30 th eps, st. petersburg, 7-11 july, 2003m. bécoulet 1/32 30 th eps, st. petersburg, july 2003 m....

30thEPS, St. Petersburg, 7-11 July, 2003 M. Bécoulet 1/3230thEPS, St. Petersburg, July 2003 M. Bécoulet

Edge Localised Modes Physics and Edge Issues in Tokamaks.presented by Becoulet M.

G. Huysmans (1), Y. Sarazin (1), X.Garbet(1), Ph. Ghendrih (1), F. Rimini (1), E. Joffrin (1), Litaudon X. (1), P. Monier-Garbet (1) , J.-M. Ané (1), P. Thomas (1), A. Grosman (1),

(1) Association Euratom-CEA, CE Cadarache, F-13108 St. Paul-lez-Durance, France.V.Parail (2), H. Wilson (2), P. Lomas (2), P. deVries(2) , K.-D. Zastrow(2), G.F. Matthews (2), J. Lonnroth (2), S.

Gerasimov(2), S. Sharapov(2), M. Gryaznevich(2), G. Counsell(2), S.Fielding(2), A. Kirk(2), M. Valovic(2), R. Buttery(2) ,(2) Euratom/UKAEA Association, Fusion Culham Science Centre, Abingdon, OX14 3EA, UK.

G. Saibene (3), R. Sartori (3), A. Loarte (3) ;(3) EFDA Close Support Unit (Garching), 2 Boltzmannstrasse, Garching, DE.

A.Leonard (4), P. Snyder (4), L.L. Lao(4), P. Gohil(4), T.E.Evans(4), (4) General Atomics, 3550 General Atomics Court,P.O.Box 85608 San Diego,CA,U.S.A.

Y Kamada (5), A Chankin (5), N. Oyama(5), T.Hatae(5) ,N. Asakura(5),(5) Japan Atomic Energy Research Institute (JAERI), Japan

O. Tudisco (6), E. Giovannozzi(6) , F. Crisanti(6),(6) Associazione EURATOM-ENEA sulla Fusione, C.R. Frascati, Frascati , Italy

C. P.Perez (7), H. R. Koslowski(7) ,(7) Institut für Plasmaphysik, Forschungszentrum Julich, Germany

T.Eich(8), A. Sips(8), L. Horton(8) , P. Lang (8), A. Hermann (8), J. Stober(8), W. Suttrop(8), (8) Association Euratom-IPP, MPI fur Plasmaphysik, 2 Boltzmannstrasse, Garching, D-85748, Germany

P. Beyer(9),(9) UMR 6633PIIM CNRS-Université de Provence,F-13397 Marseille Cedex 20, France.

S. Saarelma(10),(10) Helsinki University of Technology, Euratom-TEKES Association, FIN-02015 HUT, Finland

R.A. Moyer (11)

(11) University of California, San Diego, La Jolla CA 92093,U.S.A. and contributors to JET-EFDA Workprogramme.

AssociationEuratom-Cea


1. Introduction. -High confinement scenarios for ITER and ELMs.

2. H-mode scenarios and ELMs (theory + experiment).-Ballooning-peeling linear MHD model.- Pedestal and SOL transport, non-linear models.-ELM size: role of density, triangularity, high q95, high p. -High confinement regimes with Type II ELMs for ITER?

3. Internal Transport Barrier (ITB) scenario and ELMs.

- Combined ITB+ ETB scenarios.

4. Active control of ELMs.-Edge ergodisation, edge current, pellets.

Outline.


ELM = plasma edge MHD instabilities typical for H-modes in tokamaks => periodic fast (200s) relaxations of edge pressure => energy to SOL =>divertor+wall.

D

Wdia

Te ped

ne ped

JET: Ph.Ghendrih JNM (2003)

divertor

JET: G. Saibene PPCF2002

ELM cycle: periodic loss of confinement

time(s)

after

after

before

before

DIII-D:- A. Leonard PPCF2002

ne=> convective

Te=> conductive

radius(m)


Type I : low fELM, high Pped=> high confinement,but large energy losses per ELM.

Type II : regimes in highly shaped plasmas, high Pped, (confinement ~like Type I ELMs), small edge MHD activity, but for narrow operational window.

Type III: (at low power or at high density): higher fELM, small energy losses per ELM, but lower Pped=> low confinement.

Experimental scaling for ELMs types

L-modeH-m

ode:Type I

IIType I

I

JET: Sartori R. PPCF2003 submitted

H-mod

e:Typ

e I

L-mode

L/H threshold ~0.45ne 0.75 BTR2 (MW)


ITER reference scenarios Q=Pfusion/Padd.~10(Aymar et al 2001) :

high confinement (H98y>1); high density (>0.8nGR), high

and

acceptable (material limits=melting, erosion,evaporation…=>reasonable divertor life-time) heat loads on the divertor target plates: WELM

ped<5-10MJ (if 60% goes to the divertor S~3m2 )(Federici PSI 2002).

