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HT-7

HT-7. ASIPP. Turbulence and coherent structures in the HT-7 Tokamak. Guo Sheng Xu ( 徐国盛 ) B.N. Wan, W. Zhang, S.Y. Ding, J.F. Chang, Y.D. Li Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China gsxu@ipp.ac.cn Hang Zhou meeting Sept. 25, 2007. Plasma edge region:

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HT-7

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  1. HT-7 ASIPP Turbulence and coherent structures in the HT-7 Tokamak Guo Sheng Xu (徐国盛) B.N. Wan, W. Zhang, S.Y. Ding, J.F. Chang, Y.D. Li Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China gsxu@ipp.ac.cn Hang Zhou meeting Sept. 25, 2007

  2. Plasma edge region: Langmuir probe arrays systems

  3. Questions presented for discussion • Evidence for ballooning structures of plasma turbulence in HT-7 • Zonal flows measurements in HT-7 • Electrostatic coherent mode in HT-7 • Multi-scale coherent structure in plasma turbulence • Open questions

  4. 实验中测量到的湍流，显然是充分发展的非线性饱和状态的结果。我们看到的不是一个线性的单模，而是多模叠加并充分演化的最终状态。非线性湍流模拟提供了一个和实验比较以及理解实验结果的平台。实验中测量到的湍流，显然是充分发展的非线性饱和状态的结果。我们看到的不是一个线性的单模，而是多模叠加并充分演化的最终状态。非线性湍流模拟提供了一个和实验比较以及理解实验结果的平台。 Zonal flows break the global eigenmode structure in ITG turbulence  more isotropic in  direction toroidal linear mode coupling Ballooning structures

  5. In a torus linear mode couplingballooning structures Toroidal global eigenmode single mode structure k kr

  6. At plasma edge turbulence propagate in the electron diamagnetic direction and also propagate in the radial direction

  7. r

  8. A movie shows the intermittently occurring coherent structure in HT-7

  9. r

  10. r

  11. HT-7上发现湍流的实频依赖于当地参数。 Turbulence frequency was found increase with Te Propagate in the electron diamagnetic direction In plasma core measured by CO2 collective scattering In plasma edge measured by Langmuir probe ks = 1 ~ 5 ks = 0 ~ 1 In plasma core frequency band 10 kHz ~ 1 MHz /ci = 0 ~ 6% In plasma edge frequency band 10 kHz ~ 300 kHz /ci = 0 ~ 2%

  12. In plasma edge measured by Langmuir probe ne0 ~ 1.51019m-3

  13. Questions presented for discussion • Evidence for ballooning structures of plasma turbulence in HT-7 • Zonal flows measurements in HT-7 • Electrostatic coherent mode in HT-7 • Multi-scale coherent structure in plasma turbulence • Open questions

  14. ks = 0 ~ 1 /ci = 0 ~ 2% Zonal flows spectrum • There are generally three components in the measured fluctuation spectra: • broad band turbulence • zero-mean-frequency zonal flows • low frequency coherent mode

  15. HT-7 ASIPP Zero-mean-frequency zonal-flow mode Study on the HT-7 tokamak Zonal flows pattern

  16. HT-7 ASIPP SOL Edge Poloidal dispersion relations measured at 12 radial locations

  17. Questions presented for discussion • Evidence for ballooning structures of plasma turbulence in HT-7 • Zonal flows measurements in HT-7 • Electrostatic coherent mode in HT-7 • Multi-scale coherent structure in plasma turbulence • Open questions

  18. HT-7 ASIPP Low frequency coherent mode in HT-7 10~20 kHz electrostatic coherent mode was frequently observed in the plasma edge region of the HT-7 tokamak.Our special designed new experiments clearly demonstrated that this coherent mode is strongly correlated with tearing mode activity in the plasma core region. Tearing mode 17 kHz Langmuir probe 10 kHz magnetic coils

  19. P1 Cross section Mirnov coils P2

  20. Potential fluctuation spectra measured by Langmuir probe at plasma edge MHD spectrum Measured by Mirnov coils 9 kHz 18 kHz MHD spectrum Measured by Mirnov coils

  21. HT-7 ASIPP Correlation between two potential signals toroidally separated by about 90° Turbulence is almost completely decorrelated, while MHD perturbations have strong correlation in long distance.

  22. Global magnetic field perturbations induced by rotating islands of tearing mode Coupling of the global magnetic field perturbations with the local electron drift mode  large-scale electrostatic perturbations

  23. HT-7 ASIPP Poloidal rake probe MHD spectrum Measured by Mirnov coils

  24. HT-7 ASIPP

  25. Questions presented for discussion • Evidence for ballooning structures of plasma turbulence in HT-7 • Zonal flows measurements in HT-7 • Electrostatic coherent mode in HT-7 • Multi-scale coherent structure in plasma turbulence • Open questions

  26. Different mode number overlapping

  27. Turbulence structure at plasma edge long correlation tail from 12.5 to 100 s 4 cm inside the LCFS, averaged lifetime of turbulence eddies is around 25 s. lifetime of the largest turbulence eddy is about 100 s, beyond this time scale the fluctuation is completely decorrelated.

  28. Intermittently occurring large-scale coherent structures mainly in low frequency region

  29. Typical drift-wave dispersion relation Turbulence propagates in the electron diamagnetic direction with phase velocity Vph ~ 2 km/s. Turbulence concentrates in low frequency and long wavelength region. Decay towards high frequency and short wavelength region. Two dimension FFT Dispersion relation Vph = 2 km/s

  30. Large-scale coherent structure : poloidal scale > 6 cm, time scale > 50 s Small-scale coherent structure : poloidal scale < 1 cm, time scale < 10 s Coiflet wavelets (a biorthogonal wavelet) are used to extract these structures

  31. Intermittency Structures self-similarity

  32. Use singular value decomposition method to see the multi-scale structures of plasma turbulence Sort according to signal magnitude Large-scale

  33. Large-scale structures have long lifetime up to 100 s

  34. HT-7 ASIPP Open questions • Which mode is responsible for plasma turbulence at tokamak edge? Particular instability at plasma edge or spreading from the core region? • Plasma turbulence structure in tokamaks is ballooning or not? • Besides zonal flows, local parameters (n, T, p) changing (with r) is also a possible reason for breaking the global enginemode structure and the presence of mesoscale ballooning structures. • Big eddy not necessarily implies big contribution to transport. The traditional fluid picture of convection transport need to be reconsidered. Particles scattering by wave  diffusive transport Thanks for your attention.

  35. Filamentary structures or blob structures in plasma turbulence were observed in some tokamaks recently by imaging: TFTR, ASDEX, Alcator C-Mod, DIII-D, NSTX. // >> 1 m (qR~10 m),  = 1~10 cm. beam emission spectroscopy (BES) gas-puff imaging (GPI) Alcator C-Mod Grulke, Terry, LaBombard, Zweben Phys. Plasmas 13, 012306 (2006) NSTX Maqueda, Wurden, Zweben Rev. Sci. Instrum. 72, 931 (2001) Not ELMy !

  36. Alcator C-Mod Terry, LaBombard, Zweben, http://www.pppl.gov/~szweben/index.html Side view Tangential view Top view

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