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Nicolas Fedorczak PhD defence 24/09/2010 1 /26 Experimental investigation of Nicolas Fedorczak Thesis supervisor : A. Pocheau (IRPHE) turbulent transport.

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Presentation on theme: "Nicolas Fedorczak PhD defence 24/09/2010 1 /26 Experimental investigation of Nicolas Fedorczak Thesis supervisor : A. Pocheau (IRPHE) turbulent transport."— Presentation transcript:

1 Nicolas Fedorczak PhD defence 24/09/2010 1 /26 Experimental investigation of Nicolas Fedorczak Thesis supervisor : A. Pocheau (IRPHE) turbulent transport at the edge of tokamak plasmas CEA supervisor : P. Monier-Garbet J.P. Gunn J.P. Gunn Ph. Ghendrih Ph. Ghendrih

2 Nicolas Fedorczak PhD defence 24/09/2010 2 /26 Magnetic confinement & transport Magnetic confinement of ~10keV plasma Tokamak : // direction : free motion direction : constrained by B !! gradients (no thermo-dynamical equilibrium) + curvature transport - energy losses to the walls - pressure gradient in core plasma critical issue for reactor operation critical issue for reactor efficiency

3 Nicolas Fedorczak PhD defence 24/09/2010 3 /26 Edge transport : turbulence & asymmetry Current tokamaks : JET, DIII-D, ASDEX, Tore Supra, NSTX, TCV, Alcator C-mod … demonstrated the high level of turbulence ExB convection Picture from fast imaging on Tore Supra : Experimental evidences : interchange P + B free energy source drive instability HFS : stable / LFS : unstable demonstrated transport asymmetries Tore Supra, C-mod J.P. Gunn JNM2006 B. LaBombard NF2004 Garcia & Pitts NF2007

4 Nicolas Fedorczak PhD defence 24/09/2010 4 /26 Edge plasma influenced by plasma/wall interaction Boundary of confined plasma : open field lines region = Scrape-Off Layer delimited by the Last Closed Flux Surface Plasma facing components (PFC) : - perfect sink of particle - regulate charges & currents - spatial symmetry breaking determine the SOL plasma equilibrium (balance between // and fluxes) Heat load footprint, matter migration (flows) + boundary conditions for core rotation flows

5 Nicolas Fedorczak PhD defence 24/09/2010 5 /26 Open issues related to ITER project ITER : next step toward fusion reactor - High performances discharges - steady-state + fusion reactions Critical issues related to edge plasma No robust model to predict: - Heat load on first wall Physics of blobs, ELMs & transport barriers - Pedestal gradient (shear flow & boundary conditions) shear-flowflow boundary

6 Nicolas Fedorczak PhD defence 24/09/2010 6 /26 Build a consistent picture of particle transport at the edge Axis of my research on Tore Supra Tokamak Difficult to address from current experiments : C-mod, DIII-D, ASDEX, JET Multi-diagnostic investigation of edge turbulent transport Mach probe // flows and density profiles Rake probes electrostatic fluctuations Fast imaging & reflectometers fluctuation dynamics & asymmetries Constrain models :

7 Nicolas Fedorczak PhD defence 24/09/2010 7 /26 I. How do we diagnose the plasma phenomena 1. Langmuir probes 2. Fast visible imaging II. The model drawn from experiments on Tore Supra 1. Consistency local / global measurements III. Implications & conclusion Experimental investigation of turbulent transport at the edge of tokamak plasmas 2. 3D properties of edge particle transport : revisiting filaments

8 Nicolas Fedorczak PhD defence 24/09/2010 8 /26 Reciprocating Langmuir probes 2 hydraulic systems installed at the plasma top full radial profile collection Illustration of data collection along the probe path 200 ms !! experience strong heat flux ~MW.m -2 I

