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

The Role of Edge Plasma Instabilities in Dynamical Evolution of Pedestal in 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 Wulu Zhong (Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People’s Republic of China)

Description

Pedestal behaviors play a key role in determining the global energy confinement of tokamak plasmas, and fusion reaction efficiency of burning plasmas. It is essential to understand the mechanism of the pedestal formation and evolution for optimizing plasma performance and improving accuracy of predictive models. Thus it is important experimentally to track the swift evolution of the pedestal parameters and underlying instabilities in the narrow and steep gradient region. In HL-2A, the characteristics of the edge plasma instabilities and their effects on the dynamical evolution of pedestal have been investigated. Firstly, quasi-coherent modes have been observed in density fluctuations. The dominant mode with frequencies in the range of (50-100) kHz appears during the ELM-free period prior to the first ELM. By analyzing the pedestal density gradient, we found that there is a threshold for the excitation of the mode. This mode can also be observed during inter-ELMs. Experimental results show that the modes are excited after the ELM crash and terminated before the onset of the next ELM. The radial wave-number of the mode is estimated from the data measured by two radially separated reflectometers. The wave-number spectrum shows that the mode is radially propagating inward. The toroidal mode number of the edge mode is n=7 deduced from Mirnov signals. The corresponding poloidal mode number is about m=21 according to the local safety factor. A statistic method is applied to evaluate the relationship between the amplitude of the pedestal mode and the pedestal electron density gradient during ELM cycle. The result indicates that the modes are excited at about 40% of normalized interval before the ELM onset. During and after the ELM event, the modes disappear. It seems that the presence of the modes is linked to a relatively larger density gradient. In addition, the results made by a gyrokinetic simulation show that a Kinetic Peeling Ballooning Mode (KPBM) is localized in pedestal region, which has similar features to our observation. Thus, the edge mode in HL-2A is very likely a KPBM mode, and which may play a significant role in determining the dynamics of a pedestal.
Paper Number EX/P7-23
Country or International Organisation China

Primary author

Dr Wulu Zhong (Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People’s Republic of China)

Co-authors

Dr Deliang Yu (Southwestern Institute of Physics) Prof. Jiaqi Dong (Southwestern Institute of Physics) Dr Jiaxian Li (Southwestern Institute of Physics) Mr Jun Cheng (Southwestern Institute of Physics) Dr Liming Yu (Southwestern Institute of Physics) Min Jiang (Southwestern Institute of Physics) Mr Min Xu (Southwestern Institute of Physics) Dr Wei Chen (Southwestern Institute of Physics, P.O. Box 432 Chengdu 610041, China) 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. Yi Liu (southwestern institute of physics) Ms Yuan Xu (Southwestern Institute of Physics) Dr Zhongbing Shi (Southwestern Institute of Physics) Dr jinming Gao (Southwestern Institute of Physics) Dr longwen Yan (Southwestern Institute of Physics) Dr qingwei Yang (Southwestern Institute of Physics) Dr xiaolan zou (CEA) Dr yan zhou (Southwestern Institute of Physics) Dