Investigation of intermittency and generalized self-similarity of turbulent boundary layers in laboratory and magnetospheric plasmas: towards a quantitative definition of plasma transport features

A comparative analysis of the fundamental properties of fluctuations in the vicinity of boundaries in fusion plasmas and in plasmas of magnetospheric turbulent boundary layers (TBLs) shows the similarity of their basic statistical characteristics, including the scaling of the structure functions and mutifractal parameters. Important features observed include intermittent fluctuations and anomalous mass and momentum transport, due to sporadic plasma flow injections with large flow amplitudes occuring with a much higher probability than predicted for classical Gaussian diffusion. Turbulence in edge fusion plasmas and in TBLs exhibits general self-similarity in a wide range of scales extending to the dissipation scale. Experimental scalings obtained for plasma TBLs are compared with neutral fluid results, revealing the universal properties of developed turbulence. TBL scalings are described within the log-Poisson model, which takes quasi-one-dimensional dissipative structures into account. The time ($\tau$) dependence of the mean-square displacement $\langle \delta x^2 \rangle$ obtained from the experimental parameters of the log-Poisson distribution takes the form $\langle \delta x^2 \rangle \varpropto \tau^\alpha$ with $\alpha \approx$ 1.2 – 1.8 and indicates the presence of superdiffusion in the TBLs studied. Determining the nature of the generalized diffusion process from available regular data is a necessary step toward the quantitative description of TBL transport.