9 Nicolas Fedorczak PhD defence 24/09/2010 9 /26 Improving Mach measurements plasma collection by a biased electrode local plasma parameters : n e, T e, plasma Mach configuration : // flow velocity !! time averaged data !! I Tunnel collectorsmall cylindrical collector ? large effect on flow velocity measurements Yet, tunnel probes used only on Tore Supra… Gunn, Dejarnac (poloidal rake probe) calibration with effective collection area sensitive to collector geometry Mach collectors of the rake probe

10 Nicolas Fedorczak PhD defence 24/09/2010 10 /26 Implementing rake probes for fluctuations 1 MHz acquisition rate + ~mm spatial sampling potential & density ExB convection potential & density In charge of the final design, maintenance & use of a new diagnostic DTURB & the rake probes mode selection anti-aliasing dynamical sampling : SNR Collaboration with Gent University (G. Van Oost) Requirements for SOL plasma fluctuations: Improved control & electronics for a flexible & sensitive acquisition I

11 Nicolas Fedorczak PhD defence 24/09/2010 11 /26 Issue on the interpretation of fluctuations Turbulent flux : Discrete measurement : Effect of electric field under-sampling ? (Never mentioned in the literature) I Tokam 2D Error calculated on turbulence simulation non negligible error depends on potential eddy size Some experimental data are not exploitable for r turb !! experiment

12 Nicolas Fedorczak PhD defence 24/09/2010 12 /26 Fast imaging of edge transport phenomena Use visible plasma emission to picture the density fluctuations Rich qualitative understanding: geometrical + dynamical Tore Supra top view Camera viewVirtual view Collaboration with Nancy university + IRPHE & local plasma electrons excite neutrals & wide opening angle up to 50 kHz (effective exp turb ) I

13 Nicolas Fedorczak PhD defence 24/09/2010 13 /26 Qualitative information Movies resolve the main turbulence dynamics extraction ? reconstruction? Tangential projection of ~2D turbulence Tomographic reconstruction Collaboration LPMIA F. Brochard / G.Bonhomme + LMD R. Nguyen / M. Farge I LFS gas injection recorded @ 50kHz Velocity extraction @ midplane (reduced projection artifact) Qualitative agreement with reflectometers Collaboration LPP L. Vermare camera

14 Nicolas Fedorczak PhD defence 24/09/2010 14 /26 Transport model: diagnostics capabilities Tunnel Mach probe // flows global particle balance + spatial asymmetries Fast visible imaging spatial properties transport mechanisms + spatial asymmetries 3D transport description from experimental evidences Poloïdal rake probe local ExB turbulence transport mechanisms + local amplitude II

15 Nicolas Fedorczak PhD defence 24/09/2010 15 /26 & fluctuate in phase & fluctuate in phase Electrostatic fluctuations : interchange-like Radial convection of density bursts bursty transport Devynck, Boedo, Zweben II

16 Nicolas Fedorczak PhD defence 24/09/2010 16 /26 Electrostatic fluctuations : associated transport Intermittent convection of density bursts : qualitative agreement with fast imaging ordering consistent with density profiles but not quantitatively V r blobs > 300 m.s -1 ( 1% c S ) Averaged effect : V r plasma ~ 30 m.s -1 ( 0.1% c S ) Consistency local vs. global measurements asymmetries ? signature of filament convection? II

17 Nicolas Fedorczak PhD defence 24/09/2010 17 /26 // flow drivers in TS SOL : radial particle flux What mechanisms for // velocity // velocity density profile density profile ? PS flows probe data limiter recycling MC simulation ~15% EIRENE Y. Marandet ~10% Particle flux balance : // flow radial flux ? main driver M // n e II

18 Nicolas Fedorczak PhD defence 24/09/2010 18 /26 // flow velocity & radial flux asymmetry Particle flux balance Conservation law (pressure) // flows balance the particle source asymmetry Boundary conditions @ limiters (Bohm) quantify the global particle balance ( r into the SOL) SOL plasma partial resolution of asymmetries II

