Configuration Control Studies of Heliotron JF. Sano, et al.

Kyoto University

Progress of Confinement Physics Study in Compact Helical System

S. Okamura, et al.National Institute for Fusion Science

EX/5-5Ra

EX/5-5Rb

21st IAEA Fusion Energy Conference, 16-21 October 2006, Chengdu, China

Heliotron J CHS

Heliotron J (2000 - )- helical-axis heliotron L=1/M=4- R=1.2 m, B < 1.5 T- ap=0. 17 m- Ap=7- a/2~ 0.56 low shear- ECH/NBI/ICRF systems

CHS (1988 - 2006)- LHD-type heliotron L=2/M=8- R=1 m, B < 2 T - ap=0.2 m- Ap=5 　　 low aspect ratio- a/2~ 0.8-1.2 high shear at edge- ECH/NBI/ICRF systems

Heliotron J : (a)/ and b Control Studies

CHS : Transport Barrier Physics Studies

Opportunities and challenges to experimentallystudy the key issues of helical system optimization

Bilateral collaboration Program of NIFS

Configuration Control Studies of Heliotron JOptimization study of a helical-axis heliotron

FEC2006

21st IAEA Fusion Energy Conference, 16-21 October 2006, Chengdu, China

F. Sano1, T. Mizuuchi1, K. Kondo2, K. Nagasaki1, H.Okada1, S. Kobayashi1, K. Hanatani1,Y. Nakamura2, Y.Torii1, S. Yamamoto4, M.Yokoyama5, Y. Suzuki5, M. Kaneko2, H. Arimoto2, G. Motojima2, S. Fujikawa2, H. Kitagawa2, H. Nakamura2, T. Tsuji2, M. Uno2, H. Yabutani2, S.Watanabe2, S. Matsuoka2, M. Nosaku2, N. Watanabe2, N. Nishino6, Z. Feng 7, Y.Ijiri1, T.Senju1, K.Yaguchi1, K.Sakamoto1, K.Tohshi1, M.Shibano1

1Institute of Advanced Energy, Kyoto University, Uji, Japan; 2Graduate School of Energy Science, Kyoto University, Kyoto, Japan; 3Graduate School of Engineering, Kyoto University, Kyoto, Japan;4Graduate School of Engineering, Osaka University, Suita, Japan; 5National Institute for Fusion Science, Toki, Japan; 6Graduate School of Engineering, Hiroshima University, Hiroshima, Japan; 7Southwestern Institute of Physics, Chengdu, China;

To extend the understanding of neoclassical transport of 3-D plasmas and the related role of field ripples such as bumpiness in confinement improvement for the quasi-omnigeneous approach of the optimization of a helical-axis heliotron.

Objective

1. Introduction2. Objective3. Experimental Setup4. Results and Discussion about the Bumpiness Control Studies . Plasma Current Control . Fast Ion Confinement . Bulk Plasma Confinement 5. Summary

Outline

High-quality H-mode appears to be linked with access to the specific vacuum(a)/ values.

Bootstrap current control

For the fixed (a)/=0.56, the bumpiness only was varied by using the independent control of each toroidal coil current (TA or TB) under almost the same h and t conditions.

Bumpiness control studies under the fixed vacuum (a)/=0.56: (1) Low-b, (2) Medium-b, and (3) High-b configurations.

(a)/=0.56

b

t

h

Poster EX/P6-14 “Control of Non-Inductive Current in Heliotron J”, K.Nagasaki, G.Motojima, et al.

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.5 1.0 1.5 2.0

B04

/B00

=0.15

B04

/B00

=0.01

B04

/B00

=0.06

Ip [k

A]

ne [1019 m-3]

=0.499

Bumpiness plays an important and effective role in the control of the bootstrap current and electron cyclotron current drive (ECCD) in Heliotron J.

ECCD control

High-b

Medium-b

Low-b

Configuration Set-up

0

2

4

6

8

0 0.1 0.2B04/B

00

18keV

24keV

*(Eb->18keV)

*(Eb->24keV)1/

e de

cay

time

(ms)

Bumpiness dependence of 1/e decay time

For NBI heating, the 1/e decay time of CX-flux after NBI turned off suggests that the higher b con

figuration is more favorable for the fast ion confinement due to the reduced B drift. For ICRF heating, the high-energy ion tail temperature increases with an increase in b .

NBI

ICRF

Poster EX/P6-1“Dependence of the Confinement of Fast Ions Generated by ICRF Heating on the Field Configuration in Heliotron J”, H.Okada, et al.

