Physical mechanism of enhanced stability from negative shear in tokamaks: Implications for edge transport and the L-H transition

Journal Article · Sat Jun 01 04:00:00 EDT 1996 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.871928· OSTI ID:284283

Antonsen, Jr, T M; Drake, J F; Guzdar, P N; Hassam, A B; Lau, Y T; Liu, C S; Novakovskii, S V ^[1]

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1. Institute for Plasma Research, University of Maryland, College Park, Maryland 20742 (United States)

The enhancement of stability to ballooning modes from negative shear in tokamaks is shown to be a simple consequence of the orientation of the convective cell with respect to the toroidally outward effective gravity, {ital g}{searrow}. For modest positive shear, convective cells remain oriented along {ital g}{searrow} as they map along field lines. In contrast, for negative shear or very positive shear convective cells twist strongly away from {ital g}{searrow} and are less strongly driven. The twist of convection cells is controlled by the profile of the vertical magnetic field along the outer midplane, {ital B}{sub {ital z}}. Twist is a minimum in regions where {ital B}{sub {ital z}} is independent of the major radius. Transport should be highest in such locations. Resistive ballooning modes in the tokamak edge are strongly stabilized by modest values of negative shear. Tokamak discharges with finite values of {beta}{sub {ital p}} develop regions of local negative shear on the outside midplane of the plasma torus. This local negative shear should self-stabilize resistive ballooning modes at finite values of the poloidal beta. This effect may impact the transition to high confinement operation (H-mode). {copyright} {ital 1996 American Institute of Physics.}

• OSTI ID: 284283
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 6 Vol. 3; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BALLOONING INSTABILITY
H-MODE PLASMA CONFINEMENT
MAGNETIC SURFACES
SHEAR
TFTR TOKAMAK
TOA
TOKAMAK DEVICES