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

Association Euratom-Cea. Edge Localised Modes Physics and Edge Issues in Tokamaks. presented by Becoulet M.

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

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  1. AssociationEuratom-Cea 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.

  2. Outline. • 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 bp. • -High confinement regimes with Type II ELMs for ITER? • Internal Transport Barrier (ITB) scenario and ELMs. • - Combined ITB+ ETB scenarios. • Active control of ELMs. • -Edge ergodisation, edge current, pellets.

  3. ELM cycle: periodic loss of confinement Da Wdia Te ped ne ped ELM = plasma edge MHD instabilities typical for H-modes in tokamaks => periodic fast (200ms) relaxations of edge pressure => energy to SOL =>divertor+wall. DIII-D:- A. Leonard PPCF2002 JET:Ph.Ghendrih JNM (2003) JET: G. Saibene PPCF2002 Dne=> convective before after DTe=> conductive before after radius(m) time(s) divertor

  4. Experimental scaling for ELMs types 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. JET: Sartori R. PPCF2003 submitted H-mode:Type I Type II H-mode:Type III L-mode L-mode L/H threshold ~0.45ne 0.75 BTR2 (MW)

  5. ELMs are problematic for ITER. H-mode scenario (or advanced regimes w/o ITB?) ITB scenario ETB ITB ETB heat flux to SOL ITB core heat flux to SOL pressure pressure pedestal pressure (=confinement) is limited by MHD ITB erosion by large ELMs radius radius ITER reference scenarios Q=Pfusion/Padd.~10(Aymar et al 2001) : high confinement (H98y>1); high density (>0.8nGR), high d=0.5 and acceptable (material limits=melting, erosion,evaporation…=>reasonable divertor life-time) heat loads on the divertor target plates: DWELMped<5-10MJ (if 60% goes to the divertor S~3m2 )(Federici PSI 2002).

  6. Experiment evidence from many tokamaks: ballooning structure before during after SOL outboard -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 MAST: G.Counsell 2002 MAST: A. Kirk 2003 Te, ne collapse on LFS Outboard Da wall plasma plasma edge inboard

  7. ballooning-peeling: n=12 Linear ideal MHD theory: ELMs=ballooning-peeling modes. jedge 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(MISHKA): G.Huysmans 9thEFPW 2001 JET: M. Becoulet et al PPCF2002 Peeling component Pedestal shoulder 1 0.8 

  8. Pressure collapse in ELM: non-linear modelling before Losses in the SOL: Sloss= - P/t// after • MISHKA: modes structure, growth rate, ~ egt : g2~n(a-acrit) if a>acrit ; • TELM (a) : dBr (ergodisation)+dV(convection) M. Becoulet,G. Huysmans et al 2003 ELM diffusion telm~200ms 0. 0.6 time (s) 0.2 0.4

  9. Turbulence modelling: ELMs? Resistive ballooning turbulence (dB=0, dF=0 ) modelling : periodic energy bursts through ETB. Estimations for “ELM” time ~250ms! 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) SOL core

  10. Particle transport in SOL to the inner and outer divertor. inner outer HFS LFS ELM collapse on the LFS => inner/outer delay in Da:Dt delay~ t// (ions) =2pRq95/Cs, ped . Increases with the density. JET : A. Loarte et al PPCF2002 JT-60U: A.Chankin, N. Oyama et al NF2002, PPCF 2001 dBq/dt ELM collapse Outer LFS Inner HFS

  11. Type I ELM time: tdivELM > ~ tMHDELM tMHDELM ~ 150-300 ms (JET), similar in JT-60U, DIII-D, AUG~1ms. Not identified parametric dependence. Weak? Energy into divertor is deposited with ion flux time t//ion => tdivELM increases with the density. JET: A.Loarte PPCF2002 IR data