0 2 4 6 8 10

E (keV)

1E+016

1E+017

1E+018

1E+019

1E+020

1E+021

1E+022

f H (

E)

NPA=3deg

STD (B04/B00 = 0.06)19MHz

(0.01)19MHz

(0.15)23.2MHz

0.87 keV

1.04 keV

0.47 keV

0

0.1

0.2

0.3

0.4

0.01 0.1 1time (ms)

0.01

B04

B00

=0.150.06

Low-b

High-b

Medium-b

High-b

Medium-b

Low-b

Loss rate from orbit calculation

High-b

Medium-bLow-b

ne=0.4x1019m-3

tu

rbu./I

s

Distance from LCFS (mm)-10 0 10 20 30 40

10-3

10-2

10-1

I s (

A)

ECH-only Low Density

b = 0.01b = 0.06b = 0.15

10-2

10-1

Vs (

V)

0

100

200

Vf (

V)

-50

0

50

Te

(eV

)

0

50

100

Low-b

Medium-b

High-b

LCFS

As for bulk plasma confinement, the experimental bumpiness dependence of the volume normalized plasma energy of the 70-GHz, 0.3-MW ECH as a function of density suggests that the medium-b plasmas provide more favorable thermal confinement properties.

Depending on the density evolution, ECH plasma spontaneously develops into H-mode at densities higher than the threshold density, followed by radiation collapse in a time scale of E

exp.

Medium-b

Edge/SOL Characteristicsin the low-density case

FEC2006

For high-b, a weak (or slow) L-H transition only was observed at this ECH power level. This indicates that the configuration modified with the bumpiness affects the threshold nature of H-mode in Heliotron J. For low-b, the dithering transitions showed only a modest improvement of Wp as a result of density rise.

High- b Low- b

Calculated neoclassical poloidal viscous damping rate coefficient Cp as a function of radius r (m) for high-b, medium-b and low-b configurations.

The difference in Cp between the three configurations considered here are almost negligible, much more work is necessary before comparison with experiment.

Eexp =Wp/(absPECH - dWp/dt)

abs= abs1+ ref(1- abs

1)under the assumption of ref=0.3.

The reduction of the neoclassical diffusion coefficient depends on the appropriate choice of b.

The results 1) from the DCOM code showed that the medium-b configuration provides a greater degree of neoclassical optimization in the 1/ regime.

1) The results (eff) were recently revised and a factor 2 larger than before.

The reduction in eff suggests a favorable effect on the confinement of ECH plasma in the L-mode and the transient phase of the H-mode ( including dWp/dt effects) .

However, due to the large data scatter and inherent error bars, further studies are necessary to understand the more statistical and physical trends of anomalous confinement of ECH plasmas.

Summary

1. Bumpiness control experiments have been carried out with special reference to the omnigeneous (isodynamic) optimization of a helical-axis heliotron.

2. The bumpiness was found to effectively control the bootstrap current and the balance of the ECCD mechanisms (EX/P6-14).

3. The NBI and ICRF experiments suggest that the higher-b configuration provid

es better fast ion confinement (EX/P6-1).

4. The ECH experiments suggest that the lower ”effective helical ripple, eff” confi

guration of medium-b provides better global energy confinement in the L-mod

e and also in the transient phase of H-mode.5. Further studies are necessary to determine what effect (including the plasma ele

ctric field, the plasma flow and/or edge/SOL plasma behavior) makes up the observed difference between the bumpiness dependence or the ”effective helical ri

pple, eff” dependence. It should be noted here that the effective helical ripple re

presents the local neoclassical diffusivity in the 1/ regime and that as for fast ion confinement, the drift loss is essentially important.

Configuration Control Studies of Heliotron J

Confinement Physics Study in Compact Helical System

S. Okamura, T. Akiyama, A. Fujisawa, K. Ida, H. Iguchi, R. Ikeda, M. Isobe, Y. Jinguji, S. Kado 1, T. Kobuchi, K. Matsuo 2, K. Matsuoka, T. Minami, S. Mizuno, K. Nagaoka, K. Nakamura, H. Nakano, S. Nishimura, T. Oishi, S. Ohshima, A. Shimizu, C. Suzuki, C. Takahashi, M. Takeuchi, K. Toi, N. Tomita 3, S. Tsuji-Iio 3, Y. Yoshimura, M. Yoshinuma and CHS group

CHSCHS

1) High Temperature Plasma Center, The University of Tokyo, Chiba, Japan

2) Fukuoka Institute of Technology, Fukuoka, Japan

3) Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Tokyo, Japan

National Institute for Fusion Science, Toki, Japan

Progresses in ITB Physics

• Ion Confinement Improvement

• Turbulence Measurement with HIBP

Progresses in ETB Physics (H-mode)

