Evidence for and Implications of Zonal CMTFO Flows as … · CMTFO G.R. Tynan, 2nd Asia-Pacific Transport Working Group, Chengdu China, May 2012 Evidence for and Implications of Zonal

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G.R. Tynan, 2nd Asia-Pacific Transport Working Group, Chengdu China, May 2012

Evidence for and Implications of Zonal Flows as the Trigger of the L-H transition

G.R. Tynan UCSD

2nd Asia Pacific Transport Working Group Meeting,

Chengdu, China 15-18 May 2012

Acknowledgement: P.H. Diamond, M. Xu, P. Manz, S. Thakur, N. Fedorczak, S. Mueller, C. Holland, J. Boedo, J. Myra, D.

Di’Pollito, L. Schmitz, G.S. Xu, B.N. Wan, H.Q. Wang, H.Y. Guo, J. Dong, K. Zhao, J. Cheng, W.Y. Hong, L.W. Yan

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Why Care About L-H Trigger Physics in 2012?

•  It is a KEY UNRESOLVED Physics Issue •  Operation in H-mode is THE BASELINE

Operational Scenario for ITER •  Empirical Thresholds are Highly

Uncertain –  Can We Get Into H-mode When We Want

To?

•  Our H-mode Scenarios Depend on Reduced Wall Recycling –  Can We Maintain H-mode When We Want

It? –  Can We Avoid It if Necessary?

Here We Test Hypothesis that Turbulence/ZF/Mean Shear Flows Are Key Actors

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Nonlinear drift turbulence-zonal flow interactions"

Generation By vortex tilting

Damping by collisions Tertiary instability

Suppression of DW by shearing

Drift waveturbulence

Zonal flows

Shearing

Collisional flow damping

SUPPRESSNonlinear flow damping

energyreturn

DRIVE

<vx vy>~~

∇T, ∇n...

<vx p>~~Transport

Ref: Itoh PoP06

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Zonal flows exist on closed flux surfaces

GAM?!Z. F.!

-0.01 -0.005 0 0.005 0.01

P E (a.u

.)

ω/Ωi

-1

-0.5

0

0.5

1

10 11 12 13 14

C (r 1,r 2)

r2 (cm)

r1=12cm

Radial distance

CHS Dual HIBP System

90 degree apart

Er(r,t)

Fujisawa, PRL 2004

High correlation on magnetic surface, Slowly evolving in time, Rapidly changing in radius.

Er(r,t)

21

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GAM Also Observed in Edge Region

GAM �

˜ n f( ) 2

�

Vθ f( ) 2

DIII-D

DIII-D REF: McKee PoP 2001

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A Transition from ZF (Core) to GAM (Edge) Occurs

DIII-D McKee IAEA 2006, PPCF 2006

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A Mean Shear Layer Naturally Exists at LCFS

On Open Field Lines we have

�

φpSOL (r) = φwall (r) + ΛshkTe (r)

∴

ErSOL (r) = −Λshk∇rTe (r) > 0

In Weakly Heated Core Plasma w/ Weak Flow Have

�

Er(r) = ∇r pion − v × Bw / weak flows thenEr(r) = ∇r pion < 0

TEXT Ritz PF’84

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Rapid Development of V and Mean Erad at L-H Transition

Groebner PRL 1990, Doyle Phys. Fluids-B 1991

Important: Transient in Vtheta FIRST, then Grad-P Build UP

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Lead Actors: Turbulence, ZF & Mean Shear Flow

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2 Predator/1Prey Model Predicts Intermediate State

Observed First in TJ-II by Estrada et al, EPJ 2009 Similar (but not identical) Observations in

AUG (Conway, PRL ‘11) EAST (Xu, PRL’11) DIII-D (Schmitz, PRL’12)

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Examples of L-I-H Transition Sequence

DIII-D Schmitz et al, PRL’12 TJ-II, Estrada, EPL, 2010

TJ-II Estrada, EPL 92, 35001 (2010) TJ-K Manz, Phys. Rev. E 82, 056403 (2010) NSTX Zweben, Phys. Plasmas 17, 102502 (2010) ASDEX-U Conway, Phys. Rev. Lett. 106, 065001 (2011) EAST Xu, Phys. Rev. Lett. 107, 125001 (2011) DIII-D, Schmit, PRL 2012

