UCSD-PRC China Collaborations

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G.R. Tynan, 6th US-PRC MFE Research Workshop, UC San Diego, July 2012

Recent Results from and Plans for UCSD-China MFE Collaborations

G.R. Tynan UCSD

6th US-PRC MFE Research Workshop

July 2012 UC San Diego

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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Current & Future Research Foci

•  Trigger Physics for L-H Transition

• Origin of Intrinsic Toroidal Rotation

•  Long-pulse PMI in Confinement Devices

• Gas-cooled High Heat Flux Components

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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"

VExB

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

t

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

HIBP#1observation points

HIBP#2observation points

ExB flowEr

φctrφin

φout

Poloidal Crosssection 2

Er

Poloidal Crosssection 1

φctrφin

φout

ExB flow

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




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Strong Stress Oscillations in LC Regime

Boedo, EPS 2012 (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, accepted, PoP Aug 2012

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


EAST

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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

MODEL EAST


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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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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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Current & Future Research Foci

•  Trigger Physics for L-H Transition

• Origin of Intrinsic Toroidal Rotation

•  Long-pulse PMI in Confinement Devices

• Gas-cooled High Heat Flux Components

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PISCES-A w High Heat Flux Irradiation Stage

Steady-state Irradiation to ~5 MW/m2

Gas-cooled Integrated target

Opportunity for Collaboration w/ EAST/ASIPP

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Thank you for your attention

Documents

UCSD-PRC China Collaborations