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P: Fachverband Plasmaphysik
P 16: Poster: Magnetischer Einschluss
P 16.14: Poster
Wednesday, April 1, 2009, 17:30–19:30, Foyer des IfP
Comparison of turbulent scrape-off layer fluctuations between the outer midplane and close to the X-point in Alcator C-Mod — •Olaf Grulke1, James L. Terry2, and Stewart J. Zweben3 — 1MPI for Plasma Physics, EURATOM Association, Greifswald — 2MIT-PSFC, Cambridge, USA — 3PPPL, Princeton, USA
Turbulent fluctuations in the tokamak scrape-off layer (SOL) generally display an intermittent character with strongly non-Gaussian amplitude statistics. Spatiotemporal imaging of turbulent fluctuations at the outer midplane revealed the propagation of turbulent field-aligned filament structures, which peel-off the separatrix region and propagate radially outwards to the wall A newly installed D_alpha turbulent imaging diagnostic measuring in the strong magnetic shear region close to the lower X-point in Alcator C-Mod allows for a detailed comparison of the properties of turbulent fluctations between the outer midplane and X-point region. In contrast to the mostly circular cross-sections of turbulent structures at the midplane, structures are strongly elongated in radial direction at the X-point view. The elongation is consistent with magnetic flux surface expansion, which strongly suggests the filamentary nature of structures along the magnetic field. The X-point imaging data are directly compared to simultaneous fluctuation measurements obtained from an array of D_alpha diode views arranged radially and poloidally at the outer midplane. The statistical properties of fluctuations and the propagation speed of spatiotemporal fluctuations structures in the two regions are compared.