Impact of nearly-saturated divertor plates
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T. Nakano , N. Asakura, H. Takenaga, H. Kubo, Y. Miura, S. Konoshima, K. Masaki, S. Higashijima PowerPoint PPT Presentation


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Impact of nearly-saturated divertor plates on particle control in long and high-power-heated discharges in JT-60U. 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.

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

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T nakano n asakura h takenaga h kubo y miura s konoshima k masaki s higashijima

Impact of nearly-saturated divertor plates

on particle control

in long and high-power-heated discharges

in JT-60U

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.

20th IAEA Fusion Energy Conference

Vilamoura, Portugal, 1-6 November 2004


Background

15s => 65s

a

Background

Long pulse, steady-state operation

DEMO

Day - Year

ITER

Min.~ Hour

JT-60

Sec.

JT-60NCT

Min.

twall

Unconditioned

Rrecycling ~ 1 or >1

(Wall saturation)

Conditioned

Rrecycling < 1

ISSUE: Experience and knowledge of operation

with Rrecycling ~ 1


Introduction

Baffle

Baffle

Divertor-Pumping

Plates

Divertor

Introduction

Pellet

Particle control;

For a constant density

Fueled = Pumped

aaaaaaaaaaaaaaaa

Short pulse:

Divertor-pumping

+

Wall-pumping

Long pulse:

Divertor-pumping

+

(Co-deposition?)

Gas-puff

NB

Core Plasma

First wall

Particle control

at wall saturated

Long pulse in JT-60

Pheat~12 MW, 30s


Outline

Outline

  • Identification

  • of wall saturation

  • Density controllability w at wall saturation

  • Summary


No carbon bloom

No “carbon bloom”

Energy Input : 350 MJ

Div. surface temperature : ~ 1300 K


Identification of wall saturation

Identification of Wall Saturation


Wall saturation identified in long pulse operation

Saturation

Wall Saturation identified in long pulse operation

MARFE

  • Quasi-steady-state,

  • Vp dnp/dt ~ 0,

  • Vn dnD0/dt ~ 0,

  • Rwall = RP-NB + RN-NB

  • + RGas- Rpump

  • t = 20 - 27s,

    constant wall retention

  • Wall saturation

  • ELMy H-mode

  • Zeff ~3,H89PL~1.7

    Then,

  • MARFE ( detach )


Saturation area wider than divertor plates

  • During 44020,

  • 3x1022 retained in walls.

  • Active wall-pumping

    capacity ~ 3x1022

Saturation Area, Wider than Divertor plates

Particle Balance between pulses

  • Until 44018,

  • Wall retention increases

  • Wall saturation

  • After 44019,

  • 3x1022 are released.

3x1022

Particle Balance during 44020

Saturation level of

D+ to C tile at 300eV

= 1x1021m-2

Saturation area(Minimum)

= 3x1022/ 1x1021m-2

= 30 m2

> Divertor plates ( 20 m2 )


Significant particle release at t wall 520 k

Twall = 520 K

Identical discharge condition;

Ip,Bt,ne,PNB,H89PL,Tsurfdiv,,,

Release-Rate from walls

Significant Particle Release at Twall = 520 K

Twall = 420 K

Gas-Puff-Rate

  • The only difference : first-wall-temperature

  • Suggests particle release from first wall / Baffle plates


Source of particles baffle plates

Viewing chord for Da

1ch

8ch

20ch

11ch

19ch

Source of particles, Baffle Plates

Da Brightness

Main Chamber

First wall

Inner

Baffle

Outer

Baffle

Divertor

Twall = 520 K

No gas-puff

Twall = 420 K

Gas-Puff


T nakano n asakura h takenaga h kubo y miura s konoshima k masaki s higashijima

Density Controllability byActive Divertor-Pumpingat Wall Saturation


Density controllability of divertor pumping

Suggests;

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

Density controllability of divertor-pumping

Penning gage

Wall saturation

GAP

Pumping

With Gas-puff

No gas-puf


High pumping rate suppresses increase of plasma particles

High pumping-rate suppresses increase of plasma particles

Condition : wall saturation

Density : ne/neGW = 62-66%

Decreasing Gap

  • Difficult to prevent undesirable density rise of

  • high d plasmas ( Large GAP )

  • Limited period of high bN; ex. 22.3 s for bN = 2.3

    Higher pumping-rate is required even for low d plasmas ( Small GAP )


Controllability of detachment by divertor puming at r 1

Controllability of detachmentby divertor-puming at R = 1

SOLDOR simulation

RGas

3x1021/s

3x1021/s

10 MW

Rrecycle=1

RPump

6x1021/s

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


Summary

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


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