1

JFT-2M

Studies of HRS H-mode plasmain the JFT-2M tokamak

K. Kamiya1, H. Kawashima1, T. Ido2, N. Oyama1, M. Bakhtiari1, S. Kasai1,Y. Kusama1, Y. Miura1, H. Ogawa1, K. Tsuzuki1, K. Uehara1, and

JFT-2M Group

Electrostatic fluctuation and fluctuation-induced particle flux during formation of theedge transport barrier in the JFT-2M tokamakT. Ido2, Y. Miura1, K. Hoshino1, Y. Hamada2, Y. Nagashima2, H. Ogawa1,

K. Shinohara1, K. Kamiya1, A.Nishizawa2, Y.Kawasumi2, Y. Kusama1, andJFT-2M Group

1Japan Atomic Energy Research Institute2National Institute for Fusion Science

Presented at 20th IAEA Fusion Energy ConferenceVilamoura, Portugal, Nov. 1-6, 2004

EX/4-6Ra

EX/4-6Rb

JFT-2M

2

JFT-2M

Time [ms]

L H

WMHD

Dαααα

PNB

580 630 680 730

3210

30

15

02.

1.

0.[a.u

.]

[

KJ]

[MW

]

HRS

Introduction

“Geodesic-Acoustic-Mode”

(GAM)

“High Recycling Steady”(HRS) H-mode

(IAEA2002, Lyon)

-30 -20 -10 0 10∆∆∆∆T from L/H transition [ms]

5040302010

0

Fre

q. [

kHz]

HL

φφφφ ~15 kHz∼∼∼∼HIBP

-5 0 5 10 15∆∆∆∆T from HRS transition [ms]

HRSH500

400

300

200

100

0

Fre

q. [

kHz] Magnetic probe

Bp~350 kHz.

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JFT-2M

Outline

“Geodesic-Acoustic-Mode” (GAM) in L-mode• Characteristics

• Relation with ambient turbulence

• Contribution to particle flux

“High Recycling Steady” (HRS) H-mode regime• Global behaviors

• Pedestal characteristics and Role of edge MHD activities

• Access conditions in terms of dimensionless parameters

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JFT-2M

Potential and density fluctuations fromHIBP measurements in L-mode plasma

• A significant peak in bothpotential and density powerspectrums at fGAM ~ 15kHz

• Higher coherence between30–60 kHz

• Phase difference is about ππππ/2 ⇓⇓⇓⇓

Ambient fluctuation with 30-60kHz mainly contributes toparticle flux

HIBP

)(192

1kHz

M

TT

Rf

i

eiGAM =+=

π

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JFT-2M

Other observations also suggest thatoscillations are quite similar to GAM

kθθθθ ~ 0 cm-1

at fGAM

|φφφφ(fGAM)| has maximum at~3 cm inside Rsep (ρρρρ~0.85)

kr ~ 1 cm-1

at fGAM

|φφφφ(fGAM)| smallnear Rsep

⇓⇓⇓⇓ krρρρρi ~ 0.26<1

⇓⇓⇓⇓ m ~ 0

•Electrostatic (low m)acoustic mode (i.e. B~0)

•Large E, small n

~

V⊥⊥⊥⊥ =ExB/B2~ ~

E ~

n∝∝∝∝ -divV⊥⊥⊥⊥~ ~

•Linked with zonal flows,predicted by codes

~ ~

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JFT-2M

Significant coherence betweenφφφφGAM and envelope of nambient~ ~

Envelope> 30 kHz

Envelope> 80 kHz

envelope

envelope

⇔⇔⇔⇔

nambient~ ~nambient

nambient~

~

φφφφGAM

nambient

nambient

~

~

~

The modulation of nambientcorrelates with GAM

~

φφφφGAM

⇔⇔⇔⇔

nambient~

~φφφφGAM

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JFT-2M

Others

GAM

L-mode

Particle flux exhibits an intermittentbehavior associated with GAM

ΓΓf e

t

eHIBP

HIBP t

nEB

nI

IEB

== ==˜˜ ˜ ˜

,

,

θθ θθ0

0

HL L/H

⇒ Other mechanism may alsocontribute to intermittency

on the particle flux

Dαααα

IHIBP∝∝∝∝ ne

φφφφpotential

ΓΓΓΓflux

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JFT-2M

1

2

3

0.2 0.4 0.6

H89

P

ne/nGW

H89P~1.6 atne/nGW~0.6

0.1

1

10

10 100Neutral pressure [mPa]

