Spontaneous edge <Emphasis Type="Italic">E</Emphasis> × <Emphasis Type="Italic">B</Emphasis> sheared flow development studies in the TJ-II stellarator |
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Authors: | M A Pedrosa C Hidalgo E Calderon A Alonso R O Orozco J L De Pablos TJ-II team P Balan |
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Institution: | (1) Laboratorio Nacional de Fusion por Confinamiento Magnetico, Asociacion EURATOM-CIEMAT, 28040 Madrid, Spain;(2) Institute for Ion Physics, University of Innsbruck, Innsbruck, Austria |
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Abstract: | The influence of plasma density and edge gradients in the development of perpendicular sheared flow has been investigated
in the plasma edge region of the TJ-II stellarator. It has been experimentally observed that the generation of spontaneous
perpendicular sheared flow (i.e. the naturally occurring shear layer) requires a minimum plasma density or gradient. It has
been found that there is a coupling between the onset of sheared flow development and an increase in the level of plasma edge
turbulence; once sheared flow is fully developed the level of fluctuations and turbulent transport slightly decreases whereas
edge gradients and plasma density increase. The resulting shearing rate is close to the one required to trigger a transition
to improved confinement regimes with reduction of edge turbulence, showing that spontaneous sheared flows and fluctuations
keep themselves near marginal stability.
Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Tarragona, Spain, July 3–4, 2005. |
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Keywords: | stellarator turbulence sheared flows |
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