• Edge Turbulence Measurement

• Edge Electric Field Measurement

• New H-mode with High Density

• Edge Harmonic Oscillation Study

Progresses in TAE & EPM Study

• Local Measurement of Energetic Particles

Poster EX/P8-1

Poster EX/P6-81/7

Ion Confinement Improvement for ITB Plasma

0

0.5

1

1.5

2

2.5

3

-1 -0.5 0 0.5 1

Te (

keV

)

(r/a)

0

0.1

0.2

0.3

0.4

0.5

0.6

-1 -0.5 0 0.5 1

Ti (

keV

)

(r/a)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-1 -0.5 0 0.5 1

Ne

(x1

019

m-3)

(r/a)

0

2

4

6

0 0.2 0.4 0.6 0.8 1

65 msec85 msec

Te (

keV

)

(r/a)

(a)

-5

0

5

10

15

0.4 0.5 0.6 0.7 0.8 0.9

58 msec66 msec70 msec88 msec

dT

i/dR

(ke

V/m

)

(r/a)

(b)

Ion Temperature Gradiant Measure

ment

1. Steep temperature gradiant (13 keV/m) for ions is measured using new TVCXS diagnostic

2. Locations of transport barriers are different for electrons and ions in ITB discharges

CERC Plasma with NBI

Electron Temperature

Ion Temperature

Electron Density

Foot points of temper-ature gradient (internal transport barrier) appear to be different

More precise information is required for transport barrier structure study

Electron Temperature Profile

Ion Temperature Gradient

dTi(R)insead of Ti(R)

dR

2/7

Measurement of Turbulent Flux by Heavy Ion Beam Probe

40 60 80 100

200

150

100

50

col

row

-0.0005 -0.0000 0.0005 0.0010test_txt_3_md

200

40 60 80 100Time(ms)

150

50

100f (k

Hz)

0

0

0.0004

0.0008

0.0012

0.15

0.2

0.25

0.3

40 50 60 70 80 90 100

flux

(a.u

.)

(k

V)

time (ms)

Flux at ~70kHz

transition

0

1

flux

(a.u

.)

r nE p

B kpnkksink /B

k

00.

10.

20.

30.

40.

5

0 0.2 0.4 0.6 0.8 1

(kV

)

Fluctuation

Dome (fine structure)

Hill

HIBP measured suppression of turbulent particle flux (in the frequency range of 70 kHz) when the Internal Transport Barrier (ITB) is formed.

Turbulent flux is estimated with measured fluctuations of density and potential

with ITB no ITBBack-transition

HIBP fluctuation measurement

3/7

0.50.40.30.20.10.0

0.6

0.4

0.2

0.0

0.200.150.100.050.00

0.120.100.080.060.040.020.00

16014012010080604020time [msec]

0.6

0.4

0.2

0.0

#117332

r/a=0.85

r/a=0.95

r/a=1.03

r/a=1.1

Ha

Measurement of Edge Fluctuations for H-mode Plasma

BES measures suppression of turbulence at plasma edge

Beam Emission Spectroscopy (BES) measures edge pedestal of H-mode

ECHNBI.#1NBI.#2

#124182(a)

0

1

2

3

4

Ne

(x1

019

m-3

)

(b)

0

1

2

Wd

ia(k

J) (c)

(d)

0 50 100 150

BE

S C

ha

nn

els

(A

.U.)

(e)r/a=0.76

r/a=0.85

r/a=0.95

r/a=1.03

r/a=1.10

Time (msec)

Large reduction of fluctuation at (r/a)=0.95

RMS value (0-100 kHz)

4/7

H-a

lpha

Measurement of Edge Electric Field using Carbon VI Doppler Shift

-10

-8

-6

-4

-2

0

2

4

1.16 1.17 1.18 1.19 1.2 1.21 1.22 1.23

70 msec90 msec110 msec130 msec

V(k

m/s

)

R(m)

(a)

0

50

100

150

1.16 1.17 1.18 1.19 1.2 1.21 1.22 1.23

70 msec90 msec110 msec130 msec

Ti(

eV

)

R(m)

(b)

Negative radial electric field of Er ~ 10 kV/m appeared with ETB formation

Electric field shear of ~ 2 MV/m2 is created just inside the last closed magnetic surface and sustained during H-mode

V(k

m/s

)

Ti (e

V)

Ele

ctro

n D

iam

agne

tic

Dire

ctio

n

Poloidal flow speed of C6+ Edge ion temperature

(r/a)=1(r/a)=0.9 (r/a)=1(r/a)=0.9

H-mode transition appears at 80 msecTime window of TVCX measurement is 20 msec

5/7

New H-mode Discharge for High Density Plasma

ECHNBI.#1NBI.#2Puff

#129874(a)

