Characteristics of the H-mode H and Extrapolation to ITER

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1 Characteristics of the H-mode H Pedestal and Extrapolation to ITER The H-mode Pedestal Study Group of the International Tokamak Physics Activity presented by T.Osborne 19th IAEA Fusion Energy Conference Lyon October 2002

2 Transport simulations set a minimum T PED divertor lifetime sets a maximum W ELM Required T PED depends on transport model stiffness Q GLF23 MM95 ITER, P = 40MW AUX n fixed ped ITER Goal Melting and ablation threshold requires < 1MJ/m 2 /ELM to divertor GLF Maximum Tolerable ELM size W ELM /W ped MM J. Kinsey P1-09 T ped (kev) ν e * A.Loarte EX/P1-08, A.Leonard EX/P3-06

3 Pedestal and ELM characteristics from understanding of edge stability and H-mode transport barrier width Edge Stability Peeling Ballooning Mode Model H-mode Transport Barrier Width Physics based and empirical scaling Ion orbit loss region? Particle source region? ITG turbulence suppression zone? Empirical Pedestal Pressure Scaling ELM Energy Loss Connection to stability model? Transport through H-mode barrier: J.G. Cordey CT/P-02

4 Intermediate n Peeling-Ballooning Mode Model of the Type I ELM Instability is Consistent With Observations P variation with shape in DIII-D, JT- 60U, and AUG consistent with edge peeling-ballooning stability ELM onset time consistent with predicted instability onset Fast growing low 1 < n < 30 modes are observed as Type I ELM precursors X 1.0 n = 5 q=6/5 7/5 8/5 0.5 DIII D NATIONAL FUSION FACILITY SAN DIEGO ρ

5 Both P PED And J φ PED Important in Peeling-Ballooning Mode Stability Boundary Higher J φ PED ( reduced shear) stabilizes high n ballooning modes (second stability) but drives intermediate n peeling modes P PED and J φ PED interact through J BOOT P.B. Snyder, TH/3-1 S J φ PED

6 Peeling-Ballooning Stability Plus Core Transport Simulations Sets Minimum Barrier Width Maximum Stable T ped (kev) T ped limits for ITER, n ped = cm -3 2nd stable Range of widths on DIII-D n=30 n=20 n=15 n= pedestal width/minor radius ( /a) P.B. Snyder, TH/3-1 ELITE code results for simplified equilibrium and Sauter model j Boot. Stability + temperature requirement for core confinement minimum transport barrier width. Existing experiments have widths in the required range STABILITY + Q=10 MIDPLANE /a = 2.5 % STABILITY + Q=10 MIDPLANE /a = 1 %

7 Transport barrier width scalings currently either do not have a strong physics basis or are in conflict with some part of the data set Physics based approach uses result that the H-mode transport barrier represents a region where velocity shear is sufficient to quench turbulence. Extent of source region of drive for velocity shear Ion orbit loss region Neutral particle source region Region where velocity shearing rate in absence of turbulence exceeds linear growth rate of most important instability Currently no simple physics based scaling matches the data from all tokamaks well more detailed comparisons are required Empirical scaling Difficult to apply with confidence

8 Physics based empirical scaling of can give a variety of statistically equivalent results Scaling Temperature Width based on DIII-D data only Scaling R β θ ρs ρ 2 ρrq 2 / 3 R 1/ 3 ε ρ θ Ion orbit loss 45 Neutral penetration 68 3 / 2 1/ n ped Physics Magnetic and flow shear stabilization Flow shear stabilization Diamagnetic stabilization T. Onjun, Phys. Plasmas Poloidal pressure σ (%)

9 Barrier width related to extent of flow shear drive from ion orbit loss? V 1/2 2(6ε/(1+ε)) ρ /a pi V jxb from return currents associated with loss of ions on orbits crossing the separatrix drives turbulence-suppressing flows Size of ion orbit loss region is about the width of a banana orbit 2 = 2 f T v TOT / Ω Pi 6ε /(1 + ε ) ρ Pi

10 (ρ P ) inconsistent results on some tokamaks DIII-D Divertor Pumping Exp. PED e (T ) PED 1.0 e (T ) 0.2 PED δ e (cm) CMOD data does not scale with ρ P (p ) e PED TIME (ms) PED e (T ) 0.2 PED δ e (cm) PED (T ) e PED 0.5 (p ) e J.W. Hughes, Phys Plasmas, 9 (2002) HIGH PASS FILTER TIME (ms)

11 DENSITY WIDTH (m) Barrier width related to edge particle source? Hinton, Staebler 1 : Assuming velocity shear can take on any value consistent with radial force balance structure of particle and heat sources can control velocity shear and transport barrier width. Sep [ 2λ Ln ln( cγsepqsep)] H-mode L-mode Ohmic 1/ 2 D s (m 2 /s) D c (m 2 /s) E T i (ev) T i /T e DIII D NATIONAL FUSION FACILITY n e (ped) (10 19 m-3) SAN DIEGO λ = Vn / ne σv SEP Vn 2Ti / π m i [1] Hinton, F.L., Staebler, G.M., Phys. Fluids B 5, (1993), [4] Mahdavi, M.A., et al., Nucl. Fusion 42 (2002) 52 Neutrals acquire ion velocity at separatrix (or pedestal at low density) through charge exchange R. Groebner EX/C2-3 # occurences per bin Density and Temperature widths correlated Te / ne