  12. Toroidal “rotation” of ELM Toroidal asymmetry of Type I ELM in JET(similar TCV: H. Reimerdes NF1998).Propagation in electron diamagnetic direction: ~tSOL// . Not explained by linear MHD. JET(M.Becoulet, G. Saibene 2003) toroidal Mirnov coils Broken coils F=3° Low nped High nped

  13. ELM “size” decreases with the density. What are the key factors to decrease ELM size keeping high confinement? Multi-machine experimental scaling: DWELM/Wped decreases with with ne, ped (n*ped,, tFront// … ). What physics? ne => Te A. Loarte PPCF 2002 -MHD=>bootstrap current -Pedestal transport? t// =2pRq95/Cs, ped -SOL transport? Not identified yet Log scale

  14. Edge bootstrap current decreases with density. 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 stable unstable

  15. ELM size =ELM affected area? Open question. As density increases pedestal width (less obvious on JET!), bootstrap current , mainly conductive losses DT/T with density Modelling => Radial width of mode decreases =>Smaller ELMs? DIII-D (ELITE: P.Snyder et al IAEA 2002) DIII-D(A. Leonard et al, PPCF-2002)

  16. Transport modelling(TELM): smaller affected area = smaller ELMs? TELM ( M. Becoulet et al 2003) Narrow ELM area: DWELM/Wped~1.2% Large ELM area : DWELM/Wped~3%

  17. ELM size: role of plasma shaping=> improved MHD stability H98y ne/nGR(%) High triangularity (d) => higher pedestal pressure => higher confinement (AUG, JT-60U, DIII-D, JET…) JET: G. Saibene et al PPCF2002 JET(MISHKA): G.Huysmans 9th EFPW 2001 Low d High d Ballooning unstable ITER Pressure gradient stable stable kink unstable Edge current Similar results for AUG,JT-60U, DIII-D…

  18. High triangularity (edge magnetic shear)=>“Grassy” ELMs in JT-60U High confinement regimes with small “grassy” ELMs recipe => high magnetic shear: d>0.5-0.6, high q95=3.5- 6, highbp~2. JT-60U Y. Kamada et al PPCF2002 high bp(~2 ) helps =>grassy” at q95=3.6 (in ITER~3)

  19. Type II ELMs in ASDEX-Upgrade. Type II ELMs : d=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 bp. (0.8MA/1.7T, 10MW NBI) d=0.4 (Double Null configuration) q95=3 (q0~1 to avoid saw-teeth) n/nGR~0.88, H 98-P~1.2-1.3, bp=1.8, bN=3.5 Effect of high bp? -Core confinement is improved (turbulence; bootstrap =>flat shear…) -ELMs Type II at lower q95 ~3. AUG: A. Sips 9thEFPW 2001 To Double Null

  20. Linear ideal MHD (GATO): ELM area is small for Type II ELMs ELM affected area decreases at high q95 +high d for the same pressure profile. Double Null configuration increases edge shear even more. GATO (for AUG) S. Saarelma et al, NF(2003) n=3 n=3

  21. JET: mixed Type I+Type II d~0.5; q95=3.4, n/nGR~0.9-1.1, H97~1. High density (n*~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? Otherregimes w/o ELMs QH (DIII-D), EDA(C-mod)… JET: G. Saibene et al PPCF(2002), see EPS 2003 ne=0.8nGR Da Da ne=1.1nGR Wdia Wdia ne ne

  22. Conclusions (I): ELMs in H-modes • Ideal MHD + transport models describe many experimental observations: ballooning structure, fast relaxation of Pped, MHD ELM time:tELM, frequency: fELM. • - Type I ELM MHD time (= typical pedestal crash time)is found ~150-300ms 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 d, high q95, high bp; • -Regimeswith benign Type II ELMs at high d demonstrated ITER–like H97~1, n/nGR~0.8-0.9, but not for ITER-like parameters (n*~0.05, bp~1, q95~3)=> Low n*, high power, high current…

