Institut für PlasmaforschungUniversität Stuttgart
Long-distance correlation of fluctuationsunder strong ExB shear in TJ-K
P. Manz, M. Ramisch, U. Stroth
Institut für Plasmaforschung, Universität Stuttgart
5th Coordinated Working Group Meeting forStellarator/Heliotron Studies, July 6-8 2009
Stuttgart, 07.07.09
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Long-distance correlation of fluctuations in TJ-II
Pedrosa et al, Phys. Rev. Lett. 100, 215003 (2008)
Probes are 160° toroidally displaced
A field line passing through one probe is approximately 150° poloidally apart when reaching the toroidal position of the other probe
Long-distance correlation occur during L-H transition
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Zonal flows are long-distance correlations
Fujisawa et al, Phys. Rev. Lett. 93, 165002 (2004)
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Torsatron TJ-K
l=1, m=6 Torsatron
Large plasma radius:R0 = 0.6 m
small plasma radius:a = 0.1 m
Working gas: He
Neutral gas pressure:7 mPa
Magnetic field strength: 72 mT
Plasma heating: ECRH (2.45 GHz, 1.8 kW)
Plasma parameter:ne = 1∙1017 m-3
Te = 10 eVTi < 1 eV
Advantages of TJ-K:
- Dimensionless plasma parameters are similar to those in fusion edge plasmas
- The low temperature plasma has an excellent accessibility for probe arrays
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Diagnostics: global Reynolds stress array
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Biasing electrode
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Plasma biasing scenario
Potential profile ExB-shear
|s| >max
Density profile
enhanced
particle confinement
Ramisch et al, Plasma Phys. & Control. Fusion 49, 777 (2007)
shear flow
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Diagnostics: global Reynolds stress array
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Diagnostics: global Reynolds stress array
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Cross-correlation without biasing
potential density
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Cross-correlation with biasing (+100V)
potential density
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Cross-correlation
m=4 mode m=0 mode m=3 mode
without biasing with biasing (+100V)
zonal flow-like not zonal flow-likeManz et al Phys. Plasmas 16, 042309 (2009)
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Spectra
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Cross-coherency
Manz et al Phys. Plasmas 16, 042309 (2009)
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Zonal density (m=0)
Hasegawa-Wakatani
zonal average
Manz et al, Plasma Phys. & Control. Fusion 50, 035008 (2008)
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Origin of the coherent mode (m=3)
Similar observations inH1 heliac (Shats, PPCF 48, S17 (2006)CHS (Fujisawa, PPCF 48, S31 (2006)
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Summary
Shear flows causes a strong increase in the long-range correlation:in the potential fluctuations, zonal flow-like modes are excited
density long-distance correlation is dominated by an m=3 mode
Coherency analysis reveals the existence of m=0 density fluctuationsdue to
background profile fluctuations
zonal density
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Thank you for your attention
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