japan atomic energy agency naka fusion institute

Japan Atomic Energy Agency Naka Fusion Institute

H. Urano, N. Oyama, K. Kamiya, Y. Koide, H. Takenaga, T. Takizuka,

M. Yoshida, Y. Kamada and the JT-60 Team

21st IAEA Fusion Energy ConferenceChengdu, China, October 16–21, 2006

Enhanced H-mode Pedestal and Energy Confinement by Reduction of

Toroidal Field Ripple in JT-60U

EX/5-1

IntroductionSufficiently high pedestal pressure is required for favorable energy confinement in ELMy H-mode plasmas.

The effect of large TF ripple has been pointed out. Losses induced by TF ripple enhances the toroidal rotation (VT) in counter-direction.

To reduce TF ripple and increase VT into co-direction, the ferritic steel tiles (FSTs) have been installed in JT-60U.

Energy confinement in JT-60U tends to be relatively unfavorable particularly at larger volume plasmas.

Pabs = 7-10MW (co+perp.-NBI)ELMy H-modes

40 50 60 70 80

Vp [m3]

0.6

0.7

0.8

0.9

1

1.1

1.2

HH

98

(y,2

)

Comparing between H-mode plasmas with and without FSTs, the characteristics of pedestal and ELM activities due to the reduction of TF ripple and the variation of VT are investigated in JT-60U.

Objectives

Large Vp (~75m3): TF Ripple < 2.0% w/o FSTs

TF-ripple contour3.0%2.5%2.0%1.5%1.0%0.8%0.6%0.4%0.2%

BT = 2.6T

Pedestalheight

Core EdgePedestal

sepa

ratr

ix

Divertor

ELM

Shoulder

Pedestal Width

p

TF rippleToroidal rotation

TF

Rip

ple

-2

-1

0

1

2

0 /2 3/2 2

tor [rad]

r [%

]

Outline

1. Introduction

2. Objectives

3. Plasma performance after the installation of FSTs

4. Effect of toroidal rotation and TF ripple on the pedestal and ELMs

5. Energy confinement

6. Summary

-1

0

0 1r/a0

2

4

6

0 1

0

1

2

3

4

0 10

2

4

6

8

0 1r/a

r/a

r/a

VT [

105m

/s]

ne [

101

9m

-3]

Te [

keV

]T

i [ke

V]

with FST

w/o FST

w/o FST with FST

1.2MA / 2.6T (q95 = 4.1) Large Vp(~75m3)

Energy confinement improved by the installation of FSTs

Pabs ~ const.

Perp.NB

Even at a given Pabs, energy confinement is improved with FSTs.

Profile of VT shifts towards co-direction with FSTs at ~fixed Pabs.

The Te and Ti profiles are increased in whole range of minor radius by FSTs.

Pabs ~ 8.3 MW

3.0 4.0 5.0 4.0 5.0 6.0 7.0 8.0 9.0

time [s] time [s]

0

2

1

02

1

010

5

0

03

2

0

1

E044292 E046426

[MW

][M

J][a

.u.]

[keV

]

[1020

m-2

]

PNBIPNBI

WDIAWDIA

neTL ne

TL

D D

Ti (r/a=0.2)

Ti (r/a=0.8)

Ti (r/a=0.2)

Ti (r/a=0.8)

co-NBI co-NBI

15

10

5

co

ctr

0

0.1

1.92

2.02

5.3 5.4 5.5

44292

time [s]

Wd

ia [

MJ

]

D [

a.u

.]

0

0.1

2.06

2.16

7.8 7.9 8

46426

time [s]

Wd

ia [

MJ

]

D [

a.u

.]0

1

2

-0.0500.050.10.15

distance from separatrix [m]

Ti [

keV

]

w/o FST

with FST

Pedestal and ELM

with FST

w/o FST

Higher pedestal Ti is obtained in case with FSTs accompanied by wider pedestal width.

ELM energy loss becomes larger while ELM frequency decreases. Inter-ELM dW/dt increased at a constant Pabs.

w/o FST (Pabs = 8.4MW, VTped = -52km/s):

fELM = 70Hz, WELM = 18kJ

with FST (Pabs = 8.2MW, VTped = -21km/s):

fELM = 51Hz, WELM = 34kJ

Large Vp(~75m3)

-1

0

1

0 2 4 6

PLfast [MW]

VT

pe

d [

105m

/s]

PNBperp

with FST

w/o FST

co-NBI at large Vp

-1

0

1

0 2 4 6

PLfast [MW]

VT

pe

d [

105m

/s]

co-NBI at small Vp

Edge toroidal rotation enhanced into ctr-direction with increased fast ion loss

When fast ion loss is increased by perp-NBs, VT

ped is enhanced into counter-direction.

Effect of FSTs on VTped is the m

ost remarkable at large Vp with co-NBI.(No clear difference at small Vp)

0

20

40

60

80

100

-1 0 1

VTped [105m/s]

f EL

M [

Hz]

co-NBI with FSTco-NBI w/o FSTbal-NBI with FSTbal-NBI w/o FSTctr-NBI with FSTctr-NBI w/o FST

-1

0

1

0

20

40

60

80

100

0 2 4 6

Psep [MW]

[105

m/s

]

[Hz]

VTped

fELM

ELM frequency becomes lower with edge toroidal rotation into co-direction

Large Vp (~75m3) with FST

ne ~ 2x1019m-3

Psep ~ 5MW, ne ~ 2x1019m-3

Power dependence using perp-NBs of ELM frequency fELM involves the effect of VT in many cases.

