experimental investigation of

Nicolas Fedorczak PhD defence 24/09/2010Nicolas Fedorczak PhD defence 24/09/2010 1 /26

Experimental investigation of Experimental investigation of

Nicolas FedorczakNicolas Fedorczak

Thesis supervisor : A. Pocheau (IRPHE)Thesis supervisor : A. Pocheau (IRPHE)

turbulent transportturbulent transport

at the edge of tokamak plasmasat the edge of tokamak plasmas

CEA supervisor : P. Monier-GarbetCEA supervisor : P. Monier-Garbet J.P. Gunn J.P. Gunn

Ph. GhendrihPh. Ghendrih


Magnetic confinement & transportMagnetic confinement & transportMagnetic confinement of ~10keV plasma

Tokamak :

Z

BTBP

r

flux surfacesfield-lines

// direction : free motion direction : constrained by B

!! gradients (no thermo-dynamical equilibrium) + curvature transport

nT

r

transport

wall

- energy losses to the walls

- pressure gradient in core plasma

critical issue for reactor operation

critical issue for reactor efficiency


Edge transport : turbulence & asymmetryEdge transport : turbulence & asymmetryCurrent tokamaks :JET, DIII-D, ASDEX, Tore Supra, NSTX, TCV, Alcator C-mod …

• demonstrated the high level of turbulence

ExB convection2B

BEv

Picture from fast imaging on Tore Supra :

E = -

Tore Supra

LFSHFS

E = -

Tore Supra

LFSHFS

Experimental evidences : interchange

P + B

free energy source drive instability

HFS : stable / LFS : unstable

• demonstrated transport asymmetriesTore Supra, C-mod

J.P. Gunn JNM2006B. LaBombard NF2004

Garcia & Pitts NF2007

BB

PP

BB

PP


Edge plasma influenced by plasma/wall interactionEdge plasma influenced by plasma/wall interaction

Boundary of confined plasma : open field lines region = Scrape-Off Layer

Core plasma

SOL

closed field lines

open field lines

LCFS

particle / energy flux

plasma facing component

delimited by the Last Closed Flux Surface

Plasma facing components (PFC) :

- perfect sink of particle

- regulate charges & currents

- spatial symmetry breaking

rLCFS SOL

q//

determine the SOL plasma equilibrium

(balance between // and fluxes)

Heat load footprint, matter migration (flows)+ boundary conditions for core rotation

flows


Open issues related to ITER projectOpen issues related to ITER project

ITER : next step toward fusion reactor

- High performances discharges

- steady-state + fusion reactions

Critical issues related to edge plasma Critical issues related to edge plasma

No robust model to predict:No robust model to predict:

- Heat load on first wall

Physics of blobs, ELM’s & transport barriers

nTcore pedestal SOL

rLCFS

- Pedestal gradient

(shear flow & boundary conditions)

shear-flow flow boundary


Build a consistent picture of particle transport at the edge Build a consistent picture of particle transport at the edge

Axis of my research on Tore Supra Tokamak

radial extent radial extent Electrostatic turbulenceElectrostatic turbulence

Parallel flowsParallel flows

?

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 :


I. How do we diagnose the plasma phenomena I. How do we diagnose the plasma phenomena

1. Langmuir probes

2. Fast visible imaging

II. The model drawn from experiments on Tore Supra II. The model drawn from experiments on Tore Supra

1. Consistency local / global measurements

III. Implications & conclusion

Experimental investigation of turbulent Experimental investigation of turbulent transport at the edge of tokamak transport at the edge of tokamak

plasmas plasmas

2. 3D properties of edge particle transport : revisiting filaments


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

probe path

Confined region

I


Improving Mach measurements• plasma collection by a biased electrode

local plasma parameters : ne, Te, plasma

Mach configuration : // flow velocity

undisturbed plasma

B

V//!! time averaged data !!

