JAERI

T. Nakano, N. Asakura, H. Takenaga, H. Kubo, Y. Miura, S. Konoshima, K. Masaki, S. Higashijima

and the JT-60Team

Japan Atomic Energy Research Institute, Ibaraki, Japan.

Impact of nearly-saturated divertor plates on particle control

in long and high-power-heated discharges in JT-60U

20th IAEA Fusion Energy ConferenceVilamoura, Portugal, 1-6 November 2004

JAERI Background

ISSUE: Experience and knowledge of operation with Rrecycling ~ 1

JT-60Sec.

Long pulse, steady-state operation

JT-60NCTMin.

ITERMin.~ Hour

DEMODay - Year

ConditionedRrecycling < 1

UnconditionedRrecycling ~ 1 or >1(Wall saturation)

wall

15s => 65sa

JAERI IntroductionParticle control; For a constant density Fueled = Pumpedaaaaaaaaaaaaaaaa

Short pulse:Divertor-pumping

+Wall-pumping

Long pulse:Divertor-pumping

+ (Co-deposition?)

Long pulse in JT-60Pheat~12 MW, 30s

Particle control at wall saturated

First w

all

Gas-puffPellet

NB

Core Plasma

Baffle

Divertor-Pumping

BafflePlates

Divertor

JAERI Outline

2.0

1.0

0.0

x101

9

403020100Time (sec)

20

10

0 RG

as

( P

am3 /

s)

n e (

x 1

019 m

-3 )

Gas

ne

1.0

0.5

0.0

x102

0

D

( a.

u. )

1.0

0.0

I p (

MA

)

10

0

PN

B (

MW

)

P-NB

N-NB

Ip

E043178

•Density controllability

w at wall

saturation

•Identification

of wall saturation

•Summary

JAERI No “carbon bloom”

Energy Input : 350 MJ

Div. surface temperature : ~ 1300 K

0.4

0.2

0.0

C V

I in

tens

ity (

a.u

.)

3002001000Input Energy ( MJ )

Open divertorW-shaped divertor( ~ 1999) ( ~ 2004)

JAERI

Identification of Wall Saturation

JAERI

8

6

4

2

0

x102

2

403020100Time ( sec )

Injected ( NB + Gas )

Pumped

WallPar

ticle

s (

x 1

022

)

4

2

0

x102

1 (

x 1

021

/ s )

PumpGas

E043860

420

x102

0

1050

1050

x102

0 N-NB

P-NB

( M

W ) ( x 10

20/ s )

1.0

0.5

0.0

4

2

0x10

19 n e

Ip

( x 10

19

m-3)

( M

A )

Wall Saturation identified in long pulse operation

t = 20 - 27s, constant wall retention Wall saturation ELMy H-mode Zeff ~3,H89PL~1.7Then, MARFE ( detach )

MARFE

Saturation

Quasi-steady-state, Vp dnp/dt ~ 0, Vn dnD0/dt ~ 0, Rwall = RP-NB + RN-NB

+ RGas - Rpump

JAERI Saturation Area, Wider than Divertor platesParticle Balance between pulses •Until 44018,

Wall retention increases•Wall saturation•After 44019, 3x1022 are released. 3x1022

Saturation level of D+ to C tile at 300eV = 1x1021m-2 Saturation area (Minimum) = 3x1022/ 1x1021m-2

= 30 m2

> Divertor plates ( 20 m2 )

1.0

0.5

0.0

x102

3

201510Time (sec)

Injected ( NB + Gas )

Pumped

Wall Retention

Par

ticle

s (

x 10

23 )

•During 44020, 3x1022 retained in walls.Active wall-pumping capacity ~ 3x1022

Particle Balance during 44020

1.5

1.0

0.5

0.0Par

ticle

s (

x 10

23 )

440204401944018440174401644015Shot Number

Injected

Pumped

JAERI

6 6

3 3

0 0

x102

1

353025201510Time ( sec )