0

5

10

15

Ne

(x1

019

m-3

)

(b)

0

5

10

Wd

ia(k

J) (c)

(d)

0

0.2

0.4

0.6

0 50 100 150 200

P.r

ad

(M

W)

(e)

Time (msec)

High electron temperature and high electron pressure were sustained at plasma edge region

High performance H-mode was triggered by stopping strong gas puff

Edge electron temperature and density at (r/a) = 0.7

Central electron temperature and density at (r/a) = 0.0

Stopping gas puff

1st L-H 2nd L-HBack transition

2.5

2

1.5

1

0.5

0pre

ssu

re (

x1

01

9 k

eV

m-3

)

16012080400

Time (ms)

12

8

4

0

n e (

x1

01

9m

-3)

0.30

0.20

0.10

0.00

Te

(keV

)

=0.7

5

4

3

2

1

0

pre

ssu

re (

x1

01

3 k

eV

cm

-3)

16012080400Time (ms)

12

8

4

0

n e (

x1

01

9m

-3)

1.0

0.8

0.6

0.4

0.2

0.0

Te

(keV

)

=0.0

ETB

L-modeReheat with ETB

Reheat

L-modeReheat with ETB

ETB ReheatETB

L-modeReheat with ETB

ReheatETB

L-modeReheat with ETB

Reheat

High performance H-mode

H-mode

6/7

H-a

lpha

Summary of CHS Transport Barrier Physics Experiment

1. In the internal transport barrier (ITB) experiment, new diagnostic for ion temperature gradient measurement showed a steep gradient of 13 keV/m. ITB locations are different for electrons and ions.

2. In the edge transport barrier (ETB) experiment, negative radial electric field (~ 10 kV/m) was measured at the plasma edge by the charge exchange spectroscopy. Electric field shear of 2 MV/m2 is created, which is strong enough to suppress the turbulence.

3. New high performance H-mode was found for high density plasma (Ne~ 1 x 1020 m-3) with gas puff control. High electron temperature and high electron pressure were created at plasma edge.

7/7

Collaboration Research Program between CHS and Heliotron J Groups

Overdense Plasma Heating by O-X-B Mode Conversion

0

4

8

12

0 50 100 150 200

line

ave

. ele

ctro

nde

nsit

y (x

1019

m-3

)

time (ms)

0

400

800 #129212

ECH NBI gaspuff (a.u.)

pow

er (

kW)

012345

0

400

800

plas

ma

stor

ed

ener

gy (

kJ)

radi

atio

n (k

W)

0

100

200

300

0

0.2

0.4

0.6

0.8

1

-16 -14 -12 -10 -8 -6 -4 -2 0

Lea

kag

e E

C p

ower

(a.

u.)

Wp (

kJ)

EC-wave incident angle (deg)

#127704-713

• Evident increase in stored energy has been observed by applying 54.5 GHz ECH in overdense NBI plasmas on CHS

• The electron density exceeds the O-mode cut-off, nec=3.7x1019m-3

• The EC injection angle for max Wp is close to a predicted O-X conversion point

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500

#129203-213

Wp

(k

J)

EC-wave injection power (kW)

Collaboration Research Program between CHS and Heliotron J Groups

Studies for Fast Ion Transport Induced by MHD modes

00.5

1

0 0.2 0.4 0.6 0.8 1r/a

0

50

100

150

200

250

n=2

n=1

1/q

Fre

qu

enc

y (k

Hz)

0

2

ECHNBI(Co)

0

1

200 220 240 260 280 300time (ms)

HIS

m~3/n=2

m=4/n=2m~2/n=1

Fre

q. (

kHz)

100

0

Wd

ia (k

J)

Heliotron J #21145, b = 0.16, Bt =1.36T

Comparison of shear Alfvén spectra between CHS and Heliotron J

I H

,IIS (

A.U

.)

Heliotron J•Weak magnetic shear.•Shear Alfvén continua cannot couple with each other.

Bursting GAEs in Heliotron J•Bursting GAEs (m=4/n=2, f = 40~70 kHz) appeared in Co-injected NB plasmas at high b configuration.• Simultaneous bursts in ion saturation current and H signal support the existence of the outward particle flux. •Installation of directional Langmuir probe** for energetic ion measurements is planned.**K. Nagaoka, et al., PFR Vol. 1 (2006) 005

CHS•Moderate negative magnetic shear.•TAE gaps formed by the poloidal mode coupling exist on.

GAEs (global AEs)

TAEs or EPMs(toroidal AEs)

* M. Isobe, et al. EX/P6-8