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

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

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 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

5

Diagnostics: global Reynolds stress array

6

Biasing electrode

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

Diagnostics: global Reynolds stress array

9

Diagnostics: global Reynolds stress array

10

Cross-correlation without biasing

potential density

11

Cross-correlation with biasing (+100V)

potential density

12

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)

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 inH1 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 fluctuationsdue to

background profile fluctuations

zonal density

18

Thank you for your attention