CMTFO Recent Progress and Open Issues in Edge Turbulence and Transport

G.R. Tynan UCSD

EU-US TTF Meeting Cordoba, Spain

September 7-10 2010

Aknowledgement: to numerous colleagues who have shared their most

recent results and provided insights useful for this talk

CMTFO

Main Thesis of the Talk

•  Experiments Show that both Parallel and Perpendicular Dynamics are Crucial to Edge & SOL Transport

• An Emerging Picture of Key Observations is Presented

•  The Results Suggest that a Model Combining the DWT-ZF Paradigm of the Core with Equilibrium ExB and Parallel SOL Flows is Needed.

CMTFO

Key Observations

•  DWT - ZF/GAMs Dynamics Directly Observed •  ES (low-beta) & EM (finite beta) Intermittent

Structures at LCFS & in SOL •  These Can Drive Mean Parallel SOL Flows •  Mean ExB Shear Naturally Exists at the LCFS & Act

on Turbulence •  Turbulent Stresses Can Reinforce Parallel & Perp

Flows •  Mean Flows Can Also Affect Turbulent Stresses •  Neutral Recycling Can Damp ExB Shear Flows, ZF/

GAMs

CMTFO

Key Observations

•  DWT - ZF/GAMs Dynamics Directly Observed •  ES (low-beta) & EM (finite beta) Intermittent

Structures at LCFS & in SOL •  These Can Drive Mean Parallel SOL Flows •  Mean ExB Shear Naturally Exists at the LCFS & Act

on Turbulence •  Turbulent Stresses Can Reinforce Parallel & Perp

Flows •  Mean Flows Can Also Affect Turbulent Stresses •  Neutral Recycling Can Damp ExB Shear Flows, ZF/

GAMs

CMTFO 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

CMTFO

August 2008

Zonal flows exist on closed flux surfaces

GAM?!Z. F.!

-0.01 -0.005 0 0.005 0.01

P E (a.u

.)

!/"i

-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

CMTFO

August 2008

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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Turbulence Drive of ZF Confirmed in Lab Plasma

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Image of Radially Sheared m=0 Zonal Flow

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( ) θθθ µν iiiiior VVvvrrr

222

~~1 ∇+−=∂∂

Mea

sure

d Re

ynol

ds st

ress

ZF  Drive  from  Turbulent  Azimuthal  Momentum  Balance  

Tynan et al April 2006 PPCF Holland et al, PRL’06

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Flow Profile Consistent with Turbulent Momentum Balance

Tynan et al, April 2006 PPCF, , Holland et al, PRL 2006

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13

•  3-Point Correlation Measurement in TJ-K

•  HW Model: •  C >> 1 adiabatic limit (n = ) •  C = 1 experimental value •  C = 0 hydrodynamic limit (n, = decoupled)

Experimental Tests of N.L. Spectral Energy Transfer

k1

k

k2

�

C(δx1,δx2 )⇒ S(k1, k2 )

CMTFO

14

Potential (Energy)

Density (Enstrophie)

Energy transfer in TJ-K

Spectral power transfer of potential (upper) and density fluctuations (lower graphs) from Hasegawa-Wakatani simulations at C=2 (left) and C=1 (middle) and the experimental data (right). (see next slide)

P. Manz et al, PPCF 2008

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Self-Consistent Picture of DWT Saturation Emerging

DWT   Unstable   in   Intermediate  frequency   and   wavenumber  range  

Nonlinear energy transfer moves energy to other spatio-temporal scales

Kine;c   energy   transfer   to   large  scale   sheared   ZF   occurs   and   is  observable  

Xu, PoP’10

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 Kine%c  energy  is  transferred  from  intermediate  frequency  regions  to  both  low  and  high  frequency  regions.

Net Energy Transfer in Linear Device

gaining  energy  

losing  energy  

M. Xu et al PoP’10

CMTFO Turbulence Saturation Physics Confirmed

•  Measure Spectra & Net Nonlinear Transfer Rates

•  Define “Effective Growth Rate” as

•  Compare with calculated linear growth/damping rates

•  SUGGESTS HAVE CONSISTENT PICTURE OF FREE ENERGY GROWTH/DISSIPATION & N.L. TRANSFER!