I

3-5 mm

Tunnel collector

plate collectorBoron nitride

B

small collector

effective collection

area

B

Tunnel collector small cylindrical collector

? large effect on flow velocity measurementsYet, 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


Implementing rake probes for fluctuations

ISAT amplifiers16 channels

Pre filter(250kHz)

14 bits ADC2X16 channels

probes

vessel

CPU controllers

TS control room

DTURB diagnosticDTURB diagnostic

~30 m

Mode selectionVfl amplifiers

16 channels

DC power supplies

1 MHz acquisition rate + ~mm spatial 1 MHz acquisition rate + ~mm spatial samplingsampling

ExB convection potential potential && density density

In charge of the final design, maintenance & use of a new diagnostic

DTURB & the rake probes

mode selectionmode selection

anti-aliasing anti-aliasing dynamical sampling : SNR dynamical sampling : SNR

Collaboration with Gent University (G. Van Oost)Collaboration with Gent University (G. Van Oost)

Requirements for SOL plasma fluctuations:

Improved control & electronics for a flexible & sensitive acquisition

I


Issue on the interpretation of fluctuations

Turbulent flux : EnB

vn rturbr

~~1~~

en~plV

~plV~

rake probe

plpl VV

E 21

~~~

Discrete measurement :

Effect of electric field under-sampling ? (Never mentioned in the literature)

I

Tokam 2D

V

V

ne

r

Error calculated on turbulence simulation

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5

synthetic

non negligible errordepends on potential eddy size

Some experimental data are not exploitable for rturb !!

experiment


Fast imaging of edge transport phenomena Use visible plasma emission to picture the density fluctuations

Rich qualitative understanding: geometrical + dynamical

ICRH pellet

pellet SMBI

SMBI

SMBI

Tore Supra top view

Camera view Virtual view

Collaboration with Nancy university + IRPHE

turbatomicrelax turb

ionisationmfp &local plasma electrons local plasma electrons

excite neutralsexcite neutrals &

wide opening angle

up to 50 kHz (effective exp turb )

I

SMBISMBI SMBISMBI

High field side

Low field side


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

cmturberr 1~~

ILFS gas injection recorded @ 50kHz

V ~ 850 m.s-1

V ~ -400 m.s-1

Vr ~ 500 m.s-1

Equatorial midplane

LCFS Velocity extraction @ midplane

(reduced projection artifact)Qualitative

agreement with reflectometers

Collaboration LPP L. Vermare

camera


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 //

probes

rturb

fast imaging

II


Vfl

Vfl

ne

E

EnB

vn rturbr

~~1~~

n~ E~

& fluctuate in phase & fluctuate in phase

probeprobe

SOLSOL

LCFSLCFS

BBT T IIPP

Electrostatic fluctuations : interchange-like

Radial convection of density burstsRadial convection of density bursts

“bursty” transportDevynck, Boedo, Zweben

II


Electrostatic fluctuations : associated transport Intermittent convection of density bursts :

qualitative agreement with fast imaging

ordering consistent with density profiles but not quantitatively

1-ms30

rV

1-ms 300

rV

Vrblobs > 300 m.s-1 ( 1% cS )

Averaged effect : Vrplasma ~ 30 m.s-1 ( 0.1% cS )

V ~ 850 m.s-1

V ~ -400 m.s-1

Vr ~ 500 m.s-1

Equatorial midplane

LCFS

Consistency local vs. global measurements asymmetries ?

signature of filament convection?

II

rr vnn

V ~~1


// flow drivers in TS SOL : radial particle flux

cm 5.4

exp

r

re

arn

What mechanisms forWhat mechanisms for

• // velocity// velocity

• density profiledensity profile

??

ionr

rr SB

Envn )( ////

“ PS flows”probe data

limiter recycling MC simulation

~15%

EIRENE Y. Marandet

~10%

Particle flux balance :

// flow radial flux?

main driver M//

ne

II


// flow velocity & radial flux asymmetry

)( //// rrvn Particle flux balance

LIM

ITE

R

LIM

ITE

R

LCFS LCFSrr

// flows// flowsMagnetic field lineMagnetic field line

confined plasmaconfined plasma

Conservation law (pressure) 0 22//// Scnvn

// flows balance the particle source asymmetry

