experimental progress on zonal flow physics in toroidal plasmas a. fujisawa, t. ido, a. shimizu, s....
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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
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