Edge and Internal Transport Barrier Formations in CHS

S. Okamura, T. Minami, T. Akiyama, T. Oishi1, A. Fujisawa, K. Ida, H. Iguchi, M. Isobe, S. Kado2, K. Nagaoka, K. Nakamura, S. Nishimura, K. Matsuoka, H. Matsushita, H. Nakano, M. Nishiura, S. Ohshima, A. Shimizu, C. Suzuki,

C. Takahashi, K. Toi, Y. Yoshimura and M. Yoshinuma

National Institute for Fusion Science, Oroshi 322-6, Toki 509-5292, Japan1) Graduate School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan

2) High Temperature Plasma Center, The University of Tokyo, Tokyo 113-8656, Japan

Rapported paper

Identification of Zonal Flows in CHS and JIPPT-IIU

Transport Studies in CHS (Compact Helical System)

Confinement ImprovementTransport Barrier Formations

Turbulence andPlasma Flow Structure

(Er) Measurement

Internal TransportBarrier (ITB)

FEC2002(Lyon)Density ThresholdNe < 0.4 x 1019 m-3

Zonal FlowMeasurement

by HIBP

ECH Plasmas

without beam driven instabilities

Edge TransportBarrier (ETB)

NBI Plasmas

Transport Barriers for higher-density Plasmas

First Talk Second Talk

Edge Transport Barriers (ETB) in CHS Experiment

CHS(Compact Helical System)R = 1 m, Bt < 2 T, Ap = 5

-25

-20

-15

-10

-5

0

5

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1

-dV

/d

(%

) Iota

[1/q

(r)]

Normalized Radius (r/a)

Rotational Transform

MagneticWell

MagneticHill

1992 IAEA conference at Würzburg

K. Toi, S. Okamura, H. Iguchi, et al." Formation of H-mode like transport barrier in the CHS heliotron/torsatron "

Ip ~ 30 - 40 kA for Bt ~ 1.2 - 1.4 T

Iota(0) : 0.25 0.8Iota(a) : 0.9 1.1

Present Experiment

2. No ohmic current drive (< 10 kA bootstrap and beam driven current)

with Ohmic current control

1. Use standard configuration Rax = 92.1 cm

3. Two NBIs both in co-injection

H-mode Transition in NBI Heated Hydrogen Discharge

Magnetic Configuration : Rax= 92.1 cm, = 1.22 Bt= 0.95 T, PNBI= 0.6 MW

0

1

2

Wd

ia(k

J)

Ne 0.63a

0

1

2

3

4

Ne

(x1

019m

-3)

0

200

400

600

0 0.05 0.1 0.15 0.2

Radiation(kW)

P.r

ad

(kW

)

Time(sec)

NBI.#1

NBI.#2

ECH

Transition to ETB

Back Transition

H

Energy

Edge Density

Radiation

0

0.1

0.2

0.3

0.4

0.5

0.6

-1 -0.5 0 0.5 1

75 msec80 msec

Te (

keV

)

(r/a)

0

0.5

1

1.5

2

2.5

3

3.5

4

-1 -0.5 0 0.5 1

75 msec80 msec

Ne

(1

019 m

-3)

(r/a)

YAG Thomson Measurement

Den

sity

Pro

file

Tem

pera

ture

Pro

file

Edge Transport Barrier

Beam Emission Spectroscopy (BES) for Local Density Measurement

ECHNBI.#1NBI.#2

(a)

(b)

0

100

200

300

R=1.053 m(c)

BE

S E

mis

sion

0

30

60

90

0 0.05 0.1 0.15 0.2

R=1.075 m

Time(sec)

(e)

BE

S E

mis

sion

0

50

100

150

200

R=1.064 m(d)

BE

S E

mis

sion

R=1.053 m

BE

S E

mis

sio

n

R=1.064 m

0.06 0.065 0.07 0.075 0.08

R=1.075 m

Time(sec)

LCMS

Pre-phase of transition

H H

Expanded View

Heating Power Dependence of Transition

Magnetic Configuration : Rax= 92.1 cm, = 1.11 Bt= 0.95 T

ECHNBI#1

#104571

NBI#2Puff

Time delay from NBI start to transition

0.06 0.065 0.07 0.075 0.08 0.085 0.09

<nl>.centerH.alpha<nl>.edge

Time (sec)

