About bursty behaviour, coherent structures, wide scrape-off layer and large parallel flows in the edge of the Tore Supra tokamak |
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Authors: | I Nanobashvili J P Gunn P Devynck G Ciraolo Ph Ghendrih Y Sarazin |
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Institution: | (1) Association EURATOM-CEA, CEA/DSM/DRFC, CEA Cadarache, 13108 Saint Paul Lez Durance, France;(2) Present address: Andronikashvili Institute of Physics and Kharadze Abastumani Astrophysical Observatory, Tbilisi, Georgia |
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Abstract: | We present the measurements of plasma characteristics in the scrape-off layer (SOL) of the Tore Supra tokamak performed by
means of reciprocating Langmuir probe. The probe is inserted into the machine from top. As the radial distance from last closed
flux surface (LCFS) increases, ion saturation current exhibits stronger bursty character and its probability density function
becomes increasingly skewed towards positive values. At the same time, burst duration and inter-burst time increase dramatically.
We explain this phenomenon by radial propagation and dynamics of the ensemble of coherent turbulent structures of different
size. The results of two-dimensional fluid modelling based of flux-driven interchange instability mechanism are in excellent
agreement with experimental results.
We obtained clear experimental evidence that most of the coherent structures are formed in poloidally localized region of
the SOL around the outboard midplane. If the probe is magnetically connected to this region, the SOL is very wide and we detect
bursty behaviour in the far SOL. On the other hand, if the probe is not magnetically connected to the outboard midplane region
(magnetic field lines are intercepted by the outboard limiter), then the SOL is very thin and bursty behaviour is much less
prominent. Detection of bursty behaviour in the far SOL is correlated with existence of wide SOL pointing on important role
of bursty transport by means of coherent turbulent structures in establishing the width of the SOL in tokamaks.
The measurements of parallel flow in the SOL shows that plasma particle radial flux coming from confinement region to the
SOL is mostly poloidally localized around the outboard midplane. Our estimations show that more than 80% of plasma particle
radial flux is coming from confinement region to the SOL in poloidally localized region — approximately ±15° — around the
outboard midplane.
Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Roma, Italy, June 26–27, 2006. |
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Keywords: | 52 35 Ra 52 25 Fi 52 25 Gj 47 27 De 47 27 E- |
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