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HT-7/EAST ASIPP

Oxidation wall conditionings on HT-7 and EAST superconducting tokamaks

J.S Hu, J.G Li, Y.P Zhao

EAST Team

hujs@ipp.ac.cn

Institute of Plasma Physics, Chinese Academy of Sciences,

Hefei, Anhui 230031, China

PSI-19, May 24-28, 2010, San Diego, California, USA

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Contributors

• EAST team– X.M Wang, Y.W. Yu, G.Z. Zuo, J. H, Li, J.H. Wu, Y. Chen, X.M

Gu, Z.W Wu, J Huang, S.Y Lin, L Wang, B.L Ling, B.Shen, Y.Yang, X.Z Gong, L Hu, J.Y Zhao, X.Gao, X.D Zhang, B.N Wan et al.

• Partially supported by JSPS -CAS core university program– NIFS, Kyushu Univ., Shizuoka Univ.

• Co-operations in ITPA-DSOL group• Funded by the National Nature Science Foundation o

f China under Contract No. 10705030.

HT-7/EAST ASIPP

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HT-7/EAST ASIPP

1. Introduction2. Comparison of varios oxidations in HT-7

• Thermo-oxidation, • O-GDC • O-ICR • Sample analysis• summary of oxidations• Characteristics of oxidation techniques

3. Comparison of oxidations between HT-7 and EAST4. Oxygen removal and plasma recovery5. Prediction for ITER6. Summary

Outline

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HT-7/EAST

1. Introduction

• The long-term retention of tritium fuel in fusion devices is one of the major problems in fusion technology.

• The ability to remove tritium from amorphous tritiated carbon layers in ITER will have an important impact on the machine operation and safety.

• Oxidation conditioning is one of potential solutions.• On hot walls in tokamaks for in-situ co-deposit removal, such

as in TFTR, TEXTOR, HT-7, AUG, EAST, DIII-D……• Lab. reserches on deposits removed from TFTR, AUG, JET, DII

I-D.

ASIPP

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Motivations• In a limiter machine - HT-7 with 20% carbon walls:

• Thermo-oxidation, O-GDC and O-ICR experiment on hot walls at 400-470K from 2004 to 2006

• In an ITER-relevant full superconducting tokamak - EAST with divertor configuration

• He/O-ICR on full metal walls at 420K in 2007• He/O-ICR on full carbon walls at a room temperature in 2009

Mian efforts:• In-situ co-deposit removal techniques;• Plasma recovery after cleanup;

• Comparison of various techniques for oxidation wall conditioning

• Comparison of O-ICR between HT-7 and EAST machines, including the influence of plasma facing materials

• Oxygen removal and plasma recovery• Prediction for ITER.

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2. Various oxidations on HT-72.1 Thermo-oxidation

•Low removal rate for D and C

•High O retention

•Oxidations is transient

•Not enough Twalls and O2 pressure

•Without pumping;

•Initial oxygen pressure is 0.7, 1.1, 9.3 and 32Pa.

1.1 Pa thermo-oxidation

HT-7/EAST ASIPP

J. Nucl. Mater., Vol.350(2006)9

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2.2 O-GDC

• High pressure is beneficial for C and D removal.

• Compared to He-GDC cleaning, O-GDC wall conditioning has a higher removal rate for H by a factor of about 2~4 and for C by a factor of 25.

• In a long O-GDC operation in 2005, the removal rates for H and C sustained very high for 9.5hrs, whereas it decreased for D.

HT-7/EAST ASIPP

J. Nucl. Mater., Vol.349(2006)160

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2.3 O-ICR in HT-7

Single pulse 2s on(20~100kW)Pulsed O-ICR(20kW)0.3s on/ 1.5s off

HT-7/EAST ASIPP

• O-ICR with pulsed waves (0.3s on and 1.2s off) seems better than with single wave.

• Compared to He-ICR, O-ICR has a higher removal rate for H-atoms by a factor of about 6 and for

C-atoms by a factor of 20.

Plasma Phys. Control. Fusion, Vol.47(2005)1271

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Higher RF powerHigher oxygen pressure

•Higher release of hydrogen and carbon; •Higher oxides productions;

He in He/O-ICR plasma, •Promote oxygen reaction•Reduce oxygen retention.

2.3 O-ICR in HT-7

HT-7/EAST ASIPP

Plasma Phys. Control. Fusion, Vol.48(2006)807

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2.4 Sample analysis

By ~71mins O-ICR cleanings,• Deposits were effectively removed.• H and D retention reduced ~80%. • Oxygen content increased <30%.

Without exposure

After 71min. He/O-ICR

HT-7/EAST ASIPP

Plasma Phys. Control. Fusion, vol49(2007)421

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Thermo-O O-ICR 4:1 He/O-ICR O-GDC

Parameters 32Pa 40kW, 9 × 10-2Pa 40kW, 9.8 × 10-2Pa 1.5Pa, 250V/4A

Highest removal rate

(1021atoms/h)

H-atoms ~6 for C

Only in <1min.

26.3 5 56.5

D-atoms 7.76 5.65

C-atoms 14.9 7.5 55.3

Oxygen absorbed rate

(1014O-atoms/cm2.min)

21.5 7.3 3.45 45.5

Oxygen Coverage

O-atoms/cm2

~1017 1.44 × 1017 2.45×1016 6.5 × 1017

2.5 Comparison of oxidations in HT-7

HT-7/EAST ASIPP

1. Thermo-O: with Bt; Access to all areas, specially to shadow ereas; low removal rate, but could be improved with high wall Temp.(e.g.350oC) and higher oxygen pressure(e.g.>1000Pa)

2. O-GDC: without Bt; On Line-of-insight surface, effecitive area larger than O-ICR, specially to far positions, such as pump ducts; limited O2 pressure; Continously High removal rate even on Low Twalls, high O retention

3. O-ICR: with Bt; On Line-of-insight surface; limited O2 pressure; Continously high removal rate even on Low Twalls, low O retention

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3. Oxidations between HT-7 and EAST3.1 O-ICRF in EAST

full metal walls at 400K Full carbon walls at room Temp.