Rw

all

( x1

021 /

s )

10 10

5 5

0 0

-5 -5x1

022 Injected ( NB )

Wall Retention

Pumped

Twall = 520 KIdentical discharge condition;

Ip,Bt,ne,PNB,H89PL,Tsurfdiv

,,,

Release-Rate from walls

Significant Particle Release at Twall = 520 K

Twall = 420 K

The only difference : first-wall-temperature Suggests particle release from first wall / Baffle plates

Gas-Puff-Rate6

3

0

x102

1

201510Time ( sec )R

ga

s (

x 10

21 /

s )

10

5

0

-5

x102

2

Injected ( NB + Gas )

Pumped

Wall Retention

Par

ticle

s (

x 10

22 )

JAERI

1017

1018

1019

1020

1021

Inte

nsi

ty (

ph

/ sr

m2 s

)

222018161412108642

Viewing Chord ( ch )

Source of particles, Baffle Plates

Twall= 420 K Twall= 520 K

Divertor similar

First wall >

Baffle <

1ch

8ch

11ch 20ch

19ch

Viewing chord for DDivertorInnerBaffle

OuterBaffle

Main ChamberFirst wall

D Brightness

Twall = 520 KNo gas-puff

Twall = 420 KGas-Puff

JAERI

Density Controllability by

Active Divertor-Pumping

at Wall Saturation

JAERI

PumpingG

AP

x1019

Density controllability of divertor-pumping

GAP 9.5 cm 4.5 cm

P0 + ~ 0, -

ne >

Wall saturation

3

2

1

0

x101

9 n e

( x

10

19

m-3

)

0.12

0.08

0.04

0.00

Pre

ssur

e (

Pa

)

30252015105Time ( sec )

Pe

nning

gag

e

Suggests;Large GAP => Increase of P0 => Increase of ne

With Gas-puff

No gas-puf

JAERIHigh pumping-rate suppresses increase of plasma particles

Difficult to prevent undesirable density rise of high plasmas ( Large GAP )

Limited period of high N; ex. 22.3 s for N = 2.3Higher pumping-rate is required even for

low plasmas ( Small GAP )

Condition : wall saturationDensity : ne/ne

GW = 62-66%

Decreasing Gap

2

1

0

x101

9

543210x10

21

d N

i / d

t (

x 10

19 /

s )

Pumping-Rate ( x 10 21

/ s )

Wall-pumping effective

JAERIControllability of detachmentby divertor-puming at R = 1

SOLDOR simulation

RPum

p

6x10 21/s

Rrecycle =1

3x1021/s10 MW

e = i = 1 m2/s, D = 0.3 m2/s

Indicates higher pumping speed by a factor of 2 - 3 can avoid MARFE at the end of long pulse discharges

R Gas

3x1021 /s

Pumping speed 25m3/s 50m3/s

P0OutDiv 2.0 Pa 1.2 Pa

neOutDiv 4x1020m-3 2x1020m-3

TeOutDiv 0.8 eV 9.7 eV

1.0

0.5

0.0Pre

ssur

e R

atio

1007550250Pumping Speed ( m

3 / s )

JT-

60U

14

.8 m

3 /s

Detach AttachInter-mediate

( D

iver

tor

/ M

idpl

ane

)

JAERI Summary• Modification for Long Pulse Operation, 15 sec => 65 sec• ELMy H-mode plasma

( ~30 s ,~ 12 MW, 350 MJ, No “carbon bloom”)• Wall saturation was identified

(Minor role of co-deposition)

Divertor plates

Wall/baffle plates <= important particle source at Rrecy > 1

• No sudden changes of plasma ( Zeff, H89PL )

• Undesirable increase of plasma density

=> Confinement Degradation, MARFE• Higher divertor-pumping efficiency ( x 2 - 3 )

required to avoid MARFE

NB 10 sec => 30 sec