M. XU et al, PoP’10

�

γ eff (k) = −Tu(k)u⊥2 (k)

CMTFO

August 2008

Regulation of particle transport by ZF"

ZF

HIBP on CHS Fujisawa, PPCF 2006

Time (ms)"

-1

0

1

40 50 60 70

!"

(V)

time (ms)

150

100

50

0

f (kH

z)

0"

150"

f (kH

z)"

!"

=

1 B

E!

,"n"

CMTFO

August 2008

Regulation of transport by ZF"

HIBP on JFT-2M Ido, NF 2006

Time (ms)"

! t

GAMs

DW

CMTFO

GAMs Nonlinearly Scatter Density Fluctuations to Higher Frequency (Higher k-perp)

frequency (kHz)

frequency (Cs/a)

GYRO

DIII-D BES

Holland PoP’07

CMTFO

Key Observations

•  DWT - ZF/GAMs Dynamics Directly Observed •  ES (low-beta) & EM (finite beta) Intermittent

Structures at LCFS & in SOL •  These Can Drive Mean Parallel SOL Flows •  Mean ExB Shear Naturally Exists at the LCFS & Act

on Turbulence •  Turbulent Stresses Can Reinforce Parallel & Perp

Flows •  Mean Flows Can Also Affect Turbulent Stresses •  Neutral Recycling Can Damp ExB Shear Flows, ZF/

GAMs

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SOL Transport Occurs Via Intermittent Convective Bursts

Ref: S. Zweben et al APS ‘05 Invited Talk, May 2006 PoP

NSTX-PPPL

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Convective Transport via Blobs Dominate SOL Transport

Krasheninnikov, PLA’01

Enabled by Sheath Resistivity & Polarizing Mechanism

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Detailed  Structure  of  Blobs  

LAPD Carter et al, PoP06

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Blobs & Holes Born at LCFS

DIII-D Boedo PoP’03

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Detailed  Understanding  of  Origins  Emerging  

Fasoli-­‐EPS’10  &  TORPEX  references  therein

Propaga;on  Governed  by  Perp  v.  Parallel  currents

Garcia  et  al  NF07  ESEL  Sims  &  TCV  Expts

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Blobs  are  DriU-­‐Alfven  Vor;ces  w/  J||  and  Vor;city  

RFX ref: Spoliare, Vianello et al PRL’09

Radial motion of blobs => Vorticity Flux & Reynolds Stress)

Recent Work at ASDEX-UG Suggests Relationship to Type-I ELMs (http://arxiv.org/abs/0910.2362, Vianello, priv. Comm.)

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C-­‐Mod  L-­‐mode  Dimensionless  SOL  Gradients  Consistent  w/  EM-­‐DWT  Cri;cal  Gradient  Models  

C-MOD LaBombard PoP’08

What about effect of ExB Shear in H-mode?

CMTFO

Key Observations

•  DWT - ZF/GAMs Dynamics Directly Observed •  ES (low-beta) & EM (finite beta) Intermittent

Structures at LCFS & in SOL •  These Can Drive Mean Parallel SOL Flows •  Mean ExB Shear Naturally Exists at the LCFS & Act

on Turbulence •  Turbulent Stresses Can Reinforce Parallel & Perp

Flows •  Mean Flows Can Also Affect Turbulent Stresses •  Neutral Recycling Can Damp ExB Shear Flows, ZF/

GAMs

CMTFO

Turbulent  Flux  Lost  on  LFS  in  TORE-­‐SUPRA  L-­‐mode    

Fedorczak, PSI’10 submitted.

