Berlin 2005 – wissenschaftliches Programm

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P: Plasmaphysik

P 16: Magnetischer Einschluß 1

P 16.1: Fachvortrag

Montag, 7. März 2005, 11:00–11:30, HU 3038

Spatiotemporal fluctuation structures and intermittent transport in the scrape-off layer of Alcator C-Mod — •Olaf Grulke — MPI für Plasmaphysik, EURATOM Assoziation, 17491 Greifswald

Experimental observations and nonlinear numerical simulations indicate that a major contribution to the cross-field transport in the scrape-off layer (SOL) is caused by intermittent events. These events are related to fluctuation structures, called ’blobs’, ’avaloids’, ’intermittent plasma objects’, which form and propagate coherently radially into the SOL. Such intermittent transport events are not only important for confinement properties of fusion devices but have also a strong impact on divertor heat loads and wall recycling phenomena. Investigations on the dynamics of turbulent SOL fluctuations using turbulence imaging in Alcator C-Mod is presented. The main diagnostic tools for the characterization of blobs are a fast camera (frame-rate 250kHz) recording Dα light fluctuations and a radial array of fast Dα diodes. The field of view covers the SOL and edge plasma at the outer midplane (8×8cm). It shows that blobs form close to the separatrix in the high pressure gradient region and propagate into the SOL, thereby causing radial correlation lengths longer than the blob size. The optical measurement in combination with Langmuir probe measurements shows that the radial propagation is a result of the self-consistent dipole-like plasma potential structure associated with the blobs. Radial correlations are not only found to be limited to the scrape-off layer but extend across the separatrix into the edge plasma showing the close interplay between the edge and SOL plasma.
O. E. Garcia et al., Phys. Rev. Letters 92(16), 2004