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Lithium coating and its influence on plasma performance on HT-7

Lithium coating and its influence on plasma performance on HT-7 Z. Sun, J.S. Hu, G.Z. Zuo, J.G. Li ASIPP 2011-7-20. Outline. Introductions Lithium(Li) coating system Main Results Comparison with following boronization Summary. 1 Introductions.

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Lithium coating and its influence on plasma performance on HT-7

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  1. Lithium coating and its influence on plasma performance on HT-7 Z. Sun, J.S. Hu, G.Z. Zuo, J.G. Li ASIPP 2011-7-20

  2. Outline • Introductions • Lithium(Li) coating system • Main Results • Comparison with following boronization • Summary

  3. 1 Introductions • Li has good properties, such as low Z, strong getter of C, O and H isotopes. • Li coating is a better way to reduce impurities, control recycling and H content. • Controlling H content is useful for the different mode of ICRF heating. • Li coating is beneficial for plasma performance enhancement. • On the Mo wall Li coating maybe increase its effect on plasma performance. Changed graphite limiter to Mo limiter in HT-7 in this campaign

  4. Outline • Introductions • Li coating system • Main Results • Comparison with following boronization • Summary

  5. 2.1 Configuration of Li coating system • Two oven system for pre-coating: • Two ovens were shifted from EAST in 2010 for uniform coating; • Deeply movable to the center of inner vessel for enlarge coating surface. • One lithium dropper for active Li coating from PPPL . • Movable liquid lithium limiter. Reported by Dr. Zuo in this meeting Two lithium oven systems Lithium dropper Lithium oven Lithium limiter Lithium limiter Lithium dropper

  6. 2.2 Techniques of Li coating in HT-7 Red discharge zone during ICRF Li coating in HT-7 • Li coating 28times ~350g • Li injection 3 times • Liquid Li limiter Exp. 5 times • Boronization 3g • By evaporation, associated by He-GDC or He-ICRF discharge； • Evaporated at 500~590oC； • 1~2Hr./coating; • 5~30g/coating; • 1~2 times coating/day; • GDC: 3A • ICRF: 5~20kW

  7. Outline • Introductions • Li coating system • Main Results • Comparison with following boronization • Summary

  8. 3.1 Main results of Li coating • Reduce impurity radiation; • Decrease H/(H+D) to below 10%; • Lower particle recycling； • Fast plasma recovery after leaks; • The lifetime of Li film is 60~100shots; • Improve plasma performance； • Control H/(H+D) to convert ICRF heating mode, and to improve ICRF minority heating efficiency； • Increase plasmas reproducibility.

  9. 3.2 Reduce impurities and recycling • By Li coating, • C and O impurities decreased step by step; • Mo impurity also was suppressed; • Low Recycling plasma was easily obtained; • Li emission intensity increased every time; • Improve plasma performance • Radiation decreased significantly • Te increased

  10. Mo impurity was also suppressed by Li coating again and again Ip~150kA, Ne~1.5X1019/m3，Bt=1.9T Before and after 25th Li coating

  11. 3.3 Decrease H/(H+D) ratio • Control H/ (H+D) ratio for convertingdifferent ICRF heating mode • H/ (H+D) could be controlled in the range of 5-10% for improvement of ICRF minority heating efficiency;

  12. 3.4Control H/(H+D) for various ICRF heating mode ~ 20%(No.113388) mode conversion heating ~7% (No.113527) minority heating H/(H+D) Ti>0.8 kev Ti<0.6 kev Ip~150kA, ne~1.1×1019m-3，PICRF~750kW，Phase 180 °Bt~1.95T

  13. 3.5 Fast plasma recovery after leak • When the HT-7 vessel leaked air to 100Pa,repeatable plasma could be got just using 30g Li coating. • impurities radiation didn’t increase. • H/(H+D) recovered to previous ratio via 100 shots • Air leaked to 100Pa on about 330g Li coated walls is not a serious problem.

  14. 3.6Increase plasma reproducibility *the ratio of normal to total plasma discharges • Lithium coating increased the percentage of effective plasmas step by step.

  15. 3.7Lifetime of Li coating • Possibly due to Li consumption • (depended on Li coating and plasma operation) • LiI emission intensity decrease shot by shot after Li coating; • Impurities, include CIII, OII, MoI emission increase with LiI emission intensity decreasing; • Plasma performance decrease • Normally, the lifetime of Li film is for about 60-100 discharges.

  16. 3.8 Distribution of Li film With suitable arrangement of ovens and liquid lithium limiter • It seemed Li was coated on all limiters and Liners after exposure. • The Li film near oven seemed thicker than other surface. • contribution from liquid lithium limiter. Before li-coating After li-coating The Li film on the movable Mo limiter

  17. Outline • Introductions • Li coating system • Main Results • Comparison with following boronization • Summary

  18. 4.1Results of the following boronization Boronization with 3g C2B10H12 was carried out by ICRF discharge after 28 Li coatings. After boronization on the Li wall: • The Li emission intensity reduced significantly • CIII and OII emission intensity reduced. • MoI emission intensity didn’t change obviously • H/(H+D): ~90%40%

  19. 4.2 Comparison Li coating with boronization

  20. Summary • We have carried out Li coating successfully and good results were obtained in HT-7. • Li coating reduced impurity radiation significantly • By the Li coating, H/(H+D) can be controlled below 10%(Min. ~5%). • Li coating is useful for plasma recovery after vessel leak. • Lower particle recycling even if high fuel retention after Li coating; • The lifetime of 10-30g Li coating is about 60~100shots; • With Li coating contribution, various ICRF heating mode were easily achieved; • After 28 times Li coating, uniform and thick lithium film was found; • The boronization following 28 Li coatings also have good results.

  21. Thank you for your attention!! Acknowledgement 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

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