DT2DT1

DT3

0

5

10

15

20

25

30

35

40

0.4 0.5 0.6 0.7 0.8 0.9

DT3DT2DT1

Del

ay T

ime

(mse

c)Heating Power (MW)

Power threshold for Ne = 2 x 1019 m-3

Twice larger than tokamak scaling

ETB Formation with Improved Electron Confinement

When the density profile shape is hollow during the transition phase, improved electron confine- ment is simultaneously obtained with ETB for NBI plasma without ECH

0

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800

Ne-av Radiation(kW)

(x1

019m

-3)

0

1

2

0 0.05 0.1 0.15 0.2

Wd

ia(k

J)

Time(sec)

NBI.#1

NBI.#2ECH

YAG Thomson Measurement

Edge Transport Barrier

0

1

2

3

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5

6

7

-1 -0.5 0 0.5 1

65 msec70 msec

Ne

(1

019 m

-3)

(r/a)

0

0.2

0.4

0.6

0.8

1

-1 -0.5 0 0.5 1

65 msec70 msec

Te (

keV

)

(r/a)

Internal Transport Barrier

Den

sity

Pro

file

Tem

pera

ture

Pro

file

SUMMARY

1. Formation of transport barrier at plasma edge for particle flow was observed in CHS and dynamics of edge density profile was studied.

2. Heating power threshold exists for the transition. It is roughly two times larger than tokamak scaling.

3. When the density profile is hollow shape during the transition, the improvement of electron heat transport was simultaneously observed (without ECH) for middle density plasma (Ne ~ 3 x 1019 m-3) which is above density threshold of previous ITB experiments in CHS.

Identification of Zonal Flows in CHS and JIPPT-IIU

A. Fujisawa, K. Itoh, H. Iguchi, K. Matsuoka, S. Okamura, A. Shimizu, T. Minami, Y. Yoshimura, K. Nagaoka, C. Takahashi, M. Kojima, H. Nakano, S. Ohshima, S. Nishimura, M. Isobe, C. Suzuki, T Akiyama, K. Ida, S.-I. Itoh1 and P. H. Diamond2

Y. Hamada, A. Nishizawa, T. Ido, T. Watari, K. Toi, Y. Kawasumi and JIPPT-IIU group

National Institute for Fusion Science1Kyushu University, RIAM2University of California, San Diego

Zonal Flows

The zonal flow appears in E-field fluctuation in toroidal plasma

Is that really present in toroidal plasma?

ITER

Poloidal Crosssection

m=n=0, kr=finite

ExB flows

HIBP is a strong candidate for identification of zonal flows

zonal flows: regulating turbulence and transport

Two branches

2) Geodesic acoustic mode Oscillatory (f~ Cs/R) -DIII-D(BES) -ASDEX-U(Reflectometor) -H1-heliac (probes) -JFT-2M (HIBP)

1) Zonal flow nearly zero frequency

This finding!

HIBP in JIPPT-IIU Tokamak

0

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0 10 20

Am

plit

ud

e (

V)

r (cm)

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0 10 20

f (k

Hz)

r (cm)

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90 100 110 120

Z (

cm)

R(cm)

450 kV

250 keV

300 keV 2

6

94 96

450 kV

0

100

200

15 30 45 60 75

P (

V2/k

Hz)

f (kHz)

0.2

Potential fluctuation M=0 symmetry

Amplitude vs. radius Frequency vs. radius

Observation points

Multi-channel measurements up to 6

Coherent oscillation was found to show GAM characteristics

-1

0

1

-20 -10 0 10 20(s)

1&1

C(0)=0.80 =53.7s f=46 kHz

-1

0

1 1&4

C(0)=0.79 =58.6s f=46 kHz

Dual HIBPs in CHS

E rr out cen

Electric field measurement ECR-heated plasma

ne=5x1012cm-3 Te=1.5 keV Ti=0.1 keV

R=1m, a=0.2m

HIBP#1 observation points

HIBP#2 observation points

ExB flow

Er

ctr

in

out

Poloidal Crosssection 2

Er

Poloidal Crosssection 1

ctr

in

out

ExB flow

HIBP System

90 degree apart

R=1m, a=0.2m

Spectrum of electric field fluctuation

r ~12 cm (r/a~2/3)

