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Interplay between neoclassical and turbulent transport on Tore Supra

Interplay between neoclassical and turbulent transport on Tore Supra.

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Interplay between neoclassical and turbulent transport on Tore Supra

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  1. Interplay between neoclassical and turbulent transport on Tore Supra Acknowledgements: J. Abiteboul, F. Clairet, C. Fenzi, S. Futatani1, V. Grandgirard, R. Guirlet, O. Gürcan2, P. Hennequin2, S. Heuraux3, H. Lütjens4, R. Sabot, Y. Sarazin, E. Trier2, L. Vermare2, D. Villegas, and the Tore Supra Team X. Garbet IRFM, CEA Cadarache 1Iter Organisation,2LPP Ecole Polytechnique, 3IJL Nancy, 4CPhT Ecole Polytechnique

  2. Motivation and outline • Usual statement : perpendicular transport is turbulent, parallel dynamics is collisional – in practice, a competition. • When axisymmetry is lost, competition between turbulence and collisional processes is exacerbated. Outline • Large scale flows : competition between turbulence Reynolds stress and viscous damping • Particle transport : competition between Ware and turbulent pinch velocities – Perp. diffusion is enhanced in presence of helical perturbations.

  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) Turbulence diagnostics and codes on Tore Supra Casati 09

  4. Large scale flows : interplay between turbulence generation and collisional damping • Tore Supra: large (7%)magnetic field ripple • Leads to magnetic braking in toroidal direction – controls radial electric field. • Competes with turbulence Reynolds stress

  5. Reynolds stress  Viscous damping Flow dynamics • Radial force balance equation • Reynolds stress + collisional viscous damping (w/o MHD , fast ion losses) Diamond 05  determine V , V , et Er

  6. Hennequin 09 Z (m) 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 R (m) Rotation measurements Doppler reflectometry • Scan in ripple : plasma size • Doppler reflectometry Assumption : Vph « -Er/B - supported by simulations direct measurement of Er • CXRS: measurements of V CXRS

  7. 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, Kovrizhnykh 99 r/a=0.6

  8. Fenzi 10 Co-rotation V Cntr ripple Intrinsic toroidal rotation • Counter-rotation in Ohmic plasmas for large ripple • Co-rotation with smaller ripple. Consistent with competition between ripple friction and turbulent Reynolds stress Hahm 07, Peeters 07, Gurcan 08, Diamond 09, …

  9. Dif-Pradalier 08 kneo [Kim '91] Collisionality Neoclassical viscous damping • Strong collisional friction at the passing/trapped boundary • Poloidal flow scales with T:

  10. 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.

  11. Reynolds stress important for shear flow • VVneo, but velocity shear is different • ExB shear not the same with or w/o turbulence Sarazin 10

  12. Is the poloidal rotation neoclassical on Tore Supra? • Doppler reflectometry  Eralways agrees with ripple=0 in the core • CXRS  Vchanges from cntr to co-rotation when ripple becomes weaker • Radial force balance equation  VVneo at low ripple • Not impossible (e.g. JET Crombé 06, DIII-D Kim 94 TFTR transient Bell 98 ) but surprising : turbulencesimulations findVVneo+ turbulence corrugations

  13. Particle and impurity transport in the plasma core (q<1) • Usual form of particle transport =-Dn+Vn • Usually D,V >> Dneo,Vneo • Not always true in the core, where values get closer to neoclassical (“neoclassical” here means axisymmetric value)

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

  15. Particle pinch is usually turbulent on Tore Supra • Long pulses (6mn) with LHCD  Eind0  Ware pinch=0 • Ionization source localised in the edge, pinch due to waves is small.  V (electrons) is turbulent Hoang 04

  16. Transport during sawtoothing ohmic plasmas Guirlet 08 • Pinch velocity close to Ware value, diffusion is not neoclassical

  17. Fluctuation level is low inside q=1Dturb is small R

  18. 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 gas injection or laser blow-off. • 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.

  19. Guirlet 10 D and V for electrons and Nickel vs neoclassical Impurities are neoclassical in the core, electrons are not • Vnickel and Dnickel are neoclassical • How is it possible to get De>>DNiDNi,neo >>De,neo • Simplest theory c,Ni<< c,e ???

  20. Is the internal kink mode responsible for high De? • m=1,n=1 activity part of the time • Estimation of magnetic field amplitude a few 10-3 Sabot 10

  21. Orders of magnitude Ellectrons: banana-drift regime Nickel: ripple-plateau regime • In summary: • Collisional electron transport is enhanced–still off by a factor 3-5 • Ni neoclassical transport is unchanged

  22. Conclusions • GK simulations show that VVneobut radial corrugations due to turbulence are not negligible. • Er and Vagree with neoclassical theory in ohmic plasmas, with strong ripple. Situation at low ripple is unclear: looks like V departs from Vneo. • Some evidence that in the core, collisional transport due to n=1,m=1 helical perturbation can matter

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