HT-7
ASIPP
Investigation on Zeff and impurities behavior with molybdenum
limiter in lithium coating experiments on HT-7 tokamak
Presented by Y.J.ChenPresented by Y.J.Chen
Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, ChinaInstitute of Plasma Physics, Chinese Academy of Sciences, Hefei, China
2011.7.192011.7.19
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Workshop of 2011 Spring Experiment on HT-7
HT-7
ASIPP
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 major 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
Outline
2
HT-7
ASIPP
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,ASDEX Upgrade, 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.
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HT-7
ASIPP
The Definition of an averaged Zeff
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2
=i i
ieff
i ii
n ZZ
n Z
, 1
i ii
effi
i eff i ii
i ii i
ie
p ZZ
pZ p Z
n Zp and p
n
F̂F
Statistics
Quantum Mechanics
( )
( )
ii
i
p i AA
p i
HT-7
ASIPP
The principle of Zeff from V.B.
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The emission coefficient of bremsstrahlung radiation2
1/26
2 3 1/2 2
16 exp3 6
e i i ffff i
e e e
n n Z gdP e hcd c m T T
1/2 1/2 22
6 3 2
3( )16 6 exp /
eeff
e e ff e
TcZ re m n g hc T
Zeff can be expressed as:
and the line averaged Zeff is defined as:
1/22 2
6 32 1/2
)316 6
( ) ( )exp /
a
aeff a
e ffe e e
a
r drcZe m g
n r T r hc T dr
(
HT-7
ASIPP
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
Outline
6
HT-7
ASIPP
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
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HT-7
ASIPP
Key spectroscopy diagnostics
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1 Two 35-channel Da (λ = 656.1 nm) array2 The 6-channel Visible Bremsstrahlung emission3 The fiber optic spectrometer4 The 9-channel CIII (λ = 464.7 nm) array5 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).
HT-7
ASIPP
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
Outline
9
HT-7
ASIPP
Typical experiment of lithium coating
10#113140 before lithium coating, #113191 after lithium coating
HT-7
ASIPP
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
Outline
11
HT-7
ASIPP
Zeff and major impurities with lithium coating
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HT-7
ASIPP
The impurity amount varies with ne
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After lithiation After boronization
boronization is further more effective to decrease the level of impurity
HT-7
ASIPP
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
Outline
14
HT-7
ASIPP
Further more benefits for lithium coating
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In despite of much more reduced Zeff after 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
Red --after boronizationBlue -- after lithium coating
HT-7
ASIPP
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
Outline
16
HT-7
ASIPP
Conclusion
Impurities and Zeff are reduced obviously by lithium coating wall conditioningIt is indicated by statistics that reduced impurities and Zeff seems inverse proportional to the quantity of lithium coatingThe 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 impurityIn despite of much more reduced Zeff after 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
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HT-7
ASIPP
Discussion
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• 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
HT-7
ASIPP
Thank you !
Workshop of 2011 Spring Experiment on HT-7
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