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Centre de Recherches en Physique des Plasmas EPFL, Association Euratom-Fédération Suisse, Lausanne, Switzerland S. Coda, U.S.-E.U. Joint Transport Task.

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Presentation on theme: "Centre de Recherches en Physique des Plasmas EPFL, Association Euratom-Fédération Suisse, Lausanne, Switzerland S. Coda, U.S.-E.U. Joint Transport Task."— Presentation transcript:

1 Centre de Recherches en Physique des Plasmas EPFL, Association Euratom-Fédération Suisse, Lausanne, Switzerland S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 Geodesic acoustic modes: simultaneous observation of density, magnetic-field, and flow components in the TCV tokamak S. Coda, C.A. de Meijere, Z. Huang, L. Vermare 1, T. Vernay, V. Vuille, S. Brunner, J. Dominski, P. Hennequin 1, A. Kr ä mer-Flecken 2, G. Merlo, L. Porte S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 1 LPP, CNRS-Ecole Polytechnique, Palaiseau, France 2 Forschungszentrum J ü lich, Germany

2 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 2 Geodesic acoustic modes Multi-diagnostic measurements of GAMs in TCV Modeling of GAMs in TCV Summary and outlook Outline

3 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 3 Electric potential perturbations: symmetric over flux surface (m=n=0), low-frequency (   0) Nonlinearly generated by broadband drift-wave turbulence EAssociated poloidal, sheared (k r ≠ 0) E  B flows break apart turbulent eddies and effectively regulate turbulence  self-organization Zonal flows

4 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 4 Finite-frequency (  c s /R) zonal-flow component n=0, m=1 standing-wave density fluctuation n=0, m=2 standing-wave magnetic component (recent prediction, Wahlberg 2009) Geodesic acoustic modes  recent proposal to excite GAM with external magnetic perturbation (Hallatschek 2012)

5 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 5 Flow and density components observed on several devices (Doppler backscattering, reflectometry, beam emission spectroscopy, heavy ion beam probe) Geodesic acoustic modes

6 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 6 Geodesic acoustic modes Multi-diagnostic measurements of GAMs in TCV Modeling of GAMs in TCV Summary and outlook Outline

7 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 7 Density: tangential phase contrast imaging Magnetic field: Mirnov coils Flow: Doppler backscattering Radiative temperature: correlation ECE GAMs in TCV Unique, correlated multi-diagnostic observation First sighting of magnetic-field component for turbulence-driven GAM Axisymmetry unambiguously determined

8 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 8 Initial study: L-mode, limited plasma with 1 MW central ECRH  magnetic analysis then extended to broad range of past shots (including Ohmic)

9 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 9 TCV R = 0.88 m, a = 0.25 m I p < 1 MA, B T < 1.54 T  < 2.8, -0.6 <  < 0.9 ×4 ×2 4.5 MW ECRH power, 7 steerable launchers

10 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 10 Established technique for measuring line-integrated density fluctuations Tangential geometry + spatial filtering adds spatial resolution Tangential phase contrast imaging (TPCI)

11 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 11 Ultimate specs: 0.9 cm -1 < k < 60 cm -1 (0.2 < k  s < 90) spatial resolution down to 1% of minor radius multi-MHz bandwidth Tangential phase contrast imaging (TPCI)

12 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 12 Current specs: 1 cm -1 < k < 9 cm -1 line-integrated measurement only 1.5 MHz bandwidth Tangential phase contrast imaging (TPCI)

13 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 13 k is radial  TPCI signal comes from tangency point scan  by moving plasma vertically TPCI provides GAM’s spatial distribution and radial wavelength

14 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 14 TPCI provides GAM’s spatial distribution and radial wavelength

15 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 15 22-40 kHz peaks near edge k   1.7-2.1 cm -1 (mainly outward) k  s  0.4-0.5

16 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 16 Magnetic component of the GAM

17 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 17 B  ( , ,t)  q 2  sin(2  ) sin(k   -  t) Theory: magnetic component of the GAM short radial wavelength: faint signal outside plasma nodes on LFS and HFS, so toroidal mode number should be measured away from equatorial plane

18 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 18 Magnetic component of GAM has n=0

19 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 19 At GAM node location, residual signal dominated by n=1 toroidal mode number n

20 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 20 Magnetic component of GAM has m=2

21 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 21 Magnetic component of GAM has m=2 antinodes and LFS phasing consistent with sin(2  )

22 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 22 Magnetic component of GAM has m=2 HFS phasing indicates presence of m>2 components (effect of shape?)

