Evidence for and Implications of Zonal CMTFO Flows as … · CMTFO G.R. Tynan, 2nd Asia-Pacific...

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

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

•  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

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

<vx vy>~~

∇T, ∇n...

<vx p>~~Transport

Ref: Itoh PoP06

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

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)

GAM Also Observed in Edge Region

GAM �

˜ n f( ) 2

Vθ f( ) 2

DIII-D

DIII-D REF: McKee PoP 2001

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

DIII-D McKee IAEA 2006, PPCF 2006

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

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

Lead Actors: Turbulence, ZF & Mean Shear Flow

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)

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

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

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

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

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

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

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

HL-2A Zhao et al, PPCF

Does GAM or ZF Shearing Rate Become Significant?

ZF Drive Increases as Plasma Heating Increases

M. Xu, Accepted PRL 2012

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

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

Strong Stress Oscillations in LC Regime

PRELIMINARY! (a) (b)

DIII-D

• 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?

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?

Turbulence Recovery in LC Regime Gives Energy Input Rate

Manz et al, submitted 2012

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

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

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

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

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

Picture is Consistent w/ Earlier Work

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

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?

Thank you for your attention

Evidence for and Implications of Zonal CMTFO Flows as … · CMTFO G.R. Tynan, 2nd Asia-Pacific...

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