19 Nicolas Fedorczak PhD defence 24/09/2010 19 /26 r ( ) highly enhanced @ LFS ? consistency with local ExB flux ? spatial mapping flows balance: quantify LFS / HFS asymmetry conservation laws applied to local // flow profiles near sonic @ top !! II

20 Nicolas Fedorczak PhD defence 24/09/2010 20 /26 r centered @ outboard midplane in a narrow poloidal section ( 50°) Field line tailoring : resolve spatial asymmetry Use movable limiters to tailor the flux distribution along field lines quantify // flows response in term of radial flux distribution II

21 Nicolas Fedorczak PhD defence 24/09/2010 21 /26 Local / global consistency - Mach probe spatial flux distribution (global) - Rake probe ExB flux amplitude (local) Illustration for 3 different plasma scenarios : Fairly good agreement between both independent measurements ExB flux highly asymmetric (?) global local global local global local II

22 Nicolas Fedorczak PhD defence 24/09/2010 22 /26 Fast imaging: evidence of asymmetry Gas injection performed on HFS and LFS increase the visible emission pictured at 50kHz Plasma filaments are observed on LFS to propagate outward They are not observed on the HFS conciliate previous assumptions II

23 Nicolas Fedorczak PhD defence 24/09/2010 23 /26 Interpretation of multi-diagnostic investigation Particle transport in SOL : - ExB convection of plasma filaments usual flute mode paradigm - consistent with interchange instability mechanisms (localization + extent) - highly asymmetric around the plasma : - centered @ outboard midplane - finite // extent - drive near-sonic // flows around the confined plasma Necessity to consider a 3D model of filament dynamics II

24 Nicolas Fedorczak PhD defence 24/09/2010 24 /26 Picture of filaments in the core ! Other experiment : stationary fully detached plasmas (3-4 sec.) Other experiment : stationary fully detached plasmas (3-4 sec.) + local conditions ( *, P ) similar to SOL --> emissive ring in the confined region (r/a ~0.5 ) Again, (largest) field aligned structures only on the Low Field Side filaments k // > 0 + open / closed field lines II

25 Nicolas Fedorczak PhD defence 24/09/2010 25 /26 Implications of the results Database of strong evidences about edge plasma phenomena (flows, decay length, fluctuations) Case base for new code benchmarking (MISTRAL project) Coupling of turbulence & edge flows with core rotation shear layers Revisiting the theoretical description & models of edge transport flute modes = 2D full 3D (ESPOIR project) 3D description obtained on Tore Supra applicable to divertor machines coherent with other evidences conciliate apparent incoherencies L-mode : LIMITER DIVERTOR

26 Nicolas Fedorczak PhD defence 24/09/2010 26 /26 Summary Experimental investigation of edge transport : About diagnostics : - interpretation of experimental data improving probe geometry for // flow measurements - multi-diagnostic consistency critical issues on the spatial sampling of fluctuations projection artifacts with visible imaging local & global measurements About transport model : - mechanisms driving the // flows radial flux - conservation laws help from simulation (SOLEDGE2D) About experiments : + a posteriori checking - Experimental proposals dedicated to specific issues - Check the consistency of results with a variety of experiments

27 Nicolas Fedorczak PhD defence 24/09/2010 27 /26 Ionization source in the SOL Monte-Carlo simulation of recycling on main limiter : EIRENE simulation 3D domain ( toroidal symmetry) Initial input (experiment) : ion fluxes @ limiter plates (from Mach probe) n e + T e + T i profiles (SOL + confined region) Complete database for Deuterium atomic reactions Self-consistent matter balance

28 Nicolas Fedorczak PhD defence 24/09/2010 28 /26 Flux balance : Transversal drifts in SOL flux balance Simplified flux balance : |M // | ~ 1 - large aspect ratio -E r independent of

