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Title: Dynamics of zonal shear collapse with hydrodynamic electrons

Abstract

This paper introduces a theory for the collapse of the edge zonal shear layer, as observed at the density limit at low β. We investigate the scaling of the transport and mean profiles with the adiabaticity parameter α, with special emphasizes on fluxes relevant to zonal flow (ZF) generation. We show that the adiabaticity parameter characterizes the strength of production of zonal flows and so determines the state of turbulence. A 1D reduced model that self-consistently describes the spatiotemporal evolution of the mean density $$\overline{n}$$, the azimuthal flow $$\overline{v}_{y}$$, and the turbulent potential enstrophy ε=$$\langle$$ñ–∇ 2$$\tilde{\phi}$$) 2/2$$\rangle$$—related to fluctuation intensity—is presented. Quasi-linear analysis determines how the particle flux Γ n and vorticity flux Π=–χ y2v yres scale with α, in both hydrodynamic and adiabatic regimes. As the plasma response passes from adiabatic (α>1) to hydrodynamic (α<1), the particle flux Γ n is enhanced and the turbulent viscosity χ y increases. However, the residual flux Π res—which drives the flow—drops with α. As a result, the mean vorticity gradient ∇ 2$$\overline{v}$$ yresy—representative of the strength of the shear—also drops. The shear layer then collapses and turbulence is enhanced. The collapse is due to a decrease in ZF production, not an increase in damping. A physical picture for the onset of collapse is presented. The findings of this paper are used to motivate an explanation of the phenomenology of low β density limit evolution. A change from adiabatic (α=k$$^{2}_{z}$$v$$^{2}_{th}$$/(||ω||ν ei)>1) to hydrodynamic (α<1) electron dynamics is associated with the density limit.

Authors:
 [1];  [2]; ORCiD logo [3]
  1. Univ. of California, San Diego, CA (United States)
  2. Univ. of California, San Diego, CA (United States); Southwestern Inst. of Physics, Chengdu (China)
  3. Center for Astrophysics and Space Sciences, University of California San Diego, La Jolla, California 92093, USA; Department of Physics, University of California, San Diego, California 92093, USA
Publication Date:
Research Org.:
Univ. of California, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1540209
Alternate Identifier(s):
OSTI ID: 1441086
Grant/Contract Number:  
FG02-04ER54738
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 6; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English

Citation Formats

Hajjar, R. J., Diamond, P. H., and Malkov, M. A. Dynamics of zonal shear collapse with hydrodynamic electrons. United States: N. p., 2018. Web. doi:10.1063/1.5030345.
Hajjar, R. J., Diamond, P. H., & Malkov, M. A. Dynamics of zonal shear collapse with hydrodynamic electrons. United States. doi:10.1063/1.5030345.
Hajjar, R. J., Diamond, P. H., and Malkov, M. A. Fri . "Dynamics of zonal shear collapse with hydrodynamic electrons". United States. doi:10.1063/1.5030345. https://www.osti.gov/servlets/purl/1540209.
@article{osti_1540209,
title = {Dynamics of zonal shear collapse with hydrodynamic electrons},
author = {Hajjar, R. J. and Diamond, P. H. and Malkov, M. A.},
abstractNote = {This paper introduces a theory for the collapse of the edge zonal shear layer, as observed at the density limit at low β. We investigate the scaling of the transport and mean profiles with the adiabaticity parameter α, with special emphasizes on fluxes relevant to zonal flow (ZF) generation. We show that the adiabaticity parameter characterizes the strength of production of zonal flows and so determines the state of turbulence. A 1D reduced model that self-consistently describes the spatiotemporal evolution of the mean density $\overline{n}$, the azimuthal flow $\overline{v}_{y}$, and the turbulent potential enstrophy ε=$\langle$ñ–∇2$\tilde{\phi}$)2/2$\rangle$—related to fluctuation intensity—is presented. Quasi-linear analysis determines how the particle flux Γn and vorticity flux Π=–χy∇2vy+Πres scale with α, in both hydrodynamic and adiabatic regimes. As the plasma response passes from adiabatic (α>1) to hydrodynamic (α<1), the particle flux Γn is enhanced and the turbulent viscosity χy increases. However, the residual flux Πres—which drives the flow—drops with α. As a result, the mean vorticity gradient ∇2$\overline{v}$y=Πres/χy—representative of the strength of the shear—also drops. The shear layer then collapses and turbulence is enhanced. The collapse is due to a decrease in ZF production, not an increase in damping. A physical picture for the onset of collapse is presented. The findings of this paper are used to motivate an explanation of the phenomenology of low β density limit evolution. A change from adiabatic (α=k$^{2}_{z}$v$^{2}_{th}$/(||ω||νei)>1) to hydrodynamic (α<1) electron dynamics is associated with the density limit.},
doi = {10.1063/1.5030345},
journal = {Physics of Plasmas},
number = 6,
volume = 25,
place = {United States},
year = {2018},
month = {6}
}

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