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Long-distance correlation of fluctuations under strong ExB shear in TJ-K

Long-distance correlation of fluctuations under strong ExB shear in TJ-K. P. Manz, M. Ramisch, U. Stroth Institut für Plasmaforschung, Universität Stuttgart 5th Coordinated Working Group Meeting for Stellarator/Heliotron Studies, July 6-8 2009 Stuttgart, 07.07.09.

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Long-distance correlation of fluctuations under strong ExB shear in TJ-K

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  1. 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 for Stellarator/Heliotron Studies, July 6-8 2009 Stuttgart, 07.07.09

  2. Long-distance correlation of fluctuations in TJ-II 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 Pedrosa et al, Phys. Rev. Lett. 100, 215003 (2008)

  3. Zonal flows are long-distance correlations Fujisawa et al, Phys. Rev. Lett. 93, 165002 (2004)

  4. 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 eV • Ti < 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

  5. Diagnostics: global Reynolds stress array

  6. Biasing electrode

  7. Plasma biasing scenario Density profile Potential profile ExB-shear enhanced particle confinement • shear flow |s| >max Ramisch et al, Plasma Phys. & Control. Fusion 49, 777 (2007)

  8. Diagnostics: global Reynolds stress array

  9. Diagnostics: global Reynolds stress array

  10. Cross-correlation without biasing density potential

  11. Cross-correlation with biasing (+100V) density potential

  12. Cross-correlation with biasing (+100V) without biasing m=4 mode m=3 mode m=0 mode not zonal flow-like zonal flow-like Manz et al Phys. Plasmas 16, 042309 (2009)

  13. Spectra

  14. Cross-coherency Manz et al Phys. Plasmas 16, 042309 (2009)

  15. Zonal density (m=0) Hasegawa-Wakatani zonal average Manz et al, Plasma Phys. & Control. Fusion 50, 035008 (2008)

  16. Origin of the coherent mode (m=3) Similar observations in H1 heliac (Shats, PPCF 48, S17 (2006) CHS (Fujisawa, PPCF 48, S31 (2006)

  17. 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 fluctuations • due to • background profile fluctuations • zonal density

  18. Thank you for your attention

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