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SOL Transport Can Sustain “Mean” Parallel Flows

•  Perpendicular Transport Timescales Comparable to Parallel Flow Timescales:

•  Has Been Argued to Drive Mean Flow from LFS to HFS (Order ~ CS) �

τ⊥ ~λ⊥SOL

V⊥SOL ~100µ sec

τ || ~qRCS

~100µ sec

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C-­‐Mod  L-­‐mode  Core  Rota;on  Follows  HFS  SOL  Flows  

•  HFS SOL Flows Consistent w/ Ballooning-driven || flow picture

•  Core Toroidal Rotation Seems to Follow HFS SOL

•  LFS SOL always co-current

C-Mod LaBombard, PoP’08

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SOL Transport Can Sustain “Mean” Parallel Flows

•  Perpendicular Transport Timescales Comparable to Parallel Flow Timescales:

•  Has Been Argued to Drive Mean Flow from LFS to HFS (Order ~ CS)

•  BUT…Intermittent Ballooning Transport Should Also Cause Finite

�

τ⊥ ~λ⊥SOL

V⊥SOL ~100µ sec

τ || ~qRCS

~100µ sec

�

˜ v r˜ v ||

CMTFO

Key Observations

•  DWT - ZF/GAMs Dynamics Directly Observed •  ES (low-beta) & EM (finite beta) Intermittent

Structures at LCFS & in SOL •  These Can Drive Mean Parallel SOL Flows •  Mean ExB Shear Naturally Exists at the LCFS & Acts

on Turbulence •  Turbulent Stresses Can Reinforce Parallel & Perp

Flows •  Mean Flows Can Also Affect Turbulent Stresses •  Neutral Recycling Can Damp ExB Shear Flows, ZF/

GAMs

CMTFO

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 Erad at L-H Transition

Groebner PRL 1990, Doyle Phys. Fluids-B 1991

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Barrier Caused by Reduction of Turbulent Edge Transport

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Key Players and Interactions at LCFS/SOL

•  Large Amplitude Convective Blobs & Holes

• Naturally Occuring Shear Layer •  Turbulent-driven ZF/GAMs just inside LCFS

•  THESE THREE PLAYERS INTERACT AND CAUSE COMPLEX DYNAMICS

•  RESULTS HAVE PROFOUND IMPACTS ON MACHINE PERFORMANCE

• ESSENTIAL TO UNDERSTAND THESE INTERACTIONS

CMTFO

Key Observations

•  DWT - ZF/GAMs Dynamics Directly Observed •  ES (low-beta) & EM (finite beta) Intermittent

Structures at LCFS & in SOL •  These Can Drive Mean Parallel SOL Flows •  Mean ExB Shear Naturally Exists at the LCFS & Acts

on Turbulence •  Turbulent Stresses Can Reinforce Parallel & Perp

Flows •  Mean Flows Can Also Affect Turbulent Stresses •  Neutral Recycling Can Damp ExB Shear Flows, ZF/

GAMs

CMTFO

Hidalgo, ICPP 2010

CMTFO

Hidalgo, ICPP 2010

CMTFO

Hidalgo, ICPP 2010

CMTFO

Blobs  Carry  Momentum  &  Impact  Momentum  Balance  

RFX Vianello, PRL’05, PPCF’06

Steady-state Momentum Balance

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Image of Radially Sheared m=0 Zonal Flow

CMTFO

Flow Profile Consistent with Turbulent Momentum Balance

Tynan et al, April 2006 PPCF, , Holland et al, PRL 2006

CMTFO

Blobs  Carry  Toroidal  Momentum  &  Impact  Momentum  Balance  

Conditionally Averaged Blob Density, Toroidal Velocity Perturbation

TORPEX REF: Fasoli EPS’10

Blob Momentum Transport Can Impact Global Plasma Flow in TORPEX

CMTFO

Key Observations

•  DWT - ZF/GAMs Dynamics Directly Observed •  ES (low-beta) & EM (finite beta) Intermittent

Structures at LCFS & in SOL •  These Can Drive Mean Parallel SOL Flows •  Mean ExB Shear Naturally Exists at the LCFS & Acts

on Turbulence •  Turbulent Stresses Can Reinforce Parallel & Perp

Flows •  Mean Flows Can Also Affect Turbulent Stresses •  Neutral Recycling Can Damp ExB Shear Flows, ZF/

GAMs

CMTFO

External  (“Mean”)  Flow  Enhances  Long  Range  ZF  in  

TJ-­‐II  Estrada  PRL  2009

CMTFO

Bias-­‐driven  Mean  Flow  Enhances  ZF/GAM  Correla;on  

TEXTOR Xu PoP’09

CMTFO

Biasing Enhanced Long Range Potential Correlation

TJ-K Manz PoP’09

NO BIAS WITH BIAS

CMTFO

Biasing Can Reduce Turbulence Amp but INCREASE Stress…

TJ-II Alonso, EPL’09, Hidalgo ICPP’10

Bias Increases <Vr V||> Even When Reducing Turb Amplitude Caused by increase in Vr – V||