ELMs are problematic for ITER.pr

essu

re

radius

ET

B

core

pedestal pressure(=confinement)is limited by MHD

H-mode scenario(or advanced regimesw/o ITB?)

heat

flu

x to

SO

L

radius

ITB

ITB scenario

ITB erosion by large ELMs

pres

sure

heat

flu

x to

SO

L

ET

B

ITB


plasma

Experiment evidence from many tokamaks: ballooning structure

MAST: G.Counsell 2002

Te, ne collapse on LFS

-Ballooning structure of ELMs=> collapse of Te, ne on the LFS.-Parallel SOL transport => divertor (~50% : T.Eich EPS2001 ); -SOL perpendicular turbulent transport (“tails”, “blobs”) => wall

Outboard D

MAST: A. Kirk 2003

wall

plasma edge

inboard outboard

beforeduringafter

SOL


Linear ideal MHD theory: ELMs=ballooning-peeling modes.

Linear MHD stability analysis (codes MISHKA, GATO, ELITE).

-Ballooning modes driven by pressure gradient => pedestal, outboard (=LFS), high n.-Peeling (kink) driven by edge current (+bootstrap) =>X-point, low n=1-4

-Coupled peeling-ballooning => LFS, pedestal, n~10-20 (JET).JET: M. Becoulet et al PPCF2002

jedge

ballooning-peeling: n=12

JET(MISHKA): G.Huysmans 9thEFPW 2001

0.8 1

Ped

esta

l sho

ulde

r

20

B

P2q0

Pee

ling

com

pone

nt


MISHKA: modes structure, growth rate, ~ etncritif crit ;

TELM () :

0loss

StP

PVPP////

M. Becoulet,G. Huysmans et al 2003

Los

ses

in th

e S

OL

:S

loss=

- P

///

before

after

Pressure collapse in ELM: non-linear modelling

Br (ergodisation)+V(convection)

0. 0.6 time (s)0.2 0.4

elm~200sdiffusion

ELM


Resistive ballooning turbulence (B=0, =0 ) modelling : periodic energy bursts through ETB. Estimations for “ELM” time ~250s! More development needed both with MHD + turbulence (DIII-D, BOUT-X.Xu et al

New J. of Phys. 2002)

(P.Beyer ,to be submitted PoP2003)

Turbulence modelling: ELMs?

SOLcore


ELM collapse on the LFS => inner/outer delay in D t delay~ // (ions) =2Rq95/Cs, ped . Increases with the density.

JET : A. Loarte et al PPCF2002

Particle transport in SOL to the inner and outer divertor.

OuterLFS

InnerHFS

ELM collapse

innerouter

LFS

HFS

JT-60U: A.Chankin, N. Oyama et alNF2002, PPCF 2001

dB/dt


Type I ELM time: divELM > ~ MHD

ELM

MHDELM ~ 150-300 s (JET),

similar in JT-60U, DIII-D, AUG~1ms. Not identified parametric dependence. Weak?

IR data

Energy into divertor is deposited with ion flux time //

ion => divELM

increases with the density.

JET: A.Loarte PPCF2002


Toroidal asymmetry of Type I ELM in JET (similar TCV: H. Reimerdes

NF1998). Propagation in electron diamagnetic direction: ~SOL// . Not

explained by linear MHD.

toroidal Mirnov coils

Toroidal “rotation” of ELM

JET(M.Becoulet, G. Saibene 2003)

Broken coils

Low nped High nped


What physics? ne => Te

ELM “size” decreases with the density.

What are the key factors to decrease ELM size keeping high confinement? Multi-machine experimental scaling: WELM/Wped decreases with with ne, ped (*ped,, Front

// … ).

ineoen~ETB

2/5eT~

//

-SOL transport?

-Pedestal transport?

A. Loarte PPCF 2002-MHD=>bootstrap current

2/3eT/

effZ~

// =2Rq95/Cs, ped

Not identified yet;

ee95

Rq

Log scale


MISHKA modelling for JET: diffusion of edge bootstrap current improves stability for low n peeling modes. Main difficulty: sensitivity of stability diagram to small changes in Te, ne, Jz profiles, no direct measurements of edge current.

JET(MISHKA): G.Huysmans 9thEFPW 2001

Edge bootstrap current decreases with density.

unsta

ble

stabl

e


As density increases pedestal width (less obvious on JET!), bootstrap current , mainly conductive losses T/T with densityModelling => Radial width of mode decreases =>Smaller ELMs?

DIII-D (ELITE: P.Snyder et al IAEA 2002)

ELM size =ELM affected area? Open question.

DIII-D (A. Leonard et al, PPCF-2002)


Transport modelling(TELM): smaller affected area = smaller ELMs?

