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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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


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


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

  • Identification

  • of wall saturation

  • Density controllability w at wall saturation

  • Summary


No “carbon bloom”

Energy Input : 350 MJ

Div. surface temperature : ~ 1300 K


Identification of Wall Saturation


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 )


  • 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 )


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


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


Density Controllability byActive Divertor-Pumpingat Wall Saturation


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

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 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

  • 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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