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This paper analyses the main characteristics of turbulent transport models in the case where the flux is fixed and the mean profile is allowed to fluctuate. These models include two dimensional models for ion temperature gradient in the core and interchange in the scrape off layer, and a three dimensional model for resistive ballooning in the core. Turbulent transport exhibits some features of self-organized critical models. Indeed, the radial flux consists in intermittent ballistic bursts, called avalanches. Inward ballistic events are also observed. The frequency spectrum of the flux exhibits a structure similar to the one of a sand pile automaton, including a 1/f decrease. The departure from a Gaussian of the probability density function of the gradient depends on the radial position and on the mode. In the case of a peaked source, the equilibrium profiles are found to be super-critical, i.e. stay above the critical gradient. Finally the effective turbulent diffusivity differs significantly from the one computed at fixed gradient, with the same average gradient.

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Bibliographic Reference: Article: International School of Physics, (1998)
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