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HT-7/EAST

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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HT-7/EAST

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  1. 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

  2. HT-7/EAST ASIPP 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 of China under Contract No. 10705030.

  3. HT-7/EAST ASIPP Outline • Introduction • Comparison of varios oxidations in HT-7 • Thermo-oxidation, • O-GDC • O-ICR • Sample analysis • summary of oxidations • Characteristics of oxidation techniques • Comparison of oxidations between HT-7 and EAST • Oxygen removal and plasma recovery • Prediction for ITER • Summary

  4. HT-7/EAST ASIPP 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, DIII-D.

  5. Motivations • In a limiter machine - HT-7 with 20% carbon walls: • Thermo-oxidation, O-GDC and O-ICR experiment on hot walls at 400-470Kfrom 2004 to 2006 • In an ITER-relevant full superconducting tokamak - EAST with divertor configuration • He/O-ICR on full metal wallsat 420K in 2007 • He/O-ICR on full carbon walls at a room temperaturein 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.

  6. HT-7/EAST ASIPP 2. Various oxidations on HT-72.1 Thermo-oxidation • Without pumping; • Initial oxygen pressure is 0.7, 1.1, 9.3 and 32Pa. • Low removal rate for D and C • High O retention • Oxidations is transient • Not enough Twalls and O2 pressure J. Nucl. Mater., Vol.350(2006)9 1.1 Pa thermo-oxidation

  7. HT-7/EAST ASIPP 2.2 O-GDC J. Nucl. Mater., Vol.349(2006)160 • 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.

  8. HT-7/EAST ASIPP 2.3 O-ICR in HT-7 Pulsed O-ICR(20kW) 0.3s on/ 1.5s off Single pulse 2s on(20~100kW) • 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

  9. HT-7/EAST ASIPP 2.3 O-ICR in HT-7 • Higher RF power • Higher oxygen pressure • Higher release of hydrogen and carbon; • Higher oxides productions; • He in He/O-ICR plasma, • Promote oxygen reaction • Reduce oxygen retention. Plasma Phys. Control. Fusion, Vol.48(2006)807

  10. HT-7/EAST ASIPP 2.4 Sample analysis Without exposure By ~71mins O-ICR cleanings, • Deposits were effectively removed. • H and D retention reduced ~80%. • Oxygen content increased <30%. After 71min. He/O-ICR Plasma Phys. Control. Fusion, vol49(2007)421

  11. HT-7/EAST ASIPP • 2.5 Comparison of oxidations in HT-7 • 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) • 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; ContinouslyHigh removal rate even on Low Twalls, high O retention • O-ICR: with Bt; On Line-of-insight surface; limited O2 pressure; Continouslyhigh removal rate even on Low Twalls, low O retention

  12. HT-7/EAST ASIPP 3. Oxidations between HT-7 and EAST 3.1 O-ICRF in EAST Full carbon walls at room Temp. full metal walls at 400K J. Nucl. Mater., 390–391 (2009) 929 Similar behaviors during oxidation, and similar influence of power, pressure, pumping speed and wall conditions.

  13. HT-7/EAST ASIPP 3.2 1:1 He/O-ICRF betweenHT-7 and EAST • 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

  14. HT-7/EAST ASIPP 3.3 Removal rates in 20kW 0.014Pa He/O-ICR RREAST/RRHT-7=VHT-7×SEAST×PSEAST/(VEAST×SHT-7×PSHT-7)~12.8

  15. HT-7/EAST ASIPP 4.Oxygen retention, removal and plasma recovery4.1 Oxygen retention • Higher oxygen pressure, more oxides produced, however higher retention. • Higher oxygen retention in O-GDC than in O-ICR; • To reduce O-retention in O-ICR: • Lower oxygen pressure • High ratio of He:O2 • High ICR power

  16. HT-7/EAST ASIPP 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. Fusion Eng.&Des., Vol.81/19(2006)2175 Fusion Eng.&Des., Vol.82/2(2007)133

  17. HT-7/EAST ASIPP 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. Fusion Eng.&Des., Vol.83(2008)689

  18. HT-7/EAST ASIPP 5. Prediction for ITER Assuming with a same oxygen pressure, mian factors, such as power density, cleaning surface and actively pumping, are linearity effect on the deposits removal. To remove 700g T in ITER, it would require 0.5~7hrs of wall conditioning with 3MW O-ICR discharges.

  19. HT-7/EAST ASIPP summary • 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.

  20. HT-7/EAST ASIPP Thank you for your attention!!

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