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Measurements and modelling of turbulent transport on Tore Supra

Measurements and modelling of turbulent transport on Tore Supra.

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Measurements and modelling of turbulent transport on Tore Supra

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  1. Measurements and modelling of turbulent transport on Tore Supra Acknowledgements: J. Abiteboul, P. Angelino1, S. Benkadda2, C. Bourdelle, A. Casati1, F. Clairet, G. Falchetto, C. Fenzi, S. Futatani2, T. Gerbaud3, V. Grandgirard, R. Guirlet, O. Gürcan4, P. Hennequin4, S. Heuraux5, G.T. Hoang, C. Honoré4, R. Sabot, Y. Sarazin, A. Sirinelli3, E. Trier4, L. Vermare4, D. Villegas. X. Garbet IRFM, CEA Cadarache 1 EPFLLausanne 2PIIM Marseille 3 UKAEA Culham 4LPP Ecole Polytechnique, 5IJL Nancy

  2. Outline • Comparison between fluctuation measurements and simulations – towards a reduced transport model. • Large scale flows : competition between turbulence generation and collisional damping • Impurities astracers of turbulent transport

  3. 2 Doppler and 2 fast sweeping reflectometers: profile of turbulence intensity, frequency and wavenumber spectra Numerical tools: global (GYSELA) local (GYRO, GENE) gyrokinetic codes, integrated modelling (CRONOS) k i k s k Cut-off layer Diagnostics and codes on Tore Supra

  4. poloidal r  Radial  toroidal Geometry

  5. Is it possible to build a reliable reduced transport model? • Most models are based onquasi-linear theory Vedenov 61, Drummond 63 and a mixing-length rule Prandtl 25, e.g. • Some open questions : validity of QL theory, better description of fluctuation spectra.

  6. Dannert 05 Casati 08 - GYRO Cross phasevE-T Wave number ki Phase Test of Quasi-Linear Theory • QLT assumes linear cross-phase • Looks like a reasonable hypothesis at low k. Seems to work even close to threshold. • Factor 1.4 between simulations and QLT Waltz 08

  7. Agreement is found between density fluctuation measurements and simulations. Casati 09

  8. Gurcan 09 Wave number spectra are also well reproduced Slope always the same NL effects dominant. Discrepancies between simulations : inward propagating GAMs in GYSELA. Zonca 08 Change of slope is usually observed at ki1Hennequin 04.Possible effect of zonal flows Gurcan 09. Casati 09

  9. GYRO simulations of k spectra Fast sweeping reflectometry provides information on kr spectra Casati 09 • Access to distribution of density perturbations kr spectra Vermare 04 • Spectrum index is different : instrumental effect • Spectra are isotropic at high k

  10. Casati 09 Frequency spectra • Measured with Doppler reflectometry Hennequin 06 • k  k- kk, agrees with convective /diffusive model Hennequin 99 • Ongoing modelling with EDQNM Krommes 92 Hennequin 09

  11. Predicted temperature Present status of transport modelling • Qualikiz : QLT, k-3 spectrum (+ cut-off Dannert 05), lorentzian frequency spectrum. Bourdelle 08 • Encouraging results, except at low magnetic shear. Casati 09 – GYRO (pts) vs Qualikiz

  12. Large scale flows : interplay between turbulence generation and collisional damping • On Tore Supra, magnetic field corrugation (ripple) is large (7%) • Leads to magnetic braking in toroidal direction • Competes with turbulence Reynolds stress

  13. Reynolds stress  Viscous damping Flow dynamics • Force balance equation • Reynolds stress + collisional viscous damping Smolyakov 09  determine V , V , et Er

  14. Z (m) 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 R (m) Rotation measurements Doppler reflectometry • Doppler reflectometry Assumption : Vph « -Er/B - supported by simulations direct measurement of Er • CXRS: measurements of V CXRS

  15. Radial electric field Trier 08 • Radial electric field is negative : controlled by thermal ripple losses • Local trapping krip=3.37Connor 73 . Ripple-plateau krip=1.5Boozer 80 r/a=0.6

  16. Intrinsic toroidal rotation Fenzi 09 Ti • Counter-rotation in Ohmic plasmas. Co-rotation with smaller ripple. • Consistent with competition between ripple friction and turbulent Reynolds stress. V Co-rotation Ripple  Cntr r/a

  17. Dif-Pradalier 09 vqTotal vqNeo Poloidal rotation agrees with neoclassical theory in global simulations • Consistent with poloidal viscous damping • However: large corrugations due to turbulent Reynolds stress.

  18. Disagreement on poloidal rotation? • Doppler reflectometry  Er agrees with ripple=0 in the core • CXRS  Vchanges from cntr to co-rotation when ripple becomes weaker • VVneo? e.g. JET Crombé 06, DIII-D Kim 94 • Turbulencesimulations findVVneo+ turbulence corrugations

  19. Particle and impurity transport • Ion heat transport well known, particle and electron heat transport make progress, impurity transport not well documented • Related to turbulent transport of passive tracers for low impurity concentrations • Reference is collisional transport in axisymmetric systems: neoclassical theory

  20. Particle pinch is turbulent Diffusion and pinch velocity vs radius - TORE SUPRA -G.T. Hoang 04 • Particle flux of the form =-Dn+Vn • Unambiguous observation of an anomalous pinch in TS long pulses Hoang 04, (Ware pinch=0)

  21. Guirlet 08 Dtrans+stat 1.5 1 0.5 0 0.6 0.6 0.4 0.4 0.2 0.2 0 0 Vtrans+stat 2 0 -2 -4 -6 r/a What about impurities? • Supersonic impurity gas injection. • Both transient and steady profiles are used to assess fluxes =-Dn+Vn • Allows to reduce error bars on D and V by a large factor.

  22. Modelling of transient confirm the diffusion/convection model Futatani 10

  23. sawtoothing plasma, between sawteeth sawtooth free plasma 10 10 DexpNi DexpNi DturbNi 1 1 m2/s m2/s DturbNi 10-1 10-1 10-2 10-2 DneoclassNi DneoclassNi 0.6 0.4 0.2 0 0.6 0.4 0.2 0 r/a r/a Impurity transport is turbulent • Diffusion is always turbulent in the gradient zone • Qualitatively agree with quasilinear theory (Qualikiz). Guirlet 08

  24. Evidence of a critical gradient Villegas 10 • Evidence of an instability threshold • Agrees with expectation from drift wave (ITG/TEM) model DNi vs temperature log. gradient

  25. Total convection velocity VNCLASS 0 Vturb m/s -2 Vexp -4 0.6 0.4 0.2 0 r/a Impurity transport depends weakly on charge number • D and V depend weakly on the charge number (7<Z<32) – also agrees with QualiKiz. Different from JET? • Pinch velocity directed inward. Bourdelle/Guirlet 08

  26. Guirlet 10 D and V for electrons and Nickel vs neoclassical Impurities are neoclassical in the core, electrons are not Sabot 10 • Low level of fluctuations in the core • electron pinch velocity is above neoclassical, Vnickel is neoclassical • Effect of an internal kink mode? Level of fluctuations

  27. Conclusions • Agreement between measured and calculated density fluctuations, for both intensity and spectra quasilinear transport model under test. • Er and Vagree with neoclassical theory in ohmic plasmas, with strong ripple. Situation for V to be clarified. • Impurity transport is turbulent in the gradient zone, neoclassical in the core of Ohmic plasmas. Dependence on charge and mass numbers unclear.

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