Similar behaviors during oxidation, and similar influence of power, pressure, pumping speed and wall conditions.

HT-7/EAST ASIPP

J. Nucl. Mater., 390–391 (2009) 929

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•ICR power and Pressure: particle energy and plasma density•Plasma volume:plasma power density•PFCs materials and Plasma fuels : source of C, H, and D•Configration and Plasma facing surfaces:cleaning area•Pumping speed: particles exhaust•RF antenna: coulpling power•Wall temperatures: oxidation efficiency

3.2 1:1 He/O-ICRF betweenHT-7 and EAST

HT-7/EAST ASIPP

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3.3 Removal rates in 20kW 0.014Pa He/O-ICR

HT-7 EAST(metal walls) EAST carbon walls

plasma volume 2.6 16 16

plasma facing surfaces

12 60 60

plasma-facing material

20% carbon +SS Full SS Full carbon

plasma fuel D2 H2 D2

configuration Limiter divertor divertor

Antenna Single antenna at high field side both for ICWC and heating

Two dedicated at low field side specially for ICWC

Two dedicated at low field side specially for ICWC

Wall temperature 400-420K ~400K ~300K

Removal rates for C 1.9×1021atoms/h 1.3×1022atoms/h 1.5×1022atoms/h

Removal rates for H 2×1021atoms/h 2.5×1022atoms/h 4.1×1022atoms/h

RREAST/RRHT-7=VHT-7×SEAST×PSEAST/(VEAST×SHT-7×PSHT-7)~12.8

HT-7/EAST ASIPP

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HT-7/EAST ASIPP

•Higher oxygen pressure, more oxides produced, however higher retention.

•Higher oxygen retention in O-GDC than in O-ICR;

4.Oxygen retention, removal and plasma recovery4.1 Oxygen retention

•To reduce O-retention in O-ICR:

Lower oxygen pressure

High ratio of He:O2

High ICR power

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4.2 Oxygen removal

Both He-GDC and He-ICRF were effective for oxygen removal.

D2-ICR cleaning has a higher removal rate of O than He-ICR by a factor of 5-7.

Oxygen removal depended on oxygen retention on the walls, cleaning parameters.

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Fusion Eng.&Des., Vol.81/19(2006)2175Fusion Eng.&Des., Vol.82/2(2007)133

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4.3 Plasma recovery

•Plasma could be recovered, but tens disruptive shots(32-97) are required. •After oxidation, impurities increased and Ha decreased. •Impurities, such as C, O, decreased shots by shots. •In 2007 experiments, 1g Boronization after He/O-ICR made plasma recovery easily, Zeff~2.5 was got in the recovered plasmas.

Less O retention and boronization helps the plasma recovery.

HT-7/EAST ASIPP

Fusion Eng.&Des., Vol.83(2008)689

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5. Prediction for ITER

HT-7/EAST ASIPP

Device Series Parameters Removal rates for C (atoms/h)

Removal rates for H (atoms/h)

Estimated C removal rate for ITER with 3MW ICR (atoms/h)

HT-7 (20% carbon walls)

Pure O-ICR

(2004)

40kW,0.09 Pa 1.5×1022 2.6×1022 1.8×1025 (358g/h)

4:1 He/O-ICR

(2005)

40kW,0.098 Pa 7.5×1021 5.4×1021 8.9×1024 (177g/h)

1:1 He/O-ICR

(2005)

40kW, 0.06Pa 4.2 ×1021 4.0×1021 5.1 ×1024 (101g/h)

Pure O-ICR

(2006)

60kW, 0.05Pa 1.1×1022 1.4 ×1022 8.8×1024(175g/h)

EAST (metal walls)

1:1 He/O-ICR

(2007)

20kW, 0.07Pa 4.2 ×1022 7.8 ×1022 9.5 ×1024(189g/h)

EAST (carbon walls)

1:1 He/O-ICR

(2009)

20kW, 0.1Pa 2.6 ×1022 9 ×1022 5.9 ×1024(117g/h)

To remove 700g T in ITER, it would require 0.5~7hrs of wall conditioning with 3MW O-ICR discharges.

Assuming with a same oxygen pressure, mian factors, such as power density, cleaning surface and actively pumping, are linearity effect on the deposits removal.

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HT-7/EAST ASIPP

•Series oxidation experiments were carried out on HT-7 and EAST.

•O-GDC appeared to be the most efficient on HT-7. However, O-ICR was almost as good and could be applied with the magnetic field in ITER.

•O-ICR on both EAST and HT-7 revealed that power density, working pressure, plasma facing area and materials, pumping speed and wall temperatures were main factors influencing on the deposits removal.

•High power, low oxygen pressure and He in O-ICR are beneficial for reducing oxygen retention.

•Plasma discharges could be recovered by effective cleanings and boronization.

•To remove 700g T in ITER, it would require 0.5~7hrs by 3MW O-ICR cleanings.

•Oxidation treatment is one of the most promising methods for amorphous tritiated carbon layers removal for ITER.

summary

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HT-7/EAST ASIPP

Thank you for your attention!!