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Title: Modelling enhanced confinement in drift-wave turbulence

Here, the results of modeling studies of an enhanced confinement in the drift wave turbulent plasma of the CSDX linear device are presented. The mechanism of enhanced confinement is investigated here using a reduced 1D, time-dependent model, which illustrates the exchange of enstrophy between two disparate scale structures: the mesoscale flow and profile, and the turbulence intensity fields. Mean density, mean vorticity, and turbulent potential enstrophy are the variables for this model. Total potential enstrophy is conserved in this model. Vorticity mixing occurs on a scale length related to an effective Rhines' scale of turbulence, and shrinks as both density and vorticity gradients steepen. Numerical results obtained from solution of the model agree well with the experimental data from CSDX showing: (i) a steepening of the mean density profile, indicating a radial transport barrier formation, (ii) the development of a radially sheared azimuthal flow velocity that coincides with the density steepening and initiates a turbulence quench, and (iii) negative Reynolds work values, indicating that fluctuations drive the shear flow. These observations as the magnitude of the magnetic field B increases are recovered using purely diffusive expressions for the vorticity and density fluxes. A new dimensionless turbulence parameter RDT-defined as themore » ratio of the integrated potential enstrophy transfer from turbulence to the flow, to the integrated potential enstrophy production due to relaxation of the density gradient is introduced as a turbulence collapse indicator that detects when the enhanced confinement state is triggered« less
Authors:
 [1] ;  [1] ;  [1] ;  [1]
  1. Univ. of California, San Diego, La Jolla, CA (United States)
Publication Date:
Grant/Contract Number:
SC0008378; FG02-04ER54738
Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 6; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Research Org:
Univ. of California, San Diego, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
OSTI Identifier:
1474292
Alternate Identifier(s):
OSTI ID: 1363708

Hajjar, R. J., Diamond, P. H., Ashourvan, A., and Tynan, G. R.. Modelling enhanced confinement in drift-wave turbulence. United States: N. p., Web. doi:10.1063/1.4985323.
Hajjar, R. J., Diamond, P. H., Ashourvan, A., & Tynan, G. R.. Modelling enhanced confinement in drift-wave turbulence. United States. doi:10.1063/1.4985323.
Hajjar, R. J., Diamond, P. H., Ashourvan, A., and Tynan, G. R.. 2017. "Modelling enhanced confinement in drift-wave turbulence". United States. doi:10.1063/1.4985323. https://www.osti.gov/servlets/purl/1474292.
@article{osti_1474292,
title = {Modelling enhanced confinement in drift-wave turbulence},
author = {Hajjar, R. J. and Diamond, P. H. and Ashourvan, A. and Tynan, G. R.},
abstractNote = {Here, the results of modeling studies of an enhanced confinement in the drift wave turbulent plasma of the CSDX linear device are presented. The mechanism of enhanced confinement is investigated here using a reduced 1D, time-dependent model, which illustrates the exchange of enstrophy between two disparate scale structures: the mesoscale flow and profile, and the turbulence intensity fields. Mean density, mean vorticity, and turbulent potential enstrophy are the variables for this model. Total potential enstrophy is conserved in this model. Vorticity mixing occurs on a scale length related to an effective Rhines' scale of turbulence, and shrinks as both density and vorticity gradients steepen. Numerical results obtained from solution of the model agree well with the experimental data from CSDX showing: (i) a steepening of the mean density profile, indicating a radial transport barrier formation, (ii) the development of a radially sheared azimuthal flow velocity that coincides with the density steepening and initiates a turbulence quench, and (iii) negative Reynolds work values, indicating that fluctuations drive the shear flow. These observations as the magnitude of the magnetic field B increases are recovered using purely diffusive expressions for the vorticity and density fluxes. A new dimensionless turbulence parameter RDT-defined as the ratio of the integrated potential enstrophy transfer from turbulence to the flow, to the integrated potential enstrophy production due to relaxation of the density gradient is introduced as a turbulence collapse indicator that detects when the enhanced confinement state is triggered},
doi = {10.1063/1.4985323},
journal = {Physics of Plasmas},
number = 6,
volume = 24,
place = {United States},
year = {2017},
month = {6}
}