TELM ( M. Becoulet et al 2003)

Large ELM area : WELM/Wped~3% Narrow ELM area: WELM/Wped~1.2%


H98

y

ne/nGR(%)

High triangularity (=> higher pedestal pressure => higher confinement (AUG, JT-60U, DIII-D, JET…)

JET(MISHKA): G.Huysmans 9th EFPW 2001JET: G. Saibene et al PPCF2002

Edge current

Pre

ssur

e gr

adie

nt

Low High

ELM size: role of plasma shaping=> improved MHD stability

ITER

stablestable

Similar results for AUG,JT-60U, DIII-D…

kink unstable

Ballooning unstable


High confinement regimes with small “grassy” ELMs recipe =>high magnetic shear: , high q95=3.5- 6, high p~2.

high p(~2 ) helps =>grassy” at q95=3.6 (in ITER~3)

JT-60U Y. Kamada et al PPCF2002

High triangularity (edge magnetic shear)=>“Grassy” ELMs in JT-60U


Type II ELMs in ASDEX-Upgrade.

Type II ELMs : =0.4 (Double Null is important!), q95>4.2, n/nGR~0.85-0.95(high density) , H98~1. Broadband MHD: n=3,<30kHz. Low heat load into divertor.Advanced scenario with Type II at high p.(0.8MA/1.7T, 10MW NBI)=0.4 (Double Null configuration)q95=3 (q0~1 to avoid saw-teeth)n/nGR~0.88, H 98-P~1.2-1.3, p=1.8, N=3.5Effect of high p?-Core confinement is improved (turbulence; bootstrap =>flat shear…) -ELMs Type II at lower q95 ~3.

AUG: A. Sips 9thEFPW 2001

To Double Null


ELM affected area decreases at high q95 +high for the same pressure profile. Double Null configuration increases edge shear even more.

GATO (for AUG) S. Saarelma et al, NF(2003)

Linear ideal MHD (GATO): ELM area is small for Type II ELMs

n=3

n=3


; q95=3.4, n/nGR~0.9-1.1, H97~1. High density (*~0.6-0.8!) => smaller Type I + Type II = broad band MHD <30kHz, n=8 (Washbroad resistive modes? Ch.Perez NF2003). SN and DN configurations were tried. Not enough factors JET to suppress Type I ELMs on JET? And for ITER? Other regimes w/o ELMs QH (DIII-D), EDA(C-mod)…

JET: G. Saibene et al PPCF(2002), see EPS 2003

ne=0.8nGR

ne=1.1nGR

JET: mixed Type I+Type II

D

D

Wdia

nene

Wdia


-Ideal MHD + transport models describe many experimental observations: ballooning structure, fast relaxation of Pped, MHD ELM time:ELM, frequency: fELM.

- Type I ELM MHD time (= typical pedestal crash time) is found ~150-300s for many machines. Parametric dependence is not identified yet.-ELM rise time on divertor target is correlated with ion // SOL transport. - Key factors to decrease ELM size?

-high pedestal density(collisionalty?); -high , high q95, high p;

-Regimes with benign Type II ELMs at high demonstrated ITER–like H97~1, n/nGR~0.8-0.9, but not for ITER-like parameters (*~0.05, p~1, q95~3)=> Low *, high power, high current…

Conclusions (I): ELMs in H-modes


Double barriers: ETB+ITB: high p with “grassy” ELMs.

High p~2, high q95~6.9, high => ITB+ETB with grassy ELMs => high performance (HHy2~1.2, n/nGR~0.6) + divertor heat load is reduced by factor 4-5 as compared to Type I ELMs.

JT-60U: Y. Kamada PPCF(2002)


D-III-D: P. Gohil 8th IAEA TCM2001

Quiescent Double Barrier =ITB+QH-mode without Type I ELMs on DIII-D (bN=3.5, wide range of q95, ). But : counter NBI injection, nped~0.1nGR. Interesting from the point of view: low * pedestal.

QDB


Usually Type I ELMs are not compatible with large ( ITB> 0.5) ITBs in JET, DIII-D: ITB erosion by Type I ELMs. If no pure Type II regimes => small Type III ELMs +ITB (=improved core confinement to compensate poor edge confinement). But how to keep Type III edge?

JET: M. Becoulet PPCF(2002)

Type IIIType I

ITB+Type I ELMs ? Type III ELMs?

Te (ECE)wall

plasma centre


Suggestion from theory: perturbation from ELM propagates inside => fast avalanche-like transport after an ELM: inward –outward turbulent fluxes. Why ITB is affected? Slow ( confinement) erosion of ITB, not MHD collapse! Rotation shear is affected ? Mechanism is unknown.

JET: Y. Sarazin PPCF(2002)

before 1st ELM

before 2nd ELMsteep gradients

Avalanche

Average profile

Steeper gradient=> unstable

Perturbation from Type I ELM propagates to ITB region?