29 Nicolas Fedorczak PhD defence 24/09/2010 29 /26 Pressure conservation radial transfer of // momentum Spatial mapping of r spatial mapping of & Computable Reynolds stress P/P < 15 % ! But only linear term ! Validation with simulation SOLEDGE2D G. Ciraoloa & H. Bufferand (only viscosity) P/P < 10 %

30 Nicolas Fedorczak PhD defence 24/09/2010 30 /26 Flow reversal experiment

31 Nicolas Fedorczak PhD defence 24/09/2010 31 /26 3D filaments : revisiting momentum transfer Issue in understanding SOL flow effect on core rotation transfer of v // // dynamic of a single filament // front expansion ? coupling with local ExB fluctuations along the field line ? computable from previous results average on flux surface : NO RESIDUAL TRANSFER

32 Nicolas Fedorczak PhD defence 24/09/2010 32 /26 SOL flow and core rotation co-I P ct-I P flow reversal in SOL plasma for similar core plasma change in core velocity fields V V

33 Nicolas Fedorczak PhD defence 24/09/2010 33 /26 More experimental implications for Tore Supra 1. Heat load asymmetry on the main limiter Y. Corre & al. 2.Plasma environment of wave launchers (LH) M. Preynas, A. Ekedahl coupling efficiency (gradients in front of antennae) suprathermal electron generation V. Fuchs, J. Gunn, A. Ekedahl 3. More physics about fuelling by gas injection or pellets 4. Precise flow pattern in SOL plasma Carbon migration & deposition

34 Nicolas Fedorczak PhD defence 24/09/2010 34 /26 List of contributions First author publications : N. Fedorczak, J.P. gunn, Ph. Ghendrih, P. Monier-Garbert, A. Pocheau Flow generation and intermittent transport in the scrape-off layer of the tore Supra tokamak Journal of Nuclear Materials 390–391 (2009) 368–371 N. Fedorczak, J.P. gunn, Ph. Ghendrih, G. Ciraoloa, H. Bufferand, L. Isoardi, P. Tamain, P. Monier-Garbet, Experimental investigation on the poloidal extent of the turbulent radial flux in tokamak scrape-off layer Journal of Nuclear Materials (2010) Oral contribution to international conferences : Ballooned like transport in the SOL of Tore Supra tokamak : evidences and properties Transport Task Force meeting (TTF2009) San Diego Poloidal mapping of turbulent transport in SOL plasmas Plasma Surface Interaction meeting (PSI2010) San Diego A first comparison between probes, fast imaging, and Doppler backscattering synchronous measurements of edge turbulence in Tore Supra European Plasma Society (EPS2009) Sofia (F. Brochard & N. Fedorczak)

35 Nicolas Fedorczak PhD defence 24/09/2010 35 /26 Many thanks to Tore Supra pilots Physicists Technical support : F. Saint-Laurent, P. Hertout, D. douai, Ph. Moreau Jamie Gunn, P. Hennequin, L. Vermare, P. Monier-Garbet, P. Devynck, F. Clairet C. Reux, D. Villegas, M. Kocan, X. Garbet, Ph. Ghendrih, Y. Sarazin, P. Tamain J.Y. Pascal, B. Vincent, F. Leroux, T. Alarcon, N. Seguin, V. Negrier friends Matthieu, Sara, Sebastien, Vincent, Yannick, Matthieu, Clement, Sophie, Daniel, Gaëlle, Etienne, Cédric, Victor, Gwen, Ronan, Rémi, Matthieu, Mélanie, François, Joao, Tom, Magwa, Sparrow, Mélissa, Mai, Caro, Clemence, Dimitri, Vanessa, Julien, Lana, Alexis, Uron, Suk-ho, Timo G. Ciraolo, L. Isoardi H. Buferand, E. Serre, G. Bonhomme, F. Brochard, M. Farge, R. Nguyen, A. Pocheau, G. Searby collaborators and my family


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