ASIPP HT-7 belt limiter Houyang Guo, Sizhen Zhu and Jiangang Li Investigation of EAST Divertor...

ASIPP

HT-7 belt limiter

Houyang Guo, Sizhen Zhu and Jiangang Li

Investigation of EAST Divertor Asymmetry in Plasma Detachment & Target Power Loading

Using B2/Eirene

Seminar presented at AS-IPP, Hefei, 10/10/2006

Acknowledgements

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Jiangang Li, Baonian Wan, Yuanxi Wan,

Sizhen Zhu for support of this work.

Youzhen He, Weiping Huang, Qing Li,

Ying Zhang for facilitating my visit.

And all of you!

Introduction

HT-7 belt limiter

A major concern for EAST and future high- powered steady-state machines such as ITER is the power handling capability of divertor target plates.

Localized injection of highly radiating impurities such as Ne may provide as a means of reducing power fluxes to the divertor targets and actively controlling inner/outer divertor asymmetry in power loading.

Outline

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EAST divertor geometry and major modeling parameters for B2/Eirene – SOLPS4.0.

Basic performance of EAST divertor in terms of target power loading and impurity screening for both single-null and double-null configurations.

Active control of plasma detachment and target power loading using neon puffing.

Summary and conclusions.

Unique Features of EAST

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High power

1st phase: 10 MW

2nd phase: 20 MW

(with NB)

And Long pulse

1000 s, sustained by

LHCD

EAST was built to allow both single null and double null divertor operations

HT-7 belt limiter

Basic Divertor Functions

HT-7 belt limiter

Exhaust power and particles

(including helium ash in a reactor)

Provide sufficient screening for

impurities to minimize core

contamination

A major concern for EAST and ITER is divertor power handling capability

- Provided by Dr. Damao Yao

Modeling of Divertor Performance Using B2/Eirene – SOLPS 4.0

B2/Eirene code package – SOLPS 4.0

A multi-fluid code B2 for electrons and ions, and

A Monte-Carlo code Eirene for neutrals

Major control parameters

Total heat fluxes from confined core: Ps 4 MW (equally split between the i and e channels)Ps,out 3Ps,inn for double dull configurationns = 0.5 3.51019 m-3

ITER-like cross-field transport: D = 0.3 m2s-1

i e 1.0 m2s-1

Impurity Sources

(1) Intrinsic Carbon

Physical sputtering

Chemical sputtering

Ych = 2%

(2) Active neon puffing

To reduce target power loading

Control divertor inner/outer asymmetry

As expected, CDN reduces peaked heat fluxes to both targets.

Zs is also reduced for CDN.

However, plasma detaches at inner target occurs at a much lower density for CDN, thus resulting in strong divertor asymmetry.

Comparison between single null (SN) & double null (CDN) configurations

1

2

3

4

1.0 1.5 2.0 2.5

ns (1019 m-3)

Zs

3.0

hg2005.a

sipp_psi

17.6

d

0

2

4

q pk,

out(M

W m

-2) SN

CDN

0

2

6

4

qpk,

inn

(MW

m-2

)

Plasma is fully detached from inner target, with heat flux to the target dramatically reduced.

Heat flux at the outer strike point is substantially reduced - a key feature of vertical divertor, but remains high elsewhere. Localized gas puffing from outer divertor may accelerate detachment, further reducing heat flux to the outer divertor.

CDN operation leads to stronger divertor asymmetry

0

0

0

1

40outer

2

3

2

1

80

120

Te

(eV

)n

e(1

020 m

-3)

q tot(M

W m

-2)

-0.5 0 0.5 1.0

Separa

trix

1.5

Distance from separatrix (cm)

2.0

hg2

00

5.a

sip

p.9

a

inner

midplane

ns = 1.51019 m-3

Consequences of Divertor Asymmetry

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Full plasma detachment at inner target may lead to confinement degradation due to excessive neutral influxes around X-point to the core.

Further, most of the outer divertor plasma still remains attached, with substantial power flux going to the outer target, which is undesirable for long pulse operation.

Ne is introduced from outer lower divertor.

Ne is well restricted to the vicinity of lower divertor due to strong divertor screening for Ne.

However, significant radiation from neon is also present in the inner divertor, presumably due to leakage of Ne through private region or around X-point.

Localized neon puffing is used as a means to reduce heat flux to outer target

Ne

It is remarkable that neon puffing does not appear to affect much the edge impurity content, suggesting very strong divertor screening for neon under modeled conditions.

Nevertheless, Ne puffing dramatically reduces heat fluxes to the outer target

1

2

3

4

1.50.5 1.0 2.0

ns (1019 m-3)

2.5

hg2006.p

si17.2

bZs

0

2

1

3

q pk,

inn

(MW

m-2

)

Ne puffnoNe

0

2

1

3

4

qpk,

out(M

W m

-2)

To further reduce heat flux to the outer target and divertor asymmetry: Optimizing Ne puffing location to maximize Ne ionization inside outer divertor. Inducing SOL flow by mid- plane fueling & pumping. A physical septum may help preventing direct Ne leakage from outboard into inboard.

Work in progress: Reduce neon leakage into inner divertor

Summary & Conclusions

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A major concern for EAST and future high-powered steady-state machines such as ITER is the power handling capability of divertor target plates.

As expected, double null operation distributes output power more widely, reducing peak target power loading.

However, double null leads to early detachment at inner target, resulting in strong divertor asymmetry.

Ne puffing from outer divertor dramatically reduces peak heat flux to the target, without affecting much Zeff.

To further reduce outer target power loading and divertor asymmetry, Ne leakage into inner divertor must be minimized.