Experimental Progress on Zonal Flow Physics in Toroidal Plasmas

A. Fujisawa, T. Ido, A. Shimizu, S. Okamura, K. Matsuoka, Y. Hamada, 1K. Hoshino, 2Y. Nagashima, 1K. Shinohara, H. Nakano, S. Ohshima, 1Y. Miura, K. Itoh, S. –I. ItohNIFS, 1JAEA, 2RIAM, Japan

M. Shats, H. Xia, ANU, Australia

J. Q. Dong, L. W. Yan, K. J. Zhao, SWIP, China

G. D. Conway, *U. Stroth, Max-Planck institute,*Universität Stuttgart, Germany

A. Melnikov, L.G. Eliseev, S.E. Lysenko and S.V. Perfilov, Kurchatov Institute, Russia

C. Hidalgo, CIEMAT, Spain

G. R. Tynan, *G. R. Mckee, C. Holland, *R. J. Fonck, *D. K. Gupta, P. H. Diamond, UCSD, *Univ. Wisconsin U.S.A.

What is a ZONAL FLOW

ITER

Poloidal Crosssection

m=n=0, kr=finite

ExB flows

Zonal flows are ubiquitous.

2. Turbulence driven

1. No linear instability

3. No radial transport

Two braches of ZFs in a toroidal plasma

i) stationary zonal flows (sZF)

ii) geodesic acoustic modes (GAMs)

Is that really present in toroidal plasmas?

P. H. Diamond et al. PPCF 47 R35 (2005)

near-zero frequency ~0 kHz

an oscillatory branch ~ 10-50 kHz

Zonal flow in atmosphere in Jupiter

Why are ZFs Important for Fusion?

Nonlinear interaction between zonal flows and turbulence controls transport.

Because the zonal flows are deeply associated with anomalous transport.

A question: the paradigm shift is experimentally supported?

Drift waves

Drift waves+

Zonal flows

the new paradigm

gradients

damping

turbulence Zonal flows

€

v∇v

trapping

no transport

transport

shearing sZF>GAMPlasma Transport

Zonal Flow Experiments

- electric field or flow measurements in high temporal and spatial resolution

A challenge to experimentalists

i) zonal structure

symmetry (m=n=0)a finite radial wavelength

ii) nonlinear coupling with turbulence

Discoveries

iii) effects on transport

HL-2A (probes)

JIPPT-IIU (HIBP)

T-10 (HIBP)

ASDEX-U (reflectometry)

JFT-2M(HIBP&probes)

DIIID (BES)

CLD (probes)

CASTOR (probes)

TJ-II(probes)

TEXT-U (HIBP)

H1 (probes)

CSDX (probes)

HT-7 (probes)

CHS(HIBP)

LMD (probes)

TJ-K(probes)

Devices

More than a dozen papers have been published as a PPCF cluster (2006).

Existence of Stationary Zonal Flow

Proceeded by a pioneer work in HT-7, CHS has confirmed the existence of sZF

New techniques for ZF detection are developed in CATOR and CLD.

G. S. Xu et al., PRL 91 125001 (2003).

-1

0

1

55 60 65 70 75 ( )t ms

E1in

E2in

r1=12cm r

1=12.5cm

time (ms)

-1

0

1

55 60 65 70 75 ( )t ms

E1in

E2in

r1=r

2=12cm

time (ms)

CHSf~0.5 kHz

0 50f (kHz)

Pow

er (

flow

)

m=0DIII-D

1 100f (kHz)

Pow

er (

flow

)

ASDEX-U sZF

This IAEA EX2-3: G. Mckee et al.

G. D. Conway, 31st EPS conf. London

Showing Symmetry

A. Fujisawa et al. PRL 93 165002 (2004).

Showing a finite radial wavelength

HIBP#1observation points

HIBP#2observation points

ExB flowErφctrφinφoutPoloidal Crosssection 2ErPoloidal Crosssection 1φctrφinφoutExB flow

Zonal structure is found!

Pattern of Stationary Zonal Flow

This is the discovery of stationary zonal flow.

€

Ccrs(r1,r2,τ ) = E1(r1, t)E2(r2, t + τ ) / E12(r1, t) E2

2(r2, t + τ )

Using the cross-correlation functions between two electric fields at different radii,

10001 f (kHz)(Log)

GAMs in Spectra

Coherent modes have been detected in many toroidal devices

The HL-2A tokamak confirms the complete symmetry (n=m=0) of GAM

After H1-heliac reported the existence of GAM,

This IAEA EX/P4-35 L.W. Yan et al.

0 100

400

60f (kHz)0

JFT2M

T10

TEXT-U

f (kHz)

f (kHz)

Potential(HIBP)

400 f (kHz)

flow(BES) flow(reflectometry)

DIII-D ASDEX-U

potential (probe)

M. G. Shats et al., PRL 88 45001 (2002)

1001 f (kHz)

HL-2A

(Log)

0

25

f GAM

(kH

Z)

cs/R

=1.12

=1.73

=1.40=1.27

=1.62

GAM Frequency Dependence

This IAEA EX2-1 G. Conway et al.

