15th International Conference on Plasma Surface Interactions in Controlled Fusion Devices de 27 Abril a 3 de Maio de 2002, Gifu, Japão

	Experimental Evidence of Fluctuations and Flows near Marginal Stability and Dynamical Interplay Between Gradients and Transport in the JET Plasma Boundary Region
	C. Hidalgo, B. Gonçalves, M. A. Pedrosa, C. Silva, R. Balbín, M. Hron, A. Loarte, K. Erents, G. F. Matthews e R. Pitts
	Resumo
	The structure of the naturally occurring velocity shear layer and the dynamical coupling between gradients and transport have been investigated in the JET plasma boundary region. The naturally occurring velocity shear layer organizes itself to reach a condition in which the radial gradient in the poloidal phase velocity of fluctuations is comparable to the inverse of the correlation time of fluctuations (1/t). This result suggests that ExB sheared flows organized themselves to be close to marginal stability (i.e. ?ExB . 1/t). Experimental results show that there is a strong coupling between the Probability Density Function (PDF) of gradients and ExB turbulent transport. The size of turbulent events increases when the plasma deviates from the average gradient. The resulting radial velocity of fluctuations is of the order of 20 m/s for transport events implying a small deviation from the most probable gradient. This effective radial velocity is consistent with a diffusive modeling of the plasma boundary in JET. On the contrary, the effective radial velocity increases up to 500 m/s for transport events in which the local gradient increases significantly above the most probable gradient. These results suggest a linkbetween the size of transport events and the nature of transport (diffusive versus non-diffusive) in the plasma boundary region.