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GAM Amplitude & Mean ExB Shear INCREASE in L-‐> I Mode

ASDEX-‐UG Conway, IAEA-CN-180/EXC/7-1 (2010)

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Key Missing Quantity: Nonlinear Energy Transfer Between Turbulence and ZFs

Can Measure P w/ Suitable Spatio-temporal Diagnostics (Sanchez, ‘05, M. Xu,’09, GS Xu, ‘09, Manz,’09

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Expected Signatures:

• NL Coupling into ZF (GAM) Should Increase w/ Heating in Fixed-point L-mode

•  Bifurcation into Limit Cycle Regime Accompanied by Onset of Stress LC’s

• Growing Importance of ZF Shearing as LCOs Grow and Approach H-mode

• Collapse of Turbulence, ZF and Onset of Mean Shear Flow

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• NL Coupling into ZF (GAM) Should Increase w/ Heating in Fixed-point L-mode




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GAM/ZF Amplitude Increase Strongly as PL-‐H is Approached

HL-2A Zhao et al, PPCF

Does GAM or ZF Shearing Rate Become Significant?

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ZF Drive Increases as Plasma Heating Increases

M. Xu, Accepted PRL 2012

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GAM & ZFs Compete for the Prey…

Total energy transferred within a turbulence characteristic time (25 microsecond was used) normalized by total turbulent energy.

M. Xu, Accepted PRL 2012

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• NL Coupling into ZF (GAM) Should Increase in Fixed-point L-mode




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Strong Stress Oscillations in LC Regime

PRELIMINARY! (a) (b)

DIII-D

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• NL Coupling into ZF (GAM) Should Increase in Fixed-point L-mode


• Growing Importance of ZF Shearing as LCOs Grow and Approach H-mode –  BUT HOW TO QUANTIFY?


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Nonlinear ZF Drive v. Linear Turbulence Drive is Key Dimensionless Parameter

Kim&Diamond’03

Linear Drive v. ZF Damping

KEY Dimensionless Parameter in Model:

In Experiment Look at the Nonlinear Production Term, P… But How to Estimate Energy Input Rate?

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Turbulence Recovery in LC Regime Gives Energy Input Rate

Manz et al, submitted 2012

EAST

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Evidence for Role of ZF Power Transfer in L-H Trigger

EAST

t (ms)

1 2 3 4 5

t (ms)

1 2 3 4 5

t (ms)

1 2 3 4 5

t (ms)

1 2 3 4 5

ZFs Peak BEFORE L-H Transition

Normalized ZF Production Peaks at ~1 Around L-H Transition… Similar Qualitative Behavior in DIII-D Expts

Manz, submitted 2012

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Turbulence & ZF Energy Exhibit One Orbit of LC Before the L-H Transition

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Predator-Prey Model Exhibits Similar Dynamics

Miki & Diamond, in prep.

t (ms)

1 2 3 4 5

Manz et al, submitted 2012

EAST L-H Transitions MODEL

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Physics of the L-H Transition Emerges:

•  Heating of Plasma Increases Turbulence, Decreases ZF damping

•  Eventually ZF becomes finite & begins extracting energy from turbulence

•  Further increases lead to ZF extracting nearly ALL energy from turbulence

•  Turbulent transport collapses •  Pressure gradient then builds before

turbulence can recover leading to increase in Mean Shear Flow (MSF)

• MSF Takes Over, Zonal Flow Dies Away

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Picture is Consistent w/ Earlier Work

Y.H. Xu, C. Yu et al, PRL 2000, Moyer, Tynan et al, PRL 2001

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Critical Implications

•  Threshold Depends on ZF Damping Rate –  Origin of Pthres~Density & Wall Cleanliness

Effects?

• No time to discuss details, but Ballooning Mode + Mag. & ExB Shear & Up-Down Asymm May Explain Favorable grad-BxB Drift Direction

• WHAT WILL HAPPEN TO H-MODE WHEN WALLS SATURATE (100s – 1000s) & RECYCLING RECOVERS TO UNITY?

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Thank you for your attention

Documents

Evidence for and Implications of Zonal CMTFO Flows as … · CMTFO G.R. Tynan, 2nd Asia-Pacific Transport Working Group, Chengdu China, May 2012 Evidence for and Implications of Zonal