Self-consistent 2D model for L-H transitions in tokamaks

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:489541

Guzdar, P N; Hassam, A B ^[1]

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1. Univ. of Maryland, College Park, MD (United States)

A two-dimensional self-consistent model for L-H transitions in tokamaks has been developed. A set of {open_quote}fast{close_quote} equations for the density and vorticity of resistive ballooning modes, and {open_quote}slow{close_quote} equations for the equilibrium density, vorticity and the parallel momentum have been derived for a toroidal plasma, and have been solved numerically. The L-mode phase consists of strong poloidally asymmetric particle transport driven by resistive ballooning modes with a single toroidal mode number with larger flux on the outboard side compared to the inboard side. As a consequence the density is more flattened on the outside of the tokamak compared to the inside and is no longer constant on a flux surface. With the onset of shear flow driven by a combination of toroidal drive mechanisms as well as the Reynold`s Stress, the fluctuations associated with the resistive ballooning modes are attenuated which leads to a strong reduction in the particle transport. The drop in the particle transport results in steepening of the density profile. The time development of the fluctuations shows that the fluctuations on the outside are the first to be reduced in amplitude during the build-up of the shear flow. The fluctuations on the inside first increase in amplitude during the transition, followed by a reduction. The fluctuations in the H-mode phase axe poloidally localized at the top/bottom. The strong radial localization of these secondary modes does not degrade the particle transport and the H-mode is sustained in the late phase by the toroidal drive.

• OSTI ID: 489541
• Report Number(s): CONF-960354--
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BALLOONING INSTABILITY
H-MODE PLASMA CONFINEMENT
PLASMA SIMULATION
TOKAMAK DEVICES