Boundary conditions @ limiters 12// M (Bohm)

quantify the global particle balance (r into the SOL)

SOL plasma

partial resolution of asymmetries

II


LFSLFS

probeprobe

HFSHFS rLFSr

HFS

• r() highly enhanced @ LFS

? consistency with local ExB flux ?

spatial mapping

flows balance: quantify LFS / HFS asymmetryconservation laws applied to local // flow conservation laws applied to local // flow profiles profiles

cm 5.4

exp

r

re

arn

M// profile @ top

0 0.02 0.04 0.06 0.08 0.1

0.2

0.40.4

0.6

0.8

1

r – a (m)

M//

near sonic @ top !!

<r>LFS

<r>HFS

> 20

II


r centered @ outboard midplane in a narrow poloidal section (50°)

reference

r

private

r

S

dl

dlf

// //

// //

Field line tailoring : resolve spatial asymmetryUse movable limiters to tailor the flux distribution along field lines

quantify // flows response in term of radial flux distribution

IIL

IMIT

ER

LIM

ITE

R

LFSHFS

probe r

LIM

ITE

R

LIM

ITE

R

LFSHFS

probe

2nd limiter

private region

r// //

LIM

ITE

R

LIM

ITE

R

LFSHFS

probe r

LIM

ITE

R

LIM

ITE

R

LFSHFS

probe

2nd limiter

private region

r// //

r

l//


TS44789r – a = 2.5 cmlad = 2.6 1019 m-2

TS44789r – a = 2.5 cmlad = 4.5 1019 m-2

TS44635r – a = 1 cmlad = 5 1019 m-2

43° 47° 52°r ExB

r ExB r ExB

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


Fast imaging: evidence of asymmetry

HFS injectionexp ~ 20 µs

LFS injectionexp ~ 20 µs

HFS LFS

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


Interpretation of multi-diagnostic investigation

Particle transport in SOL : Particle transport in SOL :

- ExB convection of plasma “filaments”

51//// L usual flute mode paradigm //// L

- 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

Vr ~ 1% cS

V// ~ 100% cS

Vr ~ 1% cS

V// ~ 100% cS

II


SteadySteady--statestate picturepicture snapshotsnapshot MagneticMagnetic reconstructionreconstruction

LCFSLCFS

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 ( + local conditions ( * , * , P P ) similar to SOL) similar to SOL

--> emissive ring in the confined region (r/a ~0.5 )--> emissive ring in the confined region (r/a ~0.5 )

Again,Again, (largest)(largest) field alignedfield aligned structures only on thestructures only on the Low Field SideLow Field Side

filaments filaments k k//// > 0 + open / closed field lines > 0 + open / closed field lines

II


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 machinescoherent with other evidencesconciliate apparent incoherenciesL-mode : LIMITER DIVERTOR


Summary Experimental investigation of edge transport :

About diagnostics : - interpretation of experimental data

improving probe geometry for // flow measurements improving probe geometry for // flow measurements

- multi-diagnostic consistency

critical issues on the spatial sampling of fluctuationscritical issues on the spatial sampling of fluctuations

projection artifacts with visible imagingprojection artifacts with visible imaging

local & global measurementslocal & 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


Ionization source in the SOL

50-50 0R (cm)

-60

-40

-20

0

20

40

60

Z (c

m)

0

0.5

1

1.5

2

(1022)

50-50 0R (cm)

-60

-40

-20

0

20

40

60

Z (c

m)

0

0.5

1

1.5

2

(1022)

• Monte-Carlo simulation of recycling on main limiter : EIRENE simulation

• 3D domain ( toroidal symmetry)

• Initial input (experiment) : ion fluxes @ limiter plates (from Mach probe) ne + Te + Ti profiles (SOL + confined region)

• Complete database for Deuterium atomic reactions

• Self-consistent matter balance


*//// )( vnvnvn E

rrFlux balance :

)( nv E

Transversal drifts in SOL flux balance

Simplified flux balance :

rrS

raS Bc

EqMcn

////

|M//| ~ 1

- large aspect ratio-Er independent of


Pressure conservation

//2

//22 vvvn cn vn rrS////

radial transfer of // momentum

Spatial mapping of r

spatial mapping of & //vrv

Computable Reynolds stress

P/P < 15 %

