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Investigation of LHCD at high density in HT-7

Investigation of LHCD at high density in HT-7. L. Zhang, B. J. Ding, M. H. Li, E. H. Kong, J. F. Shan, F. K. Liu and HT-7 team. Background and Motivation. Background Fisch’s current drive theory: CD efficiency depends on 1/ne.

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Investigation of LHCD at high density in HT-7

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  1. Investigation of LHCD at high density in HT-7 L. Zhang, B. J. Ding, M. H. Li, E. H. Kong, J. F. Shan, F. K. Liu and HT-7 team

  2. Background and Motivation • Background • Fisch’s current drive theory: CD efficiency depends on 1/ne. • Experiments: Current drive efficiency drops dramatically above the ‘density limit’. • Motivation • To study the density limit in HT-7 and the effects of lithium and boron coating • To improve the current drive efficiency at high density by optimizing the CD conditions.

  3. Possible mechanisms • Accessibility • Parametric decay Instabilities (PDI) • Scattering of the LH waves by density fluctuations

  4. Recent experimental results • C-Mod • Accessibility condition is not the key factor for explaining the decrease in the efficiency.

  5. Recent experimental results • The major power of the LHW deposited in the SOL as the density limit occurs.

  6. Recent experimental results Without considering the collisional damping Considering the collisional damping The collisional damping is the loss mechanism.

  7. Recent experimental results • Sensitivity to plasma topology • SNncrit~8×1019 m-3 • DNncrit~1×1020 m-3 • limited ne~1.6×1020 m-3keeps 1/netrend

  8. Recent experimental results Low Te at the edge 1.6e20 • FTU • Lithium coating , Te ~200 eV, r/a~0.8 Current drive was observed at densities required for reactors. High Te at the edge 1.7e20 1.9e20 Figure (a) the differences of HXR between low Te (without lithium coating) and high Te (with lithium coating) at the edge. Figure (b) radial profiles of the HXR level at high density with lithium coating. High electron temperature in the plasma periphery is a key factor to improve the LHCD at high density

  9. HXR at different parameters

  10. Results and analysis • HXR emission satisfies the 1/ne trend. • No clear density limit

  11. Results and analysis • No obvious difference in HXR between lithium and boron coating wall

  12. Results and analysis The same level of Te (25~35eV) at the edge. (a) (b) Fig.(a)Te profile at the edge with boron coating. Fig.(b)Te profile at the edge with lithium coating.Ip=80kA Provided by Zhao Hailin

  13. Conclusions • In the limited configuration with wall maintenance, CD efficiency satisfies the 1/ne trend as the density is less than 3.5×1019 m-3. • There is no obvious difference in CD between lithium and boron coating wall.

  14. Future work • More discharges are needed in EAST at different configurations, plasma currents and magnetic fields to investigate the current drive efficiency at a large density range.

  15. Thank you!

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