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Schlagwörter:
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Zusammenfassung:
The intermittent turbulent transport in the scrape-off-layer (SOL) of Alcator C-Mod [I.H. Hutchinson, R. Boivin, P.T. Bonoli et
al., Nucl. Fusion 41, 1391 (2001)] is studied experimentally by imaging with a very high density of spatial measurements. The
two-dimensional structure and dynamics of emission from a localized gas puff are observed, and intermittent features (also
sometimes called "filaments" or "blobs") are typically seen. The characteristics of the spatial structure of the turbulence and their
relationship to the time-averaged SOL profiles are discussed and compared with those measured on the National Spherical
Torus Experiment [M. Ono, S. M. Kaye, Y.-K. M. Pong et al., Nucl. Fusion 40, 557 (2000)]. The experimental observations
are compared also with three-dimensional nonlinear numerical simulations of edge turbulence. Radial profiles of the poloidal
wave number spectra and the poloidal scale length from the simulations are in reasonable agreement with those obtained from the
experimental images, once the response of the optical system is accounted for. The resistive ballooning mode is the dominant
linear instability in the simulations. The ballooning character of the turbulence is also consistent with fluctuation measurements
made at the inboard and outboard midplane, where normalized fluctuation levels are found to be about 10 times smaller on the
inboard side. For discharges near the density limit, turbulent structures are seen on closed flux surfaces.
