Density Modulation Experiment within Lithium coating on HT-7 Tokamak

1. Density Modulation Experiment within Lithium coating on HT-7 Tokamak Wei Liao ,YinxianJie, 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

2. Outline • 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 2

3. 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. 3 Prompted lithium coating

4. 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 4

5. Outline • Introduction • Experimental Set-Up • Density Modulation Experiment • Modification principle and the major diagnostics parameters • The calculation of transport coefficients: diffusion coefficient (D) and convection velocity (V) • Conclusion and Discussion 5

6. 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. 6

7. Experimental Set-up • We may see that the main limiter stuffing equipment below: 7

8. Outline • 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 8

9. Density modulation experiment • The principle of density modulation: • The particle balance equation is shown as follows, 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, 9

10. Density modulation experiment • Then, the following particle balance equations for modulated components are obtained from eq.(1) 10

11. Density modulation experiment 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: 11

12. Density modulation experiment • The major diagnostics and FIR detector: Schematic of optical arrangement of Multi-channel interferometer Waveguide Detector sensitivity ~100mV/mW 12

13. Density modulation experiment Low density --1.5x1019 m-3 High density --2.2x1019 m-3 IP=130kA, Bt=3800A, density measured by FIR interferometer system 13

14. Density modulation experiment The estimation of particle source by IDL program 14

15. Density modulation experiment • The calculation of transport coefficients:diffusion coefficient (D) and convection velocity (V) (two shots: under different density) High density - shot 112838 Low density - shot 112671 15

16. Density modulation experiment • The calculation of transport coefficients:diffusion coefficient (D) and convection velocity (V) (two shots: under different density) 16

17. Outline • 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 17

18. Conclusion and Discussion • The Comparison Point 1 Point 1 Experiment results without lithium coating in 2004 Point 2 Experiment results with lithium coating in 2011 18

19. Conclusion and Discussion • 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. 19

20. Conclusion and Discussion • 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. 20

21. Thank you !