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Recent Experiments on the STOR-M Tokamak

Recent Experiments on the STOR-M Tokamak. Chijin Xiao （肖持进） Plasma Laboratory University of Saskatchewan ASIPP, May 26, 2011. Outline. STOR-M tokamak program Retarding Field Energy Analyzer for Ion Temperature Measurements Helical Field Coils for MHD suppression

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Recent Experiments on the STOR-M Tokamak

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  1. Recent Experiments on the STOR-M Tokamak Chijin Xiao （肖持进） Plasma Laboratory University of Saskatchewan ASIPP, May 26, 2011

  2. Outline • STOR-M tokamak program • Retarding Field Energy Analyzer for Ion Temperature Measurements • Helical Field Coils for MHD suppression • SXR measurements for determination of MHD locations

  3. STOR-M Tokamak R = 46 cm, a (limiter) = 13 cm, Bt ~ 1 T, Ip ~ 50 kA ne ~ (1-3)x1013/cm3, Te = 200 eV PPL, Univ. of Sask.

  4. STOR-M Programs • Compact Torus (CT) injection fuelling, pressure profile (bootstrap current) control in burning plasmas • Turbulent heating, heat pulse • AC operation quasi steady state tokamak operation most efficient ohmic heating method • Diagnostics development • Plasma flow velocity measurements • Ion temperature measurement (one of the today’s topics) PPL, Univ. of Sask.

  5. STOR-M Programs (cont.) • Ohmic H-modes CT injection, plasma biasing, edge heating • MHD studies • Helical field coils  suppression of m=2 mode (one of the today’s topics) • Magnetic island structures (one of the today’s topics) PPL, Univ. of Sask.

  6. Ti Measure • Motivation for Ti measurements • RFA principles • Simulation • Model • Results • Probe design • Experimental Results

  7. Motivation for Ti Measurements • Electron temperature measurements in SOL and edge region are routinely carried out using conventional electric probes • Ion temperature measurements are scarecy and not easy • Retarding Field Analyzers (RFA) have been used in large (JET, Tore Supra) and small (ISTTOK, STOR-M) tokamaks • Precise interpretation of the data still depends on models • Technical development is still needed

  8. Importance of Ti Measurements in the Edge Region and SOL • H-mode (ETB) • Radial force balance equation Poloidal velocity shear calculation needs ion temperature and the parallel flow velocity

  9. Importance of Ti Measurements in the Edge Region and SOL • Flow measurements • Geodesic Acoustic Mode (GAM) frequency • Needs ion temperature

  10. What Can RFA Measure? • Measures ion temperature • Measures parallel flow Mach number and velocity • It is relatively simple and cost effective

  11. Principle of the RFA Pitts R.A. et al 2003 Rev. Sci. Instrum.74 11

  12. I-V curve for the RFA eVshift (>0)=min. ion kinetic energy Pitts R A et al 2003 Rev. Sci. Instrum.74 11

  13. Example I-V curve from JET Different characteristic curve different ion temperature Why? What is the true temperature? Ion side probe Electron side probe Pitts R A et al 2003 Rev. Sci. Instrum.74 11

  14. Geometry Vװ ES G1 C Bt Vװ

  15. Simulation – Derivation • Condition 2b: • Condition 3:

  16. Simulation – With Plasma Flow • Probe 1 - upstream • Probe 2 - downstream • measured

  17. Plot of measured temperature vs actual temperature with Mach number of 0.4

  18. Plot of measured temperature vs actual temperature for several probe dimensions

  19. Veco Grids • Nickel base • 283 micron by 283 micron openings • 50 micron wide bars • About 30 micron thick

  20. Probe design

  21. Probe design Dreval M., Rohraff D., Xiao C., Hirose A., 2009 Rev. Sci. Instrum.80 10

  22. Resonance helical coil experiments • Identifications of MHD modes • m/n=2/1 helical coils to supress the dominant mode • Simple model to identify required RHC current. • Experimental results

  23. SVD for mode analysis • 12 poloidally distributed coils (up to m=6 mode) • 4 toroidally distributed coils (up to n=2 mode) • Singular value decomposition spatial structure and temporal frequency of the dominant mode

  24. Resonant Helical Coils

  25. Mirnov coils

  26. SXR arrays

  27. Simple Simulations

  28. Results

  29. Expanded traces

  30. Mirnov and SXR signal amplitudes and their wavelet spectra

  31. Spatial structure of modes

  32. Spatitial Fourier analysis and the rms amplitudes of m=1 to m=4

  33. Relative mode amplitudes Before Suppression During suppression After suppression

  34. Determination of radial location of the m=2 mode • New SXR analysis techniques based on difference signals • Effectively rejects common mode noises • Reliable method for dominant single mode • May be used for mode coupling cases

  35. Active MHD activities with dominant m=2 mode

  36. SXR chords and assumed magnetic islands

  37. Assumed emissivity profile Along vertical axis

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