Low frequency fluctuation (f<1kHz) shows a long-range correlation

Zonal flow is identified

0.01

0.1

1

0

0.5

1

0.1 1 10 100

PE(V

2 /kH

z)

Co

he

ren

ce

f (kHz)

noise level

GAM

Zonal flows

Dynamics and Structure of Zonal Flows

A numerical filter is used to remove high frequency (f>1 kHz)

-1

0

1

55 60 65 70 75

E

(V

)

t (ms)

E1

in

E2

in

r1=12cm r

1=12.5cm

on slightly different magnetic flux surfaces

-1

0

1

55 60 65 70 75

E

(V

)

t (ms)

E1

in

E2

in

r1=r

2=12cm

~1 Vpp

on a magnetic flux surface

Ccrs(r1,r2) E1(r1)E2(r2) / E12(r1) E2

2(r2)

Radial wavelength ~1.5 cm

Dynamics and radial structure of zonal flows are measured.

-1

-0.5

0

0.5

1

10 11 12 13 14

C (

r 1,r2)

r2 (cm)

r1=12cm

Confinement & Zonal Flow

Zonal flow amplitude is reduced after back-transition

Bifurcated states in CHS Time evolution of turbulence &zonal flow

0 0.5 10

0.5

no ITB

ITB

(k

V)

HIBP#1

HIBP#2

Potential HIBP#1

Density fluctuation HIBP#2

Zonal flow HIBP#2

with ITB without ITB

(K

V)

n/

n

(V)Dual HIBPs caught the exact mom

ent of spontaneous transition in a discharge.

0.3

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0.1

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5

-570

60

50

80

90t

(ms)

Summary

1. Heavy ion beam probe successfully measured the local electric field fluctuation spectrum.

4. The amplitude of the zonal flows is found to be reduced in the barrier location after the transport barrier decayed.

3. The amplitude of zonal flow is about 1 V. The radial wavelength is ~1.5 cm.

1. Coherent oscillation with GAM characteristics was found in the HIBP measurements on JIPPT-IIU tokamak.

JIPPT-IIU

CHS

2. Dual HIBPs confirm the presence of zonal flows (f<~1kHz) by showing a long-distance correlation with toroidal symmetry in electric field fluctuation

GAM in CHS

0.04

0.08 Er

Po

we

r (V

2 /kH

z)

0

0.5

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12 14 16 18 20 22

Coh

eren

ce

f (kHz)

0.01

0.1

1

0

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0.1 1 10 100

Pow

er (

V2 /k

Hz)

Coh

eren

ce

f (kHz)

Noise level for power

P~f-0.6

0.01

0.1

1

10

100

0

0.5

1

0.1 1 10 100

Pow

er (

V2 /k

Hz)

Coh

eren

cef (kHz)

P~f-1.9

Noise level

GAM in potential & electric field

Lithium Beam Probe Measurement of Edge Density Profile

ECHNBI.#1NBI.#2

0 0.05 0.1 0.15 0.2

H-a

lpha(A

.U.)

Time(sec)

#106281

T1 T2 T3 T5 T7T4 T6 T8

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4

6

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0.7 0.8 0.9 1 1.1 1.2

T1T2T3T4T5T6T7T8

De

nsi

ty(A

.U.)

Position (r/a) [for 0.8% beta]

LCMS for 1.0% beta

Confinement Improvement in Comparison with Scaling

0

0.5

1

1.5

2

2.5

3

0 1 2 3 4 5 6

with ETBISS04 ScalingNo ETBN

orm

aliz

ed

Wp

/(P0.3

9 ) (A

.U.)

Average Density (1019m-3)

41.03/2

85.055.061.064.033.2304 148.0 BnPRa eabsvISS

E

New International Stellarator Scaling H. Yamada, et al. :This conference EX/1-5

for CHS/ATF/Heliotron-E renormalization factor = 0.42

Maximum energy of each discharge is plotted as a function of average density

Confinement improvement of about 40% is given by ETB formation