Shear flow generation by Reynolds stress and suppression of resistive gmodes
Abstract
Suppression of resistive gmode turbulence by background shear flow generated from a small external flow source and amplified by the fluctuationinduced Reynolds stress is demonstrated and analyzed. The model leads to a paradigm for the lowtohigh (LH) confinement mode transition. To demonstrate the LH transition model, singlehelicity 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 LH transition in tokamak experiments. It is also found that, evenmore »
 Authors:

 National Inst. for Fusion Science, Nagoya (Japan)
 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/53088617; IFSR617
ON: DE93040911; TRN: 93:021806
 DOE Contract Number:
 FG0580ET53088
 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; HMODE 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 gmodes. United States: N. p., 1993.
Web. doi:10.2172/10184529.
Sugama, H, & Horton, W. Shear flow generation by Reynolds stress and suppression of resistive gmodes. United States. doi:10.2172/10184529.
Sugama, H, and Horton, W. Sun .
"Shear flow generation by Reynolds stress and suppression of resistive gmodes". 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 gmodes},
author = {Sugama, H and Horton, W},
abstractNote = {Suppression of resistive gmode turbulence by background shear flow generated from a small external flow source and amplified by the fluctuationinduced Reynolds stress is demonstrated and analyzed. The model leads to a paradigm for the lowtohigh (LH) confinement mode transition. To demonstrate the LH transition model, singlehelicity 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 LH 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 gmodes and reduces the transport. To supplement the numerical solutions we derive the Landau equation for the mode amplitude of the resistive gmode taking into account the fluctuationinduced shear flow and analyze the opposite action of the Reynolds stress in the resistive g turbulence compared with the classical shear flow KelvinHelmholtz (KH) driven turbulence.},
doi = {10.2172/10184529},
journal = {},
number = ,
volume = ,
place = {United States},
year = {1993},
month = {8}
}