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Title: Shear flow generation by Reynolds stress and suppression of resistive g-modes

Abstract

Suppression of resistive g-mode turbulence by background shear flow generated from a small external flow source and amplified by the fluctuation-induced Reynolds stress is demonstrated and analyzed. The model leads to a paradigm for the low-to-high (L-H) confinement mode transition. To demonstrate the L-H transition model, single-helicity nonlinear fluid simulations using the vorticity equation for the electrostatic potential, the pressure fluctuation equation and the background poloidal flow equation are used in the sheared slab configuration. The relative efficiency of the external flow and the Reynolds stress for producing shear flow depends on the poloidal flow damping parameter {nu} which is given by neoclassical theory. For large {nu}, the external flow is a dominant contribution to the total background poloidal shear flow and its strength predicted by the neoclassical theory is not enough to suppress the turbulence significantly. In contrast, for small {nu}, we show that the fluctuations drive a Reynolds stress that becomes large and suddenly, at some critical point in time, shear flow much larger than the external flow is generated and leads to an abrupt, order unity reduction of the turbulent transport just like that of the L-H transition in tokamak experiments. It is also found that, evenmore » in the case of no external flow, the shear flow generation due to the Reynolds stress occurs through the nonlinear interaction of the resistive g-modes and reduces the transport. To supplement the numerical solutions we derive the Landau equation for the mode amplitude of the resistive g-mode taking into account the fluctuation-induced shear flow and analyze the opposite action of the Reynolds stress in the resistive g turbulence compared with the classical shear flow Kelvin-Helmholtz (K-H) driven turbulence.« less

Authors:
 [1];  [2]
  1. National Inst. for Fusion Science, Nagoya (Japan)
  2. Texas Univ., Austin, TX (United States). Inst. for Fusion Studies
Publication Date:
Research Org.:
Texas Univ., Austin, TX (United States). Inst. for Fusion Studies
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
10184529
Report Number(s):
DOE/ET/53088-617; IFSR-617
ON: DE93040911; TRN: 93:021806
DOE Contract Number:  
FG05-80ET53088
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: Aug 1993
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; TURBULENT FLOW; SHEAR PROPERTIES; REYNOLDS NUMBER; TOKAMAK DEVICES; FLUCTUATIONS; H-MODE PLASMA CONFINEMENT; PLASMA INSTABILITY; STRESSES; 700340; 700370; 700330; PLASMA WAVES, OSCILLATIONS, AND INSTABILITIES; PLASMA FLUID AND MHD PROPERTIES; PLASMA KINETICS, TRANSPORT, AND IMPURITIES

Citation Formats

Sugama, H, and Horton, W. Shear flow generation by Reynolds stress and suppression of resistive g-modes. United States: N. p., 1993. Web. doi:10.2172/10184529.
Sugama, H, & Horton, W. Shear flow generation by Reynolds stress and suppression of resistive g-modes. United States. doi:10.2172/10184529.
Sugama, H, and Horton, W. Sun . "Shear flow generation by Reynolds stress and suppression of resistive g-modes". United States. doi:10.2172/10184529. https://www.osti.gov/servlets/purl/10184529.
@article{osti_10184529,
title = {Shear flow generation by Reynolds stress and suppression of resistive g-modes},
author = {Sugama, H and Horton, W},
abstractNote = {Suppression of resistive g-mode turbulence by background shear flow generated from a small external flow source and amplified by the fluctuation-induced Reynolds stress is demonstrated and analyzed. The model leads to a paradigm for the low-to-high (L-H) confinement mode transition. To demonstrate the L-H transition model, single-helicity nonlinear fluid simulations using the vorticity equation for the electrostatic potential, the pressure fluctuation equation and the background poloidal flow equation are used in the sheared slab configuration. The relative efficiency of the external flow and the Reynolds stress for producing shear flow depends on the poloidal flow damping parameter {nu} which is given by neoclassical theory. For large {nu}, the external flow is a dominant contribution to the total background poloidal shear flow and its strength predicted by the neoclassical theory is not enough to suppress the turbulence significantly. In contrast, for small {nu}, we show that the fluctuations drive a Reynolds stress that becomes large and suddenly, at some critical point in time, shear flow much larger than the external flow is generated and leads to an abrupt, order unity reduction of the turbulent transport just like that of the L-H transition in tokamak experiments. It is also found that, even in the case of no external flow, the shear flow generation due to the Reynolds stress occurs through the nonlinear interaction of the resistive g-modes and reduces the transport. To supplement the numerical solutions we derive the Landau equation for the mode amplitude of the resistive g-mode taking into account the fluctuation-induced shear flow and analyze the opposite action of the Reynolds stress in the resistive g turbulence compared with the classical shear flow Kelvin-Helmholtz (K-H) driven turbulence.},
doi = {10.2172/10184529},
journal = {},
number = ,
volume = ,
place = {United States},
year = {1993},
month = {8}
}