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Presented by Y.J.Chen Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China

Workshop of 2011 Spring Experiment on HT-7. Investigation on Z eff and impurities behavior with molybdenum limiter in lithium coating experiments on HT-7 tokamak. Presented by Y.J.Chen Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China 2011.7.19. 1. Outline.

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Presented by Y.J.Chen Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China

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  1. Workshop of 2011 Spring Experiment on HT-7 Investigation on Zeff and impurities behavior with molybdenum limiter in lithium coating experiments on HT-7 tokamak Presented by Y.J.Chen Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China 2011.7.19 1

  2. Outline • Introduction • -- Significance of Zeffand impurity control • -- International development • -- The principle of Zefffrom V.B. and Define of averaged Zeff • Experimental Set-Up and major spectroscopy diagnostics • Lithium coating wall conditioning Experiment • Zeffand major impurities with lithium coating • Further more benefits for lithium coating • -- Lower particle recycling • -- Lower ratio of H/H+D • Conclusion and Discussion 2

  3. Introduction • For magnetically confined plasmas, How to control of impurity level is a critical issue for the fusion reaction in the future. the Z_effective is a significant parameter with indication of the total impurity level. Visible bremsstrahlung measurement is a powerful tool approaching to derive this key data. • Determination Zeff via Bremsstrahlung was first applied by Kadota on JIPP T-II in 1980, and soon used worldwide on many devices，such as DIII-D, JET, FTU,ASDEXUpgrade, LHD etc, for the regardlessness of the number of impurity species in the plasma. The best region to measure the radiation is in the visible. 3

  4. The Definition of an averaged Zeff Statistics Quantum Mechanics 4

  5. The principle of Zeff from V.B. The emission coefficient of bremsstrahlung radiation Zeff can be expressed as: and the line averaged Zeff is defined as: 5

  6. Outline • Introduction • -- Significance of Zeffand impurity control • -- International development • -- The principle of Zefffrom V.B. and Define of averaged Zeff • Experimental Set-Up and key spectroscopy diagnostics • Lithium coating wall conditioning Experiment • Zeffand major impurities with lithium coating • Further more benefits for lithium coating • -- Lower particle recycling • -- Lower ratio of H/H+D • Conclusion and Discussion 6

  7. Experimental Set-up • The HT-7 superconducting tokamak has a major radius of R=1.22m and a minor radius of a =0.27m in the circular cross-section. From this spring the graphite limiters had been instead of molybdenum limiters in order to develop the lithium wall conditioning experiments • Basically, the HT-7 tokamak with the limiter configuration is normally operated under the basic parameters: Ip=100-250kA, the toroidal magnetic field Bt=2T, the central line-averaged plasma density ne=0.5-6e19m-3 , central electron temperature Te=0.5-3.0keV and central ion temperature Ti =0.2-1.5keV 7

  8. Key spectroscopy diagnostics 1 Two 35-channel Da (λ = 656.1 nm) array2 The 6-channel Visible Bremsstrahlung emission 3 The fiber optic spectrometer 4 The 9-channel CIII (λ = 464.7 nm) array 5 Single channel impurity emission: OII (λ= 441.5 nm), OV (λ = 278.1 nm), MoI (λ = 386.4 nm) and LiI (λ = 670.8 nm). 8

  9. Outline • Introduction • -- Significance of Zeffand impurity control • --international development • --The principle of Zefffrom V.B. and Define of averaged Zeff • Experimental Set-Up and key spectroscopy diagnostics • Lithium coating wall conditioning Experiment • Zeff and major impurities with lithium coating • Further more benefits for lithium coating • --lower particle recycling • --lower ratio of H/H+D • Conclusion and Discussion 9

  10. Typical experiment of lithium coating #113140 before lithium coating, #113191 after lithium coating 10

  11. Outline • Introduction • -- Significance of Zeff and impurity control • --international development • --The principle of Zeff from V.B. and Define of averaged Zeff • Experimental Set-Up and key spectroscopy diagnostics • Lithium coating wall conditioning Experiment • Zeff and major impurities withlithium coating • Further more benefits for lithium coating • --lower particle recycling • --lower ratio of H/H+D • Conclusion and Discussion 11

  12. Zeff and major impurities with lithium coating 12

  13. The impurity amount varies with ne After lithiation After boronization boronization is further more effective to decrease the level of impurity 13

  14. Outline • Introduction • -- Significance of Zeff and impurity control • -- International development • -- The principle of Zefffrom V.B. and Define of averaged Zeff • Experimental Set-Up and key spectroscopy diagnostics • Lithium coating wall conditioning Experiment • Zeffand major impurities with lithium coating • Further more benefits for lithium coating • -- Lower particle recycling • -- Lower ratio of H/H+D • Conclusion and Discussion 14

  15. Further more benefits for lithium coating Red --after boronization Blue -- after lithium coating In despite of much more reduced Zeffafter boronization, lithium coating can get a very lower recycling of hydrogen and isotopes in the plasma edge and can get much more lower ratio of H/H+D after many times operation. The value of H/H+D can be decreased below 10%. It is benefit for ICRF minority ion heating 15

  16. Outline • Introduction • -- Significance of Zeff and impurity control • --international development • --The principle of Zeff from V.B. and Define of averaged Zeff • Experimental Set-Up and key spectroscopy diagnostics • Lithium coating wall conditioning Experiment • Zeff and major impurities with lithium coating • Further more benefits for lithium coating • --lower particle recycling • --lower ratio of H/H+D • Conclusion and Discussion 16

  17. Conclusion • Impurities and Zeff are reduced obviously by lithium coating wall conditioning • It is indicated by statistics that reduced impurities and Zeffseems inverse proportional to the quantity of lithium coating • The impurity amount varies approximately linearly with ne, which is useful for Zeff determination and also indicated that boronization is further more effective to decrease the level of impurity • In despite of much more reduced Zeffafter boronization, lithium coating can get a very lower recycling of hydrogen and isotopes in the plasma edge and can get much more lower ratio of H/H+D after many times operation. The value of H/H+D can be decreased below 10%. It is benefit for ICRF minority ion heating 17

  18. Discussion • Why does the Zeff much more larger with the molybdenum limiter than with the graphite limiter? It comes into being from higher Z molybdenum PFC and limiter configuration in lower density region(1-3e19m-3) on HT-7 • We are looking forward to doing the analysis of Zeff and impurities behavior on EAST with molybdenum PFC in lithium coating wall conditioning experiments in near future 18

  19. Workshop of 2011 Spring Experiment on HT-7 Thank you ! 20

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