  23. Double barriers: ETB+ITB: high bp with “grassy” ELMs. High bp~2, high q95~6.9, high d~0.5 => 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)

  24. QDB Quiescent Double Barrier =ITB+QH-mode without Type I ELMs on DIII-D (bN=3.5, wide range of q95, d). But : counter NBI injection, nped~0.1nGR. Interesting from the point of view: low n* pedestal. D-III-D: P. Gohil 8th IAEA TCM2001

  25. ITB+Type I ELMs ? Type III ELMs? Usually Type I ELMs are not compatible with large (rITB> 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? Type I JET: M. Becoulet PPCF(2002) Type III wall Te (ECE) plasma centre

  26. Perturbation from Type I ELM propagates to ITB region? JET: Y. Sarazin PPCF(2002) before 1st ELM before 2nd ELM Suggestion from theory: perturbation from ELM propagates inside => fast avalanche-like transport after an ELM: inward –outward turbulent fluxes. Why ITB is affected? Slow (tconfinement) erosion of ITB, not MHD collapse! Rotation shear is affected ? Mechanism is unknown. ITB pressure Steeper gradient => unstable centre SOL

  27. High triangularity ITB on JET. Main difficulty for ITB scenario at high d~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, bp~1.5, q95~7, lasts~ 6s. JET: M. Becoulet , P. Lomas, O. Tudisco, F. Rimini, K.-D. Zastrow et al

  28. High triangularity=>higher density Higher density: 0.7 nGR at HT(d~0.5) compared to 0.4nGR LT(d~0.2), but H89 = 2 (at LT)=>1.7(at HT) . Future => larger ITB : rITB>0.5=> performance, higher bp, lower q95. JET: M. Becoulet et al (2003) JET: F.Rimini et al(2003) High d ITBs

  29. Conclusions(II): ELMs in ITBs -Combined regimes with ITB and ETB: ITB with “grassy” ELMs at high triangularity, high q95, high bp 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 (d~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. 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, largetres ITER) -edge ergodisation, -pellets…

  30. ELMs control by dBrexternal? dBr=0 dBr=0 Max dBr Max dBr External control coils dBr(t)=> edge ergodisation: a<acrit, or artificial ELMs. Compatibility with high confinement regimes? R. Moyer,T. Evans : DIII-D (C-coils) EPS2002 COMPASS-D: S. Fielding et al EPS2001 TCV: A. Degeling et al 2003 See G. Jackson , EPS 2003 Friday -P-4.47 More planned in 2003

  31. Pellets. Pellets => increase of n*, artificial ELMs are similar to natural. With pellets: 20 Hz smaller Type I ELMs ASDEX-Upgrade: P. Lang (EPS2002) see also this conference W/o pellets: ~ 3Hz large compound ELMs

  32. Conclusions (towards ITER integrated scenario) 1. Key factors to decrease Type I ELM size: -high d, high q95, high bp=> Type II ELMs for ITER? -increase pedestal density (n*, t//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 : n*~0.05, bp~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.

  33. Transport through ETB increases with density=>smaller ELMs increases with density => if a < acrit., 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

  34. ITB+Type I ELMs ? Type III ELMs? JET: R.Sartori +M. Becoulet PPCF 2002 ITBs Standard H-modes Type I Type III L-mode Usually Type I ELMs are not compatible with large (rITB> 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 I Type III wall Te (ECE) plasma centre

  35. Edge current: Ip ramps, drive? n=14-22 Ballooning unstable Ip ramp-up Pressure gradient Ip ramp-down Low n kink unstable current JET: Becoulet M. et al 2003 • Edge current (Ip ramp-up): • 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…tres for ITER? Ip ramp-up 55601 55599 Ip ramp-down larger Type I ELMs! Type I dithering nped(55601,55599) Tped (similar results MAST : Gryasnevich M. et al 2002; COMPASS-D, S. Fielding EPS2001 )

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