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Oct 13 – 18, 2014
Hotel Park Inn Pribaltiyskaya
Europe/Moscow timezone

Dynamics of High-Intermediate-High Confinement Transitions on the HL-2A Tokamak

Oct 17, 2014, 8:30 AM
4h
Green 8-9 (Hotel Park Inn Pribaltiyskaya)

Green 8-9

Hotel Park Inn Pribaltiyskaya

Saint Petersburg, Russian Federation
Poster Poster 7

Speaker

Dr Jun Cheng (Southwestern Institute of Physics)

Description

It is essential to understand L-H transition mechanisms to provide a predictable power threshold for a successful operation in fusion reactors. Early theoretical and experimental studies have shown that plasma may pass an intermediate phase (I-phase) when the heating power gradually increases, approaching the H-mode power threshold. This extended time scale provides opportunity to study the L-H transition mechanism. Recently, this phenomenon accompanying with limit cycle oscillations was studied using a Langmiur probe array on the HL-2A in detail. Here, we report extended observations of dynamics in high-intermediate-high (H-I-H) confinement transitions on this device. The H-I transition was stimulated by the supersonic molecular beam injection (SMBI) with gas pressure2.5 MPa and pulse width2.0 ms. The Lissajous diagram between the normalized radial electric field X=e\rho_\theta|E_r|/T_e and the envelope of density fluctuations in the I-phase shows that all cycles rotate in the counterclockwise (CCW) direction, which means that the increase of the turbulence causes the reduction of radial electric field while the increase of the radial electric field induces decrease of turbulence. It seems that once the system enters such CCW LCO state the plasma may be able to enter a positive feedback loop which triggers the I-H transition. Another interesting finding is a coherent mode with 11.7 kHz appearing just prior to the I-H transition (lasting about 1.0 ms). The mode numbers of the magnetic fluctuations are identified to be m/n=3/1. It was found that the amplitude of magnetic fluctuations rapidly increases while that of LCOs significantly reduces. This contrast indicates that there is a possible interaction between the coherent mode and the turbulence, which is also favorable for the I-H transition. Detailed results will be presented.
Paper Number EX/P7-32
Country or International Organisation China

Primary author

Dr Jun Cheng (Southwestern Institute of Physics)

Co-authors

Prof. Beibing FENG (Southwestern Institute of Physics) Mr Chengyuan CHEN (Southwestern Institute of Physics) Dr Deliang Yu (Southwestern Institute of Physics) Prof. Jiaqi Dong (Southwestern Institute of Physics) Dr Kaijun Zhao (Sothwestern Institute of Physics) Prof. Kimitaka Itoh (NIFS) Prof. Lianghua YAO (Southwestern Institute of Physics) Mr Lin Nie (Southwestern Institute of Physics) Prof. Longwen YAN (Southwestern Institute of Physics) Prof. Qingwei YANG (Southwestern Institute of Physics) Prof. Sanae Itoh (Research Institute for Applied Mechanics, Kyushu University) Prof. Wenyu HONG (Southwestern Institute of Physics) Mr Wulu Zhong (Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People’s Republic of China) Prof. Xianming SONG (Southwestern Institute of Physics) Dr Xiaoquan JI (Southwestern Institute of Physics, Chengdu 610041 China) Prof. Xuantong Ding (Southwestern Institute of Physics) Prof. Xuru Duan (Southwestern Institute of Physics) Prof. Yong LIU (Southwestern Institute of Physics) Prof. Yuhong Xu (Southwestern Institute of Physics) Mr Zhihui HUANG (Southwestern Institute of Physics) Dr xiaolan zou (CEA)

Presentation materials