1. Institut für Plasmaforschung Universität Stuttgart 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

2. 2 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

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

4. 4 Torsatron TJ-K l=1, m=6 Torsatron Large plasma radius: R 0 = 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: n e = 1∙10 17 m -3 T e = 10 eV T i < 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. 5 Diagnostics: global Reynolds stress array

6. 6 Biasing electrode

7. 7 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

8. 8 Diagnostics: global Reynolds stress array

9. 9

10. 10 Cross-correlation without biasing potential density

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

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

13. 13 Spectra

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

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

16. 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. 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. 18 Thank you for your attention