Cross-correlation

CMTFO

Externally  Driven  ExB  Shear  Stretches  and  Tilts  Blobs  

Carter & Maggs, PoP2009

CMTFO

Key Observations

•  DWT - ZF/GAMs Dynamics Directly Observed •  ES (low-beta) & EM (finite beta) Intermittent

Structures at LCFS & in SOL •  These Can Drive Mean Parallel SOL Flows •  Mean ExB Shear Naturally Exists at the LCFS & Acts

on Turbulence •  Turbulent Stresses Can Reinforce Parallel & Perp

Flows •  Mean Flows Can Also Affect Turbulent Stresses •  Neutral Recycling Can Damp ExB Shear Flows, ZF/

GAMs

CMTFO

Increased  SOL  Convec;ve  Flux  to  Wall  as  n/nG=>1  

Garcia NF’07

SOL Density Profiles Wall Flux v. nLCFS

Vconv~70m/sec

Similar to C-Mod (LaBombard IAEA’00), DIII-D (Whyte, Rudakov)

CMTFO

GAMs  Disappear  as  Approach  Density  Limit  

TEXTOR XU, IAEA’10

CMTFO

Need to Include Mean ExB Shear Into DWT-ZF/GAM Model"

Drift waveturbulence

Zonal flows

Shearing

Collisional flow damping

SUPPRESSNonlinear flow damping

energyreturn

DRIVE

<vx vy>~~

!T, !n...

<vx p>~~Transport

Ref: Itoh PoP06

Mean Shear Flows

?

CMTFO

Such  a  Model  is  KEY  to  Origin  of  both    L-­‐H  Transi;on  &  Intrinsic  Rota;on

•  NSTX  (Zweben)  Reports  Onset  of  Limit  Cycle-­‐like  Phenomena  w/  GAM  Amplitude,  Turbulence  Approaching  L-­‐H  Transi;on  

•  Similar  Observa;ons  from  ASDEX  UG  (Conway)  •  HL-­‐2A  Sees  Significant  Increase  in  GAM  and  ZF  Amplitudes  as  Approach  L-­‐H  Power  Threshold  

•  DIII-­‐D  Sees  Rapid  (50msec)  Buildup  of  Toroidal  Rota;on  Layer  at/near  LCFS,  Followed  by  Core  Spinup  

CMTFO

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

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

CMTFO

Turbulence/GAMs/Mean  ExB  Limit  Cycle  Approaching  L-­‐H  

•  Limit Cycle in Turbulence & GAM Amp Observed –  High Turb/High

GAM Amp/Strong Er well

–  Low Turb/Low GAM Amp/Weaker Er well

�

Er × B( )GAM ≈ Er × B( )Mean

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

CMTFO

GAM/ZF  Amplitude  Increase  Strongly  as  Paux  is  Increased  

HL-2A Zhao et al, submitted (private comm.)

Does GAM or ZF Shearing Rate Become Significant?

CMTFO

ZF  and  GAMs  Regulate  Turbulence  in  L-­‐mode  

HL-2A Zhao et al, submitted (private comm.)

Left: ZF & GAM Coherency & Phase w/r/t HF Turbulence Right: ZF/GAM Coherency & Phase w/r/t 50kHz-wide band

CMTFO

Other Interesting Topics w/o Enough Time to Discuss or Review

•  Recovery of Fluctuations in Pedestal (Z. Yan/UW-Madison, BES DIII-D)

•  Turbulence Increase in RMP as Possible Origin of Density Pumpout (DIII-D, MAST)

•  Link b/w Perpendicular Blob Dynamics and Divertor Heat Loads (NSTX/DIII-D/C-Mod, Mainji-ORNL)

•  Studies of Intrinsic Rotation in Lab Plasma Device (UCSD)

•  Evidence for Edge-Core Coupling: Rapid core turbulence suppression; core GK simulations systematically underestimate out region transport (McKee, Holland)

CMTFO

Thank you for your attention