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Spontaneous stationary toroidal rotation in the TCV tokamak

Spontaneous stationary toroidal rotation in the TCV tokamak. A. Scarabosio, A. Bortolon, B. P. Duval, A. Karpushov and A. Pochelon 10 th ITPA TP Group Meeting. Layout of the talk. The DNBI and CXRS diagnostic on TCV - The effect of the DNBI on toroidal rotation.

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Spontaneous stationary toroidal rotation in the TCV tokamak

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  1. Spontaneous stationary toroidal rotation in the TCV tokamak A. Scarabosio, A. Bortolon, B. P. Duval, A.Karpushov and A. Pochelon 10th ITPA TP Group Meeting 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  2. Layout of the talk • The DNBI and CXRS diagnostic on TCV - The effect of the DNBI on toroidal rotation • Stationary toroidal rotation in limited ohmic L-mode:1 • - Plasma current scan and effect of sawteeth • - Density dependence, basic scaling and Ti-vsimilarity • - Comparison with neoclassical predictions • - Inverted rotation regime at high Ip and ne2 • Stationary toroidal rotation in H-mode • - Ohmic regime with small and frequent ELM’s • - ECH heated H-mode with large ELM 1 A. Scarabosio et al., Plasma Phys. Control. Fusion 48 (2006) 663–683 2 A. Bortolon et al., to be submitted to PRL 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  3. The TCV DNBI-CXRS system 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  4. CXRS: the TCV rotation diagnostic Doppler shift of CVI 529 nm charge exchange recombination line is measured Magnetic axis is moved vertically to change radial coverage Monochromator • Czerny-Turner (f/7.5, 5.5Å/mm) • 2400 l/mm holographic grating • CCD front illuminated detector Diagnostic Neutral Beam Injector (H0) • Extracted current 3A, acceleration voltage 50 kV • Injected power < 80 kW (20-70% absorbed) • Small injection angle: 11.25º 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  5. TCV parameters and conventions • Plasma height max. 1.44m • Plasma width max. 0.48m • Plasma major radius0.875m • Plasma current1.2MA • Plasma elongation max. 3 • Aspect ratio3.6 • Toroidal magnetic field max.1.43T 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  6. CXRS signals analysis • Standard set up: • DtNBI pulse=Dtint = 30 ms • sample rate 90 ms (It may reduced to 45 ms) Charge exchange background subtraction by means of DNBI modulation • Wavelength calibration from reference Ne spectrum (Ne lamp) after each shot. • Typical uncertainty: ±2 km/s in the core ±5 km/s in the edge 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  7. The effect of the DNBI on rotation • Experiments with 180 ms NBI pulse length • Sawtooth precursors frequency is modulated by the neutral beam! • Max. excursion of ~1 kHz  6 km/s • Simple 3 three forces one-dimensional model: • Exponential solution with characteristic time on~ off~60-80 ms • 1-2 km/s beam induced velocity for 30 ms beam pulse length 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  8. Spontaneous rotation in limited L-mode ohmic plasmas 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  9. Plasma current scan: typical exp. # 27098 Database of ohmic limited L-mode • qE = 2.4 - 8 • Ip =-350 - +320 kA • <ne> =1.4 - 71019 m-3 •  = 1.15 - 1.5 • = -0.4 - 0.4 Te = 500 -1600 eV Ti = 150 - 700 eV p = 0.2 - 1 li = 0.8 - 2 • No simultaneous high ne and low qE! • Very basic experiments in steady state condition and ohmic limited L-mode regime • Average over several profiles (~10) to minimize errors 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  10. Plasma current scan: rotation profiles • Counter-current carbon rotation also confirmed by MHD spectroscopy. • (electron diamagnetic drift) of • several tens of km/s • Central rotation increases with • qE. • Peak profile in the outer region • and flat or hollow central profile. • Knee in profiles correlates with • position of the sawtooth inversion radius from SXR. • Expected (from neoclassical theory) deuterium rotation (dashed lines) differs significantly in the low current case 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  11. Negative plasma current scan Negative current scan Comparison positive-negative Ip qE~6 # 27484 # 27098 • Same profile within the errors: • - same absolute rotation velocity in the core plasma. • - some difference in outer part profile (not due to the beam! • - radial shift of ~1cm (ex. error in equilibrium reconstruction) can explain difference in outer region (>0.4) • co-current rotation (ion diamagnetic drift) with similar velocities and profile shape with respect to Ip>0 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  12. Edge profiles with Zaxis scan • By varying (from shot to shot) the axis vertical position we get the edge rotation profile too! • Data consistent with  being a flux function • Inverted (co-current) edge rotation =+3 km/s as suggested by current scan experiments (but large error bar!!) qE=4.4 ne=2.5 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  13. Sawteeth flatten core rotation Rotation profiles response to a flattened current profile by off-axis ECH # 27677 • 500 kW of off-axis ECH power. • The temperature and current profiles flattened inv from 0.35 to 0.15. •  • Rotation profile peaks when inv is reduced 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  14. v-Ti similarity • Strong similarity (same gradient) between the rotation