! But only linear term !

Validation with simulationSOLEDGE2D G. Ciraoloa & H. Bufferand

(only viscosity)

P/P < 10 %


Flow reversal experiment

M||

BT

IP

M||

BT

IP

probe

M//r

LFSHFS

l//

LFSHFS

probe

M//

r

l//


3D filaments : revisiting momentum transfer

Vr ~ 1% cS

V// ~ 100% cS

Vr ~ 1% cS

V// ~ 100% cS

LIM

ITE

R

vr

r

l//

FIRST WALLFIRST WALL

LIM

ITE

R

LFSHFS

v//

ttrtr vvvv //// Issue in understanding SOL flow effect on core rotation

transfer of v//

1-ms30

rV

1-ms 300

rV

rv

• // dynamic of a single “filament”

// front expansion ? Scv //

coupling with local ExB fluctuations along the field line ?

computable from previous results

average on flux surface : NO RESIDUAL TRANSFER


SOL flow and core rotation M||

BT

IP

co-Ip

M||

BT

IP

ct-Ip

co-IP

ct-IP

flow reversal in SOL plasma for similar core plasma

change in core velocity fields

V V


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


List of contributionsFirst author publications :

N. Fedorczak, J.P. gunn, Ph. Ghendrih, P. Monier-Garbert, A. PocheauFlow generation and intermittent transport in the scrape-off layer of the tore Supra tokamakFlow generation and intermittent transport in the scrape-off layer of the tore Supra tokamakJournal of Nuclear Materials 390–391 (2009) 368–371Journal 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 Experimental investigation on the poloidal extent of the turbulent radial flux in tokamak scrape-off layerscrape-off layerJournal of Nuclear Materials (2010)Journal of Nuclear Materials (2010)

Oral contribution to international conferences :

Ballooned like transport in the SOL of Tore Supra tokamak : evidences and propertiesBallooned like transport in the SOL of Tore Supra tokamak : evidences and propertiesTransport Task Force meeting (TTF2009) San Diego Transport Task Force meeting (TTF2009) San Diego

Poloidal mapping of turbulent transport in SOL plasmasPoloidal mapping of turbulent transport in SOL plasmasPlasma Surface Interaction meeting (PSI2010) San Diego Plasma Surface Interaction meeting (PSI2010) San Diego

A first comparison between probes, fast imaging, and Doppler backscattering synchronous A first comparison between probes, fast imaging, and Doppler backscattering synchronous measurements of edge turbulence in Tore Suprameasurements of edge turbulence in Tore SupraEuropean Plasma Society (EPS2009) Sofia European Plasma Society (EPS2009) Sofia (F. Brochard & N. Fedorczak) (F. Brochard & N. Fedorczak)


Many thanks toTore Supra pilots

Physicists

Technical support :

F. Saint-Laurent, P. Hertout, D. douai, Ph. Moreau F. Saint-Laurent, P. Hertout, D. douai, Ph. Moreau

Jamie Gunn, P. Hennequin, L. Vermare, P. Monier-Garbet, P. Devynck, F. Jamie Gunn, P. Hennequin, L. Vermare, P. Monier-Garbet, P. Devynck, F. ClairetClairetC. Reux, D. Villegas, M. Kocan, X. Garbet, Ph. Ghendrih, Y. Sarazin, P. C. Reux, D. Villegas, M. Kocan, X. Garbet, Ph. Ghendrih, Y. Sarazin, P. Tamain Tamain

J.Y. Pascal, B. Vincent, F. Leroux, T. Alarcon, N. Seguin, V. J.Y. Pascal, B. Vincent, F. Leroux, T. Alarcon, N. Seguin, V. NegrierNegrier

friendsMatthieu, Sara, Sebastien, Vincent, Yannick, Matthieu, Clement,Matthieu, Sara, Sebastien, Vincent, Yannick, Matthieu, Clement,

Sophie, Daniel, Gaëlle, Etienne, Cédric, Victor, Gwen, Ronan, Rémi, Matthieu,Sophie, Daniel, Gaëlle, Etienne, Cédric, Victor, Gwen, Ronan, Rémi, Matthieu, Mélanie, François, Joao, Tom, Magwa, Sparrow,Mélanie, François, Joao, Tom, Magwa, Sparrow,

Mélissa, Mai, Caro, Clemence, Dimitri,Mélissa, Mai, Caro, Clemence, Dimitri, Vanessa, Julien, Lana, Alexis, Uron, Suk-ho, TimoVanessa, Julien, Lana, Alexis, Uron, Suk-ho, Timo

G. Ciraolo, L. Isoardi H. Buferand, E. Serre, G. Ciraolo, L. Isoardi H. Buferand, E. Serre, G. Bonhomme, F. Brochard, M. Farge, R. Nguyen, A. Pocheau, G. G. Bonhomme, F. Brochard, M. Farge, R. Nguyen, A. Pocheau, G.

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