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Title: The effect of an external torque on low to high confinement transitions

The effect of an external torque on low to high confinement transitions A number of experiments have attempted, with varying degrees of success, to influence the low to high confinement mode (L--H) transition through the application of an external flow shear forcing mechanism. In order to theoretically describe this type of experiment, an external torque is included in the phase transition model of Diamond {ital et} {ital al}. [Phys. Rev. Lett. {bold 72}, 2965 (1994)] for the L--H bifurcation. These equations exhibit a bifurcation between an L-mode fixed point and an H-mode fixed point with variation of a critical parameter, corresponding to the edge gradient, across a threshold value. With the addition of the external torque [from biased limiter, probe, or radio frequency (rf) wave], the character of the transition changes in a manner analogous to the addition of an external magnetic field to a ferromagnetic material. In addition to the change in the transition dynamics, there is a marked decrease in the threshold level. In this simple model, the decrease in threshold level is proportional to the applied torque to the two-thirds power, in approximate functional agreement with that seen by some experiments. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Authors: ; ;
Publication Date:
OSTI Identifier:76482
DOE Contract Number:AC05-84OR21400
Resource Type:Journal Article
Data Type:
Resource Relation:Journal Name: Physics of Plasmas; Journal Volume: 2; Journal Issue: 8; Other Information: PBD: Aug 1995
Research Org:Oak Ridge National Laboratory
Country of Publication:United States
Language:English
Subject: 70 PLASMA PHYSICS AND FUSION; PLASMA CONFINEMENT; PHASE TRANSFORMATIONS; MAGNETIC CONFINEMENT; TURBULENCE; FLUCTUATIONS; FLOW STRESS; TORQUE