and temperature profile from CXRS outside inv. # 27098 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  15. Scaling law of toroidal rotation • v,Max (~v(inv)) scales linearly with the plasma current and ion temperature v,Max [km/s]= -12.5 Ti,0/Ip [eV/kA] • Averaged values on steady state discharges • For qE3.2 deviate from this scaling 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  16. Neoclassical prediction: effect of Er Er and diamagnetic contribution • Neglecting E1: • In this configuration TCV rotation dominated by EB flow 1Kim Y B et al 1991 Phys. Fluid B 3 2050–60 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  17. Neoclassical prediction • In neoclassical theory the radial angular momentum flux has a diffusive part (velocity gradient) and a non-diffusive part related with gradients in plasma parameters. 1,2 • The steady state condition in absence of external momentum input: 1Catto P J and Simakov A N 2005 Phys. Plasmas 12 012501 2Wong S K and Chan V S 2005 Phys. Plasmas 12 092513 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  18. Spontaneous rotation in limited L-mode ohmic plasmas (2) High density- high current plasma A new rotation regime 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  19. Inverted core rotation at high Ip and ne Ip ~ 340 kA, qe ~ 3.5 • t = 1.1s (ne0 = 6x1019 m-3) • carbon toroidal velocity flips • from -12 to +12 km/s • change in toroidal rotation also observed • on MHD mode rotation frequency Low ne or low Ip  counter-current rotation High ne and high Ip core co-current rotation • see next presentation of A. Bortolon for details! 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  20. Spontaneous rotation in H-mode ohmic and ECH plasmas 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  21. Toroidal rotation in ohmic H-mode • Ohmic, diverted H-mode with frequent ELM’s. (Ti(0.6)=600 eV, q95=2.5) • Standard H-mode at Zaxis=20 cm  limited radial coverage • Co-current rotation in the observed region • Only outer region available  no core rotation measurements  10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  22. Toroidal rotation in ECH H-mode • Central X3 ECH increases stored energy. Ti(0.6)~1000 eV!! • New ELM regime, less frequent but more energy released. • Co-current rotation increases with stored energy and Ti • MHD mode rotation frequency confirms co-current rotation 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  23. Conclusions • Carbon toroidal rotation, with negligible external input (spontaneous), is routinely measured in TCV L-mode and recently in H-mode discharges. • Toroidal rotation shows a rich phenomenology: • Counter-current rotation in limited L-mode at low ne or Ip • Core co-current rotation in limited L-mode at high ne and high Ip • Co-current rotation in ohmic and ECH heated H-mode (core and edge) • Similarity between v and Ti (in L-mode v [km/s]=-12.5Ti/Ip [eV/kA] • Neoclassical predictions of radial flux of angular momentum does not agree with L-mode TCV data (H-mode??) 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  24. Directions of future researches Hardware improvements • Up-grades of the DNBI • - New arc source (full energy fraction 60 → 85%) • - Reduced beam divergence (0.8 → 0.5 degrees ) • - A/P ratio increased by a -factor of 2.5-3 without increasing deposited power • Up-grades of CXRS: • - New back illuminated CCD detector (QE X4) • - New bundle of optic fibers (8 to 20 measurement points) • New vertical CXRS view to measure poloidal rotation is under commissioning Physics issues • Effect of divertor on edge and core plasma rotation • Central rotation in H-mode plasmas • Establish a scaling law for H-mode plasmas • Study toroidal rotation in plasmas with ITB’s 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  25. Extra slides 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  26. Density scan at low Ip 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  27. Empirical momentum flux k~1 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  28. MHD Spectroscopy 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  29. Sawteeth flatten core rotation invvs. s = width of the flat region in the rotation profile • Good correlation between inv and the outer position of the flat rotation region. • For large inv profile is hollow even outside inv. • Existence of a co-current torque? Negative Ip Positive Ip 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  30. MHD spectroscopy #29500 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  31. Neoclassical prediction: effect of E E contribution to C rotation • The neoclassical drive1 from E to V// is negligible for TCV ohmic plasmas 1Kim Y B et al 1991 Phys. Fluid B 3 2050–60 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  32. Overview on #29475 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  33. Temporal evolution #29475 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  34. 40 vertical chords for poloidal velocity measurement Czerny-Turner monochromator Back illuminated CCD Vertical CXRS 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

  35. Energy confinement time as a function of *e (ne,Ip)  *e • No power degradation or or Ip effect!  Rotation inversion depends on collisionality and plasma current! 320 kA 290 kA 340 kA 370 kA Collisionality at rotation inversion  Time 10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio

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