12 Edge neutral source model predicts high separatrix temperature would be required for ITER Te,Ti /a CMOD /a Neutral Penetration Model Model accounts for large widths in JT60-U relative to DIII-D and CMOD Pellet fueling could expand barrier /a Neutral Penetration Model Stability and Q=10 Stability and Q= SEP T i ITER (kev)

13 Scaling based on ω ExB >γ L difficult due to uncertainties in γ L in pedestal region ω ExB ζ ζ cs cs a T e ~ > γ ~ / [ (,, ) ( ) ( * )] 2 L f S α q g Z EFF h v s ci a T Ω i 3/ 2 1/ 2 Ti ρ* s f ( S, α, q) g( Z EFF ) h( v* T = e * s ρ * does not organize data well Form of f uncertain near separatrix in highly shaped plasmas. Likely to be shape dependent. Scale length for variation in shear and also possibly of Z EFF and collisionality can be O( ) which could weaken ρ * dependence and introduce other dependencies. )

14 Empirical scaling of Difficult to reconcile large widths and ρ p dependence in JT60U with β P dependence in DIII-D and same relative widths between DIII-D and CMOD. Add density dependence to ρ p scaling plus shape terms. * = ρ κ * s ( B T (1 + δ ) / B 0.52 Ave p ε ) n 0.19 * G * = 0.12 ρ κ * s ( B T (1 + δ ) / B 0.57 Ave p R ) a n * G

15 Pedestal pressure scaling predicts edge pressure is consistent with ITER requirements but uncertainty is high PED 2 Ballooning mode like scaling for p : β / * = ε q α( ε, κ, δ, S) Departure of P-B modes from ballooning scaling determined in fit M. Sugihara, 57th Annual Meeting Phys. Soc. of Japan 100 T =5.3 kev ped ITER n ped =7x m - 3 O G P ped exp (kpa) 10 1 Fit with κ, δ, A, P RMSE=3.02kPa ASDEX-U JET JT60 β ped * * q (1 + δ ) (1 + κ ) = 0.12 A = ρ n 0.19 * G 0.38 * s κ ( B 0.98 T / B P (1 + δ ) ) 0.27± ε p ped = 10 4 * ρ pol / M ( n ped (1 + δ ) ) 1/ a a ( B κ p 3.81 ) A 2/ dp (( ) dr ( dp ( ) dr 0 P P 0 LH ) ) 0 4/ T B = 2µ Rq 2

16 ELM ELM size scaling Multi-machine comparison more consistent with ν dependence DIII-D more consistent with n/n GW Variation of W ELM at fixed parameters also a concern GLF Maximum Tolerable ELM size W ELM /W ped MM ν e * A.Loarte EX/P1-08 A.Leonard EX/P DIII D NATIONAL FUSION FACILITY SAN DIEGO W ELM / W PED PED e n /n GW GLF MM

17 Reduced W ELM /W PED at high n e, ν * correlated with reduced mode width from increased mode number and reduced ELITE CODE DIII D NATIONAL FUSION FACILITY SAN DIEGO Increasing ν * Sum of displacements for all m numbers n = 2 n = 5 n = ψ

18 Summary, Conclusions P-B model for edge stability is consistent with experiments and imposes constraints on pedestal height, which are strong functions of pedestal width,, and plasma shape. Diamagnetic effect may raise p substantially: P.B. Snyder, TH/3-1 Large uncertainties in scaling make it difficult to predict pedestal temperature based on a combination of transport barrier and stability physics. The connection between mode width and ELM size is perhaps a first step to understanding ELM energy loss and suggests similar size ELMs for ITER. SOL physics may play a role, A.Loarte EX/P1-08. Small (Grassy, Type II) ELM or ELM free (EDA, QH-mode) regimes may solve problem entirely There is still large uncertainty in the requirements for both ELM size and T PED in ITER due to differences in the predictions of the turbulent transport models

19 ELM size (energy loss) correlated with peeling-ballooning eigenmode radial in JT-60U high trangularity discharges Giant ELMs ~ 100 Hz, small amplitude grassy ELMs ~ Hz At intermediate δ and q 95 mixtures of giant and grassy ELMs Unstable edge modes in grassy elm discharges have narrow radial mode width (ELITE Code). Changes in radial width related to difference in q profiles LL. Lao, et. al, Nucl. Fusion, (2001).

20 Diamagnetic stabilization with simple models Pedestal β Nped [β ped /(I/aB)] Impact of ω * models on ITER pedestal stability ideal (no ω * ) local ω * model modified ω * model pedestal width/minor radius ( /a) Rotation and non-ideal effects expected to have significant impact Simple models give indication of the impact of diamagnetic effects Local γ MHD >ω *pi /2 Rogers & Drake suggested modification: 1/(1+1/k θ L p ) Simple models suggest significant stabilization, shift of most unstable mode to longer wavelengths (n~8-20)

21 ELM free H-mode with edge harmonic oscillation (EHO) has high H and no density accumulation. Counter Injection Low density with divertor pumping Large outer gap H89P to 2.4 β N to 2.9 β N H to PED Te /n GW QH-MODE ELM PHASE IN QH-MODE DISCHARGE TYPE I, LAST 20 % OF ELM CYCLE δ UPPER > TYPE III nped e /n GW