(1) Power dependence (fixed VT at the pedestal)

At a given Psep, ELM frequency fELM is clearly reduced as the co-toroidal rotation is enhanced.

At a given VTped, ELM frequency fELM increases in

proportion to Psep.

(2) Toroidal rotation dependence (fixed Psep)

(type-I ELM)

The dynamic range of VTped is expanded towards

co-direction by the installation of FSTs.

ELM energy loss becomes larger when pedestal toroidal rotation increases into co-direction

With increasing toroidal rotation towards co-direction, ELM energy loss WELM clearly becomes larger with the decrease of fELM.

When VTped shifts towards co-direction, the ELM loss power tends to inc

rease slightly. In other words, the inter-ELM transport loss is reduced with VT

ped into co-direction.(Change of PELM/PSEP was small before the installation of FSTs.)

0

2

4

6

8

10

-1 0 1

VTPED [105m/s]

WE

LM

/ W

pe

d [

%] co-NBI with FST

co-NBI w/o FSTbal-NBI with FSTbal-NBI w/o FSTctr-NBI with FSTctr-NBI w/o FST

Psep ~ 5MW, ne ~ 2x1019m-3

Large Vp (~75m3)

Large Vp (~75m3)

0

10

20

30

40

50

-1 0 1

VTPED [105m/s]

PE

LM

/ P

se

p [

%]

ELM loss power

Inter-ELM

PELM = fELM WELM

0

2

4

6

8

10

-1 -0.5 0 0.5 1

VTped [105m/s]

pp

ed [

kPa]

Pedestal pressure tends to increase with toroidal rotation into co-direction at the plasma edge

0

2

4

6

8

10

-1 -0.5 0 0.5 1

VTped [105m/s]

pp

ed [

kPa]

Large Vp (~75m3)

Small Vp (~52m3)

Pedestal pressure increases with the increase of VT

ped into co-direction.

However, at large Vp config., higher pedestal pressure is obtained in case with FSTs at a given VT

ped.

At small Vp config., pedestal pressure is not changed by FSTs.

Since the effect of FST is less significant at smaller Vp config., reduction of TF ripple may affect the increase of the pedestal pressure.


The changes of ELM activities with VTped are mor

e sensitive than the change of pped.

H-mode pedestal becomes wider with enhanced VT into co-direction and reduced TF ripple

0

1

2

0

1

2

-0.0500.050.1 -0.0500.050.1


Tipe

d[k

eV]

pedestal shoulder

(A) co-NBI

(B) ctr-NBI

0 1r/a

VT

[10

5 m/s

]

(A) co-NBI

-2

-1

0

1

-2

-1

0

1

(B) ctr-NBI

Pabs ~ 6.5MW

neped ~ 1.5x1019m-3

Effect of toroidal rotation Effect of TF ripple

0

2

4

6

8

10

-1 -0.5 0 0.5 1

VTped [105m/s]

ppe

d [

kPa

]

Large Vp (~75m3)


(C)

(D)

(A)(B)

For both cases, pedestal width of Ti becomes wider while the change in the pedestal Ti gradient is unclear.

Compare the pedestal profiles with VT

ped into co- and ctr-direction at fixed TF ripple.Compare the pedestal profiles with large (w/o FST) and small TF ripple (with FST) at almost fixed VT

ped.

0 1r/a

VT [

105 m

/s]

(C) with FST

-2

-1

0

1

(D) w/o FST

0

1

2

0

1

2

-0.0500.050.1


T i[k

eV]

pedestalshoulder

(C) with FST

(D) w/o FST

Energy confinement improved with enhanced toroidal rotation into co-direction

As VT is enhanced into co-direction, HH-factor becomes larger for the case of the large Vp plasmas.

With the reduction of TF ripple by the installation of FSTs, higher HH-factor is obtained in case with large Vp plasmas.(The effect of TF ripple is small at the small Vp plasmas.)

0.6

0.7

0.8

0.9

1

1.1

1.2

-1 -0.5 0 0.5 1

VTped [105m/s]

Large Vp (~75m3)


HH

98

(y,2

)

Summary

The characteristics of pedestal and ELM activities due to the reduction of TF ripple and the variation of toroidal rotation were investigated in JT-60U.(1) By the installation of FSTs, enhanced pedestal pressure and energy c

onfinement are obtained at large volume plasmas.(e.g. HH98(y,2) = 0.84 -> 0.92 at r ~ 2% -> 1% for the case of co-NBI

s)(2) With increasing VT into co-direction, pedestal pressure tends to be rais

ed accompanied by wider pedestal width.(3) By the reduction of TF ripple, pedestal pressure is increased and the w

idth of the H-mode pedestal becomes wider.(4) When VT increases into co-direction in type-I ELMs, ELM frequency de

creases and ELM energy loss becomes larger. (The change of ELMs with VT is more sensitive than that of pedestal pressure.)

The poster of this talk will be presented on Friday afternoon (EX/5-1).

japan atomic energy agency naka fusion institute

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