Scale-free vortex cascade emerging from random forcing in a strongly coupled system

We elucidate the unifying aspects of self-organized criticality (SOC) and turbulence through analysis of data from a laboratory dusty plasma monolayer. We compare analysis of experimental data with simulations of a twodimensional (2D) many-body system, of 2D chaotic fluid flow, and two different SOC-models, the Zhang and the Bak–Tang–Wiesenfeld (BTW) models, all subject to steady random forcing at small scales. The scale-free vortex cascade is apparent from structure functions as well as spatio-temporal avalanche analysis. We find similar scaling exponents for the experiment, the many-body simulation, and the fluid simulation, indicating some common dynamical features. However, the exponents of the Zhang model are different from those of the BTW model, and they are all different from those of the dust and fluid systems. Thus, we conclude that the dust monolayer dynamics can be viewed as turbulent as well as avalanching, but a fluid model is a better representation of the dust dynamics for this particular experiment than the sandpile models considered. The experiment exhibits global fluctuation statistics consistent with a recent hypothesis predicting universal non-Gaussian probability density functions, 6 Author to whom any correspondence should be addressed. New Journal of Physics 10 (2008) 093018 1367-2630/08/093018+18$30.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft 2 but the model systems yield this result only in a restricted range of forcing conditions.