The effect of an external torque on low to high confinement transitions
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-8070 (United States)
- University of California at San Diego, La Jolla, California 92093-0319 (United States)
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}.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 76482
- Journal Information:
- Physics of Plasmas, Vol. 2, Issue 8; Other Information: PBD: Aug 1995
- Country of Publication:
- United States
- Language:
- English
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