I EL

M/I D

αααα ELMy

Mixture

HRS

Disappearance of large ELMs in “HighRecycling Steady” (HRS) H-mode regimeNew operating regime obtained after boronization⇒⇒⇒⇒ Essential to minimize erosion of the divertor tiles

-20 0 20 40 60 80 100∆∆∆∆T [ms]

-20 0 20 40 60 80 100∆∆∆∆T [ms]

-20 0 20 40 60 80 100∆∆∆∆T [ms]

-20 0 20 40 60 80 100∆∆∆∆T [ms]

Dαααα [a.u.]

HRS

ELMy

∆∆∆∆T: Time from L/H transition

Mixture

Mixture

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JFT-2M

Pedestal pressure for HRS was limitedat ~70% of ELMy discharge

⇒⇒⇒⇒ Edge MHD activities may keeppe,edge below the level needed to

induce a large ELM

0

0.3

0.6

0.9

0 1 2 3 4 5

T e,

edg

e [k

eV]

ne, edge [1019 m-3]

νννν*~0.2

νννν*~1.0

L-mode

νννν*~0.5

νννν*~2.0

νννν*~10.0

ELMy

HRS

Mixture

ννννe*~1.4HRS

500400300200100

Fre

q. [

kHz]

Dαααα

[a.u

.]

1.2

0.85

0.5

20 [ms]

Large ELMννννe*~0.2

Magnetic probe

Fre

q. [

kHz] 500

400300200100

Dαααα

[a.u

.] 1.5

0.9

0.3

20 [ms]

Bp~350 kHz.

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JFT-2M

Pedestal pressure for HRS was limitedat ~70% of ELMy discharge

0

0.3

0.6

0.9

0 1 2 3 4 5

T e,

edg

e [k

eV]

ne, edge [1019 m-3]

νννν*~0.2

νννν*~1.0

L-mode

νννν*~0.5

νννν*~2.0

νννν*~10.0

ELMy

HRS

Mixture

Magnetic probeat vessel wall

Steep IHIBP profile in ELM-free phasechanged into broader one for HRS⇒⇒⇒⇒ Enhanced particle transport

Density fluctuationlocalized at r/a~0.9

0

1

-0.1

0

0.1

0.8 0.9 1

I HIB

P [

×××× 0.1

µµµµA

]

I HIB

P/I H

IBP

r/a

~

~∝∝∝∝ ne/ne

∝∝∝∝ ne

HIBP- ELM-free- HRS

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Access conditions in q95-ννννe* space

ELMy (large ELMs)

ννννe* < 1 Mixture

ννννe* ~ 1 HRS (small ELMs)

ννννe* ≥≥≥≥ 1Operational limit reducedfor higer q952

3

4

5

6

0.1 1 10

ELMy (large ELMs)MixtureHRS (small ELMs)

q95

ννννe*νν

εεe18 95 e

e2 3/2

6.9 10q Rn ln

T∗∗ −−== ×× ΛΛ

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JFT-2M

Summary

Electrostatic fluctuations (GAM) in L-mode• The modulation of nambient correlates with GAM• Fluctuation induced particle flux exhibits an intermittent

behavior associated with GAM, though other mechanismmay also contribute to intermittency on the particle flux

HRS H-mode• Pedestal pressure for HRS is limited at its own critical

value below the level needed to induce a large ELM• HRS is associated with edge MHD activities• A high collisionality phenomena

~