On the scaling of avaloids and turbulence with the average density approaching the density limit

Journal Article · Mon Aug 15 04:00:00 EDT 2005 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.1953592· OSTI ID:20764463

Antar, G Y; Counsell, G; Ahn, J -W ^[1]

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1. University of California San Diego, 9500 Gilman Dr., La Jolla, California 92093-0417 (United States)

This article is dedicated to the characterization of turbulent transport in the scrape-off layer of the Mega Ampere Spherical Tokamak [A. Sykes et al., Phys. Plasmas 8, 2101 (2001)] as a function of the average density (n{sub L}). The aim is to answer a renewed interest in this subject since the bursty character of turbulence in the scrape-off layer was shown to be caused by large-scale events with high radial velocity reaching about 1/10th of the sound speed called avaloids [G. Antar et al., Phys. Rev. Lett 87, 065001 (2001)]. With increasing density, turbulence and transport increase nonlinearly at the midplane while remaining almost unchanged in the target region. Using various and complementary statistical analyses, the existence of a 'critical' density, at n{sub L}/n{sub G}{approx_equal}0.35 is emphasized; n{sub G} is the Greenwald density. Both above and below this density, intermittency decreases and avaloids play a decreasing role in the particle radial transport. This is interpreted as caused by the interplay between avaloids and the surrounding turbulent structures which mix them more efficiently with increasing density as the level of the background turbulence increases. The scaling of the different quantities with respect to the normalized density is obtained. It reveals that not only the level of turbulence and transport increase, but also the radial velocity and length scales. This increases the coupling between the hot plasma edge and the cold scrape-off layer that may explain the disruptive instability occurring at high densities.

• OSTI ID: 20764463
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 8 Vol. 12; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
CHARGED-PARTICLE TRANSPORT
COUPLING
HOT PLASMA
NONLINEAR PROBLEMS
PLASMA CONFINEMENT
PLASMA DENSITY
PLASMA INSTABILITY
PLASMA SCRAPE-OFF LAYER
RADIAL VELOCITY
SOUND WAVES
SPHERICAL CONFIGURATION
TOKAMAK DEVICES
TURBULENCE