23 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 23 GAM scales with sound speed

24 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 24 Doppler backscattering on TCV Flow measurements performed with a 50-75 GHz tunable, heterodyne system on loan from LPP and Tore Supra  Collaboration with LPP (L. Vermare and P. Hennequin) 1 Monostatic antenna = replica of ECRH launcher, can be oriented in real time 1 L. Vermare et al, Nucl. Fusion 52, 063008 (2012)

25 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 25 Doppler backscattering on TCV

26 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 26 Oscillating E  B GAM poloidal flow is clearly seen in the edge region GAM flow  0.7 km/s rms (background flow  2 km/s)

27 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 27 GAM seen also by correlation ECE Six-channel tunable X2 system, LFS detection

28 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 28 Strong correlation between TPCI & ECE

29 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 29 GAM on C-ECE vs TPCI: a few puzzles plasma is invariably optically thin (  <0.5): ECE measurement is unknown mix of n e and T e fluctuations k  (TPCI)  1.7-2.1 cm -1, k  (C-ECE)  0.9 cm -1 predominantly outward-propagating on TPCI, propagation direction depends on location on C-ECE

30 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 30 Global vs local GAM All diagnostics on TCV see a single-frequency mode irrespective of location Other devices have reported a single-frequency mode, several discrete modes, or a continuum over  This variation in behavior is not well understood

31 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 31 Geodesic acoustic modes Multi-diagnostic measurements of GAMs in TCV Modeling of GAMs in TCV Summary and outlook Outline

32 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 32 ORB5: global particle-in-cell ∂ f code Collisionless, electrostatic simulation using TCV experimental equilibrium and kinetic profiles: turbulence is dominated by trapped electron modes Model breaks down for  > 0.85, so simulation restricted to inner region (fluctuation level artificially scaled down in edge) Gyrokinetic modeling

33 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 33 Good, semi-quantitative agreement between experiment and modeling

34 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 34 Good, semi-quantitative agreement between experiment and modeling Multiple discrete modes below a critical density gradient, single mode above (as in experiment)

35 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 35 Good, semi-quantitative agreement between experiment and modeling k   2.3 cm -1 coherent over several wavelengths f  33 kHz peak amplitude 3 km/s rms peaks at outermost properly simulated radius (  =0.85)

36 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 36 Geodesic acoustic modes Multi-diagnostic measurements of GAMs in TCV Modeling of GAMs in TCV Summary and outlook Outline

37 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 37 Initial study on TCV has revealed GAM in density, magnetic-field, and flow fields (plus ECE radiative temperature) First multi-probe analysis of magnetic component has clearly confirmed axisymmetry Frequency, radial wave number, poloidal and toroidal mode numbers, radial profile, direction of propagation have all been measured Good agreement with gyrokinetic modeling Summary

38 S. Coda, U.S.-E.U. Joint Transport Task Force Workshop, Santa Rosa, CA, 9-12 April 2013 GAMs in TCV 38 Much more to come from the experiment: parametric studies (dependence on q profile, shape, collisionality, etc.), exploration of damping mechanism, etc. Better diagnostics will be used: fully commissioned TPCI, C-ECE using movable antenna Much more to come from modeling: synthetic diagnostics for TPCI and C-ECE, parametric studies, etc. Further challenges to theory: e.g. m>2 magnetic GAM components (finite- , toroidicity effects) Outlook

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