density modulation experiment within lithium coating on ht-7 tokamak

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Density Modulation Experiment within

Lithium coating on HT-7 Tokamak

Wei Liao ,Yinxian Jie, Xiang Gao and the HT-7 team

Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China

2011.7.19

HT-7tokamak 2011 data meeting and workshop 1

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Introduction

Experimental Set-Up

Density Modulation Experiment

– Modification principle and the major diagnostics– The calculation of transport coefficients: diffusion

coefficient (D) and convection velocity (V) Conclusion and Discussion

Outline

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Introduction

For magnetically confined plasmas, the study of the particle transport coefficients is a significant and perplexed issue in this field. Density modulation is a powerful approaching to solve the experiment difficulties.

For further particle transport research , this new density measurement is under the full metallic wall condition and lithium limiter applying.

Prompted lithium coating3

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Introduction

According the modulation principle, we can obtain the results which conclude particle transport coefficients under new conditions this year.

The most significant things is to make a comparison between the results this year and the ones under carbon wall and carbon limiter conditions in 2004

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Introduction

Experimental Set-Up


– Modification principle and the major diagnostics parameters

– The calculation of transport coefficients: diffusion coefficient (D) and convection velocity (V)

Conclusion and Discussion

Outline

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Experimental Set-up

Rebuilt from the original Russian T-7 tokamak in 1994, 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.

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 ,central electron temperature Te=0.5-3.0keV and central ion temperature Ti =0.2-1.5keV.

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Experimental Set-up

We may see that the main limiter stuffing equipment below:

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Introduction

Experimental Set-Up




Outline

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Density modulation experiment

The principle of density modulation:

The particle balance equation is shown as follows,

1 (1), n S r St r r

(2) nD Vnr

where n, Γ, S, D and V are electron density, particle flux, particle source rate, particle diffusion coefficient and convection velocity, respectively. Here, we assume the equilibrium and modulated components are independent, and separate these two components as follows,

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Then, the following particle balance equations for modulated components are obtained from eq.(1)

(3) ~SS ,~ ,~eq Snnn eqeq

(4) ~~ ,~~ , ~~ nitnenneSS titi

(5) 0~

~~1~11~2

2

DSn

Din

rV

DrDV

rn

DV

rD

Drrn

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Convection velocity is assumed to be zero at plasma center and increase proportionally to minor radius. This is expressed by the following equation.

V(r) = (r/a)V0

The value of D and V0 are scanned. For each D and V0 are calculated. Then, the difference between the experiment and calculated values is calculated to minimize as the following equation:

chord

IcalcIRcalcxp NLNLNLNL 2exp

2Re

2 )()(

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The major diagnostics and FIR detector:

Schematic of optical arrangement of Multi-channel interferometer

Waveguide Detector sensitivity ~100mV/mW

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IP=130kA, Bt=3800A, density measured by FIR interferometer system

Low density --1.5x1019 m-3 High density --2.2x1019 m-3


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The estimation of particle source by IDL program


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The calculation of transport coefficients: diffusion coefficient (D) and convection velocity (V) (two shots: under different density)

Low density - shot 112671 High density - shot 11283815

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The calculation of transport coefficients: diffusion coefficient (D) and convection velocity (V) (two shots: under different density)

Shot <ne> ( x1019 m-3)

D (m2/sec) V0 (m/sec)

112671 1.5 0.47 -2.5

112838 2.2 0.21 -3.6

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Introduction

Experimental Set-Up




Outline

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The Comparison

shot <ne>(x1019 m-3) D (m2/sec) V0 (m/sec)

67938 1.5 0.42 4.7

67941 2.2 0.28 -0.4

shot <ne>(x1019 m-3) D (m2/sec) V0 (m/sec)

112671 1.5 0.47 - 2.5

112838 2.2 0.21 -3.6

Experiment results without lithium coating in 2004

Experiment results with lithium coating in 2011

Point 1Point

1

Point 2

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The Discussion

when the background plasma density is 1.5x1019 m-3, the V in 2004 is positive ,but in the same background density the experiments operate under lithium coating circumstances in 2011, the V is negative, implying the desirable and expecting pinch effect

Of equal importance, we can tell the evident difference between the data V in 2004 and the data V in 2011 in higher density case (<ne> = 2.2x1019 m-3), since the absolute value of the later one is much larger than that of the former, inferring that the new experiments under lithium coating condition bring a better particle constraint.

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The Future work

the root reason why coating changes makes the significant difference deserves the further investigation and research.

more experiments with different modulation frequency, wall material and limiter will help us to get more sufficiently and effectively experiment data and to get more precise analysis

this technique is expected for the analysis of LHW and IBW heating in the future experiments on EAST tokamak.

Acknowledgement : This work was funded by the National Nature Science Foundation of China with contract NO.11075179.

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Thank you !

density modulation experiment within lithium coating on ht-7 tokamak

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