Characteristics of Intermittency and ELM Dynamics in the Edge Region of Magnetic Confinement Devices

In the approach presented here we combine theoretic aspects and experimental results in order to obtain threefold information on intermittency and edge localized mode (ELM) dynamics using: a) multifractal analysis, b) level-crossing properties of plasma density time series and c) stochastic catastrophy theory (CT). Intermittency properties of the MAST spherical tokamak (L-, Hand dithering H-mode) are considered. Multifractal (MF) analysis suggests that each magnetic confinement device has distinct MF spectral characteristics and that confinement modes (L-, Hand dithering Hmodes) exhibit distinct MF spectral features. Also, cascade processes in different tokamak devices are distinct in spite of some universal common features. In the second approach intermittency is studied by considering solely the clustering of level-crossings of turbulent signals and we show that it is related to particles clustering and possibly to accumulation of vorticity. Finally, a reliable estimate of the number of equilibrium states and transitions (bifurcations) between these states is determined. This is important for determining the L-H transition as well as for identifying zonal flow formation. In addition we show that one may infer from experimental data that the ELMs are catastrophic bifurcation events.