ASDEX

DIII-D

The frequency of the coherent modes satisfies

the expected dependence.

G. R. McKee et al., PPCF 48 S123 (2006).

0

5

10

15

20

25

0 5 10 15 20 25

CHS(ECH)

ASDEX(L-mode)

ASDEX(ohmic)

JFT2M(ohmic)

JFT2M(NBI)

DIII-D(NBI)

T10

f=cs/R

cs/2π ( )R kHz

fGAM

=cs/2πR

fGAM (kHz)- theory

€

fGAM ∝ cs /R

The studies of GAM have an impact on

understanding of plasma turbulence

DIII-D

4.0 7.0q95G

AM

am

plitu

de

Landau damping?

-100

0

100

1200 f1 (kHz)f 2

(kH

z)

strong coupling

f1+f2=f3 ~±10kHz

JFT2M

This IAEA EX2-2 K. Hoshino et al.

How to Prove Nonlinear Couplings

f1+f2= f3

(bicoherence=0, if f1+f2≠0)

Bicoherence analysis can quantify the strength of three wave coupling.

- Direct measurement of energy transfer term from turbulence to flow is performed in TJ-II, showing

importance of parallel component .

€

˜ v || ˜ v r

(k1+k2= k3 )

This IAEA EX/P7-2 C. Hidalgo et al.

Reynolds stress to drive mean flow

-Direct evaluation of perpendicular term has been widely performed (CSDX, HT-6M, LMD, TJ-K, etc.)

€

˜ v ⊥˜ v r

Other techniques (energy transfer, autocorrelation, etc. ) are developed M. Shats et al., PPCF 48 S17 (2006).

G. R. Tynan et al.PPCF 48 S51 (2006).

Energy Transfer between ZF and Turbulence

Turbulence power changes intermittently with ‘zonal flow’

Anti-phase behavior suggests direct energy transfer between

‘zonal flow’ and turbulence

turbulence‘sZF’

GAM GAM

turbulence

norm

aliz

ed p

ower

Time (ms)40 70

‘sZF’

CHS

A. Fujisawa et al. PPCF 48 A365 (2006).

10-8

10-7

10-6

10-5

0

0.5

1

1 10 100f (kHz)

power

coherence

GAM turb.sZF

Effects on Transports

ZF Effects on Transport

HIBP has an advantage in simultaneous measurements of ZF and particle flux

CHS

T. Ido et al., PPCF 48 S41 (2006)Similar result is obtained for GAMs in JFT-2M.

Stationary zonal flow

particle flux density

maximum

minimum

potential fluctuation5ms

40 70Time (ms) f (kHz)30 80

pow

er

ZF

f (

kHz)

020

0

0at maxium

at minimum

Conditional averages0.5

A. Fujisawa et al., PPCF 48 S205 (2006).

Particle flux is really modulated with stationary zonal flow.

Better Confinement in Enhanced ZF

A larger fraction of zonal flows contributes to confinement improvement inside

the barrier! Importance of zonal flows on confinement is demonstrated.

CHS Why is the confinement improved in shearless regime inside the barrier?

0 1 2 3P

ZF(V

2)

L mode

H mode

Po

wer

( E

/T

)∇

~

10-3

No ITB

ITB

At a radius without mean Er-shear

inside the barrier

no ITB

ITB

radius0 1

Pot

entia

l (or

Tem

pera

ture

)

confinement is improvedwithout shear

Common ITB in helical plasmas

Clear difference in energy partition

What Experiments Achieved

The experiments on zonal flows have made a large progress.

The obtained knowledge are still fragmental, but support the fundamental expectations of the theories.

S-ZF

GAM

structure nonlinear coupling effects on transport

confirmed

Turbulence modulation is observed.

Turbulence modulation is observed

in a casen=m=0

n=0

confirmed

confirmed (bicoherence)

m=0 confirmed

kr=finite proven

m=0 confirmed confirmed(temporal correlation)

kr=finite

fGAM~cs/R

Eigenmode property

Importance of flow energy partition is demonstrated

Summary

The world-wide experiments on zonal flows show,

- The experiments support the paradigm shift!

Drift waves

Drift waves+

Zonal flows

- The prospect of ITER is enhanced.ITER will be more analogous to the Sun than the Jupiter.

ASDEX-U, CASTOR, CHS, CLD, CSDX , DIII-D, H1, HL-2A, HT-6M, HT-7, JFT-2M, JIPPT-IIU,LMD, T-10, TEXT-U, TJ-II, TJ-K and so on

- Zonal flows really do exist in toroidal plasmas.

Common physics

Zonal flow in CHS