Long-distance coupling between edge parameters' fluctuations has been investigated in the TJ-II stellarator. Results show long-range correlations in potential fluctuations, which are amplified by the development of radial electric fields during transitions to improved-confinement regimes, whereas there is no correlation between ion saturation current signals. These experimental findings suggest the importance of long-range correlations as a new fingerprint of the plasma behavior during the development of edge shear flows and the key role of electric fields to amplify them.
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Evidence of long-distance correlation of fluctuations during edge transitions to improved-confinement regimes in the TJ-II stellarator.
Phys Rev Lett
May 2008
Laboratorio Nacional de Fusión, Asociación EURATOM-CIEMAT, 28040-Madrid, Spain.
Long-distance coupling between edge parameters' fluctuations has been investigated in the TJ-II stellarator. Results show long-range correlations in potential fluctuations, which are amplified by the development of radial electric fields during transitions to improved-confinement regimes, whereas there is no correlation between ion saturation current signals. These experimental findings suggest the importance of long-range correlations as a new fingerprint of the plasma behavior during the development of edge shear flows and the key role of electric fields to amplify them.
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Phys Rev Lett
November 2006
Centro Atómico Bariloche (CNEA) and Instituto Balseiro, Bariloche, Argentina.
A consistent description of transitions to improved confinement regimes in terms of a probabilistic transport model is presented. The model has two thresholdlike mechanisms, acting, respectively, on the first and second spatial derivatives of the density. These mechanisms allow switching between three different transport channels: one corresponding to classical diffusion and the other two to different scale-free transport mechanisms.
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Phys Rev Lett
May 2005
National Institute for Fusion Science, Toki, Gifu, Japan.
Two-dimensional structures of the electrostatic potential, density, and flow velocity near the edge of a tokamak plasma are investigated. The model includes the nonlinearity in bulk-ion viscosity and turbulence-driven shear viscosity. For the case with the strong radial electric field (H mode), a two-dimensional structure in a transport barrier is obtained, giving a poloidal shock with a solitary radial electric field profile.
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Phys Rev E Stat Nonlin Soft Matter Phys
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Laboratorio Nacional de Fusion, Euratom-Ciemat, 28040 Madrid, Spain.
The link between the development of sheared flows and the structure of turbulence has been investigated in the plasma boundary region of the TJ-II stellarator. The development of the naturally occurring velocity shear layer requires a minimum plasma density. Near this critical density, the level of edge turbulent transport and the turbulent kinetic energy significantly increases in the plasma edge.
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Phys Rev Lett
September 2001
Mechanical and Aerospace Engineering Department, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA.
The nonlinear coupling between small scale high-frequency turbulence and larger scale lower-frequency fluctuations increases transiently in transitions to improved confinement in the DIII-D tokamak. This increase starts before the rapid turbulence suppression and E x B shear-flow development in the region that becomes the H-mode transport barrier/shear flow region. After the transition, the coupling returns to L-mode levels.
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