Deuterium retention on HT-7 with full metal PFMs

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ASIPPASIPPHT-7HT-7HT-7HT-7

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Deuterium retention on HT-7 with full metal PFMs

H.Y. Wang, J.S. Hu, X. Gao, B. Cao

Institute of Plasma Physics, Chinese Academy of Sciences, China

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outline

• Introduction– Retention in tokamaks– Motivation– Method: Particle balance

• Retention in various materials– Molybdenum PFMs– Lithium PFMs– Boron PFMs

• Summary

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Retention in tokamaks

• Fuel retention on walls would lead recycling and density

control problem which would terminate plasma

discharge, specially in a long plasmas required in future

SSO fusion devices;

• Fuel retention would also cause safety problem, such as

T operation in ITER.

• In 2011, HT-7 PFMs was changed from C to Mo, and Li

coating become main method for wall conditioning.

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Motivation

• Investigation of D retention on different plasma facing materials, such as Mo, Li and B coated films.

• Comparison with the previous retention on doped graphite on HT-7. – Realize the PFMs influence on fuel retention.

– Provide data accumulation for EAST(PFM will be Mo/W) and ITER.

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Method

• Particle Balance (PB)– Real-time

– Global inventory

– Couldn’t give location of retention

• Post-mortem Analysis (PA)– Location of retention

– Accumulated retention

– Couldn’t tell inventory of one shot or one day

SdtPQ

VPQ

QQQ

vvextract

tanktankpuff

retentionextractpuffl

During 2011 campaign of HT-7:

Mo tiles: 1.28m2

Li coating: 28 times (totally 350g)

1 boronization following Li

coatings

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outline


• Retention in various materials– Molybdenum PFMs– Lithium coating PFMs– Boron PFMs

• Conclusion

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2.1 Retention on Mo tiles

• In beginning shots, D release from walls due to disruptions.– D retention during D wall conditioning before plasma operation;– Most of plasmas was disrupted at low current ， I<90KA, t<1s.– Very small fueling, <30Pa.l

• After ~100 plasma discharges, the retention ratio increased, but lower than ~10%.

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2.2 Retention on Li coated films

• After Li coating– Retention ratio increased (Mo).– Required more fueling.

After the 4th Li coating, the retention ratio increased 20%.

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• After each coating, high retention ratio on fresh films, then it decreased slowly to a steady value;

• Steady retention ratio after each coating also increased with increasing of coated Li quantity.

The 27th time lithium coating

Fueled gas: 1000~1500 Pa.l

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2.3 Retention on B films

• Boronization:

– Followed 28 Li coatings

– 3g C2B10H12

• After the boronization,

– Abundant H released (80% in

pumped gases);

– H/(H+D) raised from 20% to

80%;

– Increase retention ratio, possible

due to H-D exchange;

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• The inventory divide by plasma length is called retention rate• Although the Li films stable retention ratio is higher than the boron's,

their stable retention rate is almost same (400 Pa.l/s).• The H/(H+D) can explain this well.

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Accumulated influence

• The retention fuel increased shot by shot, there is no signal of saturation (Li, B films).

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Comparison (HT-7)

Material Graphite Mo Li film B fresh film

Puffed gas (Pa.l) ? ~30 200-1500 200-800

ratio (%) 60 <10 40-75 70-80

Rate (D atom/s) 2*1022 <5*1019 0.4-1.2*1022 2.5-4*1021

Main mechanism Co-deposition

Absorption

Implantation

Implantation

Absorption

Li-D reaction H-D exchange;

Absorption

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outline


• Retention in various materials– Molybdenum PFMs– Lithium coating PFMs– Boron PFMs

• Summary

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Summary

• We have systemically investigate D retention on various walls, such as Mo, Li and B coated films, in 2011 campaign of HT-7;

• Compared with Mo (possible W), it was found Li and B films, also C has a high retention ratio for D retention;

• The different of the retention on various walls maybe reveal its various mechanism;

• This research would give same reference for D retention on Mo walls in EAST, and data accumulation for T retention in ITER.

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Thanks for your attention!

Acknowledgments• This research is funded by National Magnetic

confinement Fusion Science Program under contract 2010GB104002 and the National Nature Science Foundation of China under contract 11075185.

• Thank Bernard PEGOURIE from IRMF for his useful discussion for some basic issues.

Deuterium retention on HT-7 with full metal PFMs

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