Study on the L–H transition power threshold with RF heating and lithium-wall coating on EAST

Nuclear Fushion

article

L. Chen¹  G.S. Xu¹  A.H. Nielsen³  W. Gao¹  Y.M. Duan¹  H.Q. Liu¹  L. Wang¹  M.H. Li¹  M. Wang¹  X.J. Zhang¹  R. Chen¹  H.Q. Wang¹  Z. Sun¹  S.Y. Ding¹  N. Yan¹  S.C. Liu¹  L.M. Shao¹  W. Zhang¹  G.H. Hu¹  J. Li¹  L. Zhang¹  B.N. Wan¹  the EAST Team¹ 

[1] Institute of Plasma Physics, Chinese Academy of Sciences;University of Science and Technology of China;Department of Physics, Technical University of Denmark;School of Physics and Optoelectronic Technology, Dalian university of Technology

关键词: L–H transition;    power threshold;    divertor configuration;    lithium-wall coating;    wall material;   

DOI  :  10.1088/0029-5515/56/5/056013

来源: Institute of Physics Publishing Ltd.

【 摘 要 】

The power threshold for low (L) to high (H) confinement mode transition achieved by radio-frequency (RF) heating and lithium-wall coating is investigated experimentally on EAST for two sets of walls: an all carbon wall (C) and molybdenum chamber and a carbon divertor (Mo/C). For both sets of walls, a minimum power thresholdP _thr of ~0.6 MW was found when the EAST operates in a double null (DN) divertor configuration with intensive lithium-wall coating. When operating in upper single null (USN) or lower single null (LSN), the power threshold depends on the ion  ∇ Bdrift direction. The low density dependence of the L–H power threshold, namely an increase below a minimum density, was identified in the Mo/C wall for the first time. For the C wall only the single-step L–H transition with limited injection power is observed whereas also the so-called dithering L–H transition is observed in the Mo/C wall. The dithering behaves distinctively in a USN, DN and LSN configuration, suggesting the divertor pumping capability is an important ingredient in this transition since the internal cryopump is located underneath the lower divertor. Depending on the chosen divertor configuration, the power across the separatrixP _loss increases with neutral density near the lowerX -point in EAST with the Mo/C wall, consistent with previous results in the C wall (Xuet al2011Nucl. Fusion51072001). These findings suggest that the edge neutral density, the ion  ∇ Bdrift as well as the divertor pumping capability play important roles in the L–H power threshold and transition behaviour.

【 授权许可】

Unknown