Flow and shear behavior in the edge and scrape-off layer of L-mode plasmas in National Spherical Torus Experiment

Journal Article · Sat Jan 15 00:00:00 EST 2011 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.3533435· OSTI ID:21532173

Sechrest, Y; Munsat, T ^[1]; D'Ippolito, D A; Myra, J R; Russell, D ^[2]; Maqueda, R J; Zweben, S J ^[3]

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1. Department of Physics, University of Colorado, Boulder, Colorado 80309 (United States)
2. Lodestar Research Corporation, Boulder, Colorado 80301 (United States)
3. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540 (United States)

Fluctuations in the edge and scrape-off layer (SOL) of L-mode plasmas in the National Spherical Torus Experiment [Kaye et al., Phys. Plasmas 8, 1977 (2001)] as observed by the gas puff imaging (GPI) diagnostic are studied. Calculation of local, time resolved velocity maps using the hybrid optical flow and pattern matching velocimetry code enables analysis of turbulent flow and shear behavior. Periodic reversals in the direction of the poloidal flow near the separatrix are observed. Also, poloidal velocities and their radial shearing rate are found to be well correlated with the fraction of D{sub {alpha}} light contained in the SOL, which acts as a measure of turbulent bursts. The spectra of GPI intensity and poloidal velocity both have a strong feature near 3 kHz, which appears to correspond with turbulent bursts. This mode exhibits a poloidal structure with poloidal wavenumber of 7.7 m{sup -1} for GPI intensity and 3.4 m{sup -1} for poloidal velocity, and the poloidal velocity fluctuations near 3 kHz remain coherent over length scales in excess of the turbulent scales. Furthermore, recent SOL turbulence simulations find a parameter regime that exhibits periodic bursty transport and shares many qualitative similarities with the experimental data. Strong correlations between the shearing rate and the turbulent bursts are observed for time periods of {approx}2 ms, but the relationship is complicated by several factors. Finally, measurements of the radial profiles of the Reynolds shear stresses are reported. These radial profiles exhibit many similarities for several shots, and a region with positive radial gradient is seen to be coincident with local flow shear.

• OSTI ID: 21532173
• Journal Information: Physics of Plasmas, Vol. 18, Issue 1; Other Information: DOI: 10.1063/1.3533435; (c) 2011 American Institute of Physics; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
CORRELATIONS
FLUCTUATIONS
L-MODE PLASMA CONFINEMENT
MAGNETOHYDRODYNAMICS
NSTX DEVICE
PLASMA DIAGNOSTICS
PLASMA SCRAPE-OFF LAYER
PLASMA SIMULATION
SHEAR
TURBULENCE
BOUNDARY LAYERS
CLOSED PLASMA DEVICES
CONFINEMENT
FLUID MECHANICS
HYDRODYNAMICS
LAYERS
MAGNETIC CONFINEMENT
MECHANICS
PLASMA CONFINEMENT
SIMULATION
SPHEROMAK DEVICES
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
VARIATIONS