SOLcentre

pres

sureITB


Main difficulty for ITB scenario at high ~0.5 is Type I ELMs avoidance. JET 2003: ITBs (3.4T/1.5MA) with Type III edge with D2: n/nGR~0.7, H98y~1.3, bN~1.8, p~1.5 , q95~7, lasts~ 6s.

JET: M. Becoulet , P. Lomas, O. Tudisco, F. Rimini, K.-D. Zastrow et al

High triangularity ITB on JET.


JET: M. Becoulet et al (2003)

JET: F.Rimini et al(2003)

Higher density0.7 nGR at HT(compared to 0.4nGR LT(but H89 = 2 (at LT)=>1.7(at HT) . Future => larger ITB : ITB>0.5=> performance, higher p, lower q95.

High triangularity=>higher density

High ITBs


-Combined regimes with ITB and ETB: ITB with “grassy” ELMs at high triangularity, high q95,

high p were demonstrated in JT-60U. ITB+ETB w/o ELMs : QDB in DIII-D (but counter NBI,

low n/nGR~0.1)

-High triangularity ITBs (~0.5, n/nGR~0.7, H98y~1.3, bN~1.8, bp~1.5, q95~7 ) with Type III ELMs were demonstrated on JET.

Conclusions(II): ELMs in ITBs

Active control of ELMs: -gas puffing;-impurity (increased Prad=> control Te,ped, but impurity accumulation?)

-edge current (Ip ramp-up, -down experiments => support peeling-ballooning

picture of ELMs, but very Pped, dIp/dt dependent, large res ITER)-edge ergodisation,-pellets…


External control coils Br(t) => edge ergodisation: <crit, or artificial ELMs. Compatibility with high confinement regimes?

COMPASS-D: S. Fielding et al EPS2001TCV: A. Degeling et al 2003

R. Moyer,T. Evans : DIII-D (C-coils) EPS2002

Br

Br

MaxBr

MaxBr

ELMs control by Brexternal?

More planned in 2003

See G. Jackson , EPS 2003 Friday -P-4.47


Pellets => increase of *, artificial ELMs are similar to natural.

Pellets.

ASDEX-Upgrade: P. Lang (EPS2002)see also this conference

W/o pellets: ~ 3Hz large compound ELMs

With pellets: 20 Hz smaller Type I ELMs


(towards ITER integrated scenario) 1. Key factors to decrease Type I ELM size:

-high , high q95, high p=> Type II ELMs for ITER?-increase pedestal density (*, //

ion,..?) => understanding of SOL energy and particles transport during an ELM is missing for the

definitive predictions for ITER.2. H-modes and combined advanced scenarios (with and w/o ITBs) at high triangularity high density with small ELMs demonstrated ITER –like performance (H97y>1, n/nGR~0.7-0.9) , but for the moment not for ITER-like parameters : *~0.05, p~1, q95~3 (H-mode); q95~4-5(ITB-scenario). Aim: high current, high power, low pedestal collisionality regimes!

3. Active control of ELMs is progressing => should demonstrate the compatibility with high confinement regimes for ITER.

Conclusions


increases with density => if < crit., no ELMs! , (first

demonstrated with JETTO: V. Parail EPS2001). But in experiment Type I=> Type III transition with ne increase, low confinement.TELM: M. Becoulet et al 2003

before

after

ETB

Transport through ETB increases with density=>smaller ELMs


Usually Type I ELMs are not compatible with large ( ITB> 0.5) ITBs in JET, DIII-D: ITB erosion by Type I ELMs. If no pure Type II regimes => small Type III+ITB(improved core confinement) ?

JET: M. Becoulet PPCF(2002)

Type IIIType I

ITB+Type I ELMs ? Type III ELMs?

Te (ECE)wall

plasma centre

JET: R.Sartori +M. Becoulet PPCF 2002

ITBs

Type IIIStandard H-

modes

Type I

L-mode


55599

55601

Tped

nped(55601,55599)

JET: Becoulet M. et al 2003

dithering

larger Type I ELMs!Type I

Edge current (Ip ramp-up):1)first improve stability; 2)then destabilise peeling modes: (when kink unstable): Type III or dithering L-mode. The result is very sensitive to edge Te, ne, dIp/dt…res for ITER?

Ip ramp-up

Ip ramp-down

current

Balloonin

g

unstable

Pre

ssur

e gr

adie

nt

Ip ramp-upIp ramp-down

Low n kink

unstable

n=14-22

(similar results MAST : Gryasnevich M. et al 2002; COMPASS-D, S. Fielding EPS2001 )

Edge current: Ip ramps, drive?

30 th eps, st. petersburg, 7-11 july, 2003m. bécoulet 1/32 30 th eps, st. petersburg, july 2003 m....

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