devices and in turbulent boundary layers (TBLs) of the Earth's magnetosphere has demonstrated similar statistical characteristics including scalings of structure functions and multifractal spectra. The detected intermittency and anomalous transport of mass and momentum is carried by sporadic plasma flux bursts with nonGaussian probability of flux magnitude. The turbulence exhibits a generalized (extended) self-similarity in an extended scale range. The experimental scalings of the structure functions are rather well fitted by the log-Poisson model considering quasi-1D singular dissipative structures. It appears that the turbulence in the edge plasma of fusion devices and in the TBL of the Earth's magnetosphere is governed by cross-field motions similar to hydrodynamic turbulence. Here the experimental scalings from the plasma are available for a comparison with experimental results from neutral fluids. The plasma scalings display universal properties of intermittent turbulence. A statistical approach permits us to evaluate turbulent transport scalings. The time dependence of an average squared particle displacements ⟨δx2⟩ ∝ τα infers superdiffusion with α ≈ 1.4–1.87 > 1.