L-H power threshold studies with tungsten/carbon divertor on the EAST tokamak

L. Chen, G. S. Xu, W. Gao, L. Zhang, Anders Henry Nielsen, Z. P. Luo, H. Si, Y. M. Wang, H. Qu, Z. Sun, Y. M. Duan, H. Q. Liu, S. X. Wang, M. H. Li, X. J. Zhang, B. Wu, R. Chen, L. Wang, H. Q. Wang, S. Y. DingN. Yan, S. C. Liu, L. M. Shao, W. Zhang, G. H. Hu, J. Li, Y. L. Li, X. Q. Wu, N. Zhao, M. N. Jia

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Abstract

The power threshold for low (L) to high (H) confinement mode transition achieved by radio-frequency heating and molybdenum first wall with lithium coating has been experimentally investigated on the EAST tokamak for two sets of divertor geometries and materials: tungsten/carbon divertor and full carbon divertor. For both sets of divertors, the power threshold was found to decrease with gradual accumulation of the lithium wall coating, suggesting the important role played by the low Z impurities and/or the edge neutral density on the L-H power threshold. When operating in the upper single null configuration, with the ion grad-B drift direction away from the primary X-point, a lower normalized power threshold is observed in EAST with the tungsten/carbon divertor, compared to the carbon divertor after intensive lithium wall coating. A newly installed cryopump increasing the pumping efficiency also plays an important part in the observed lower threshold. In addition, the H-mode in the Quasi-Snowflake divertor configuration has been obtained on EAST, exhibiting higher L-H power threshold compared to the lower single null configuration with similar IP/BT pairs.
Original languageEnglish
JournalRadiation Effects and Defects in Solids
Volume171
Issue number5-6
Pages (from-to)359-373
Number of pages15
ISSN1042-0150
DOIs
Publication statusPublished - 2016

Keywords

  • L–H transition
  • Power threshold
  • Divertor geometry
  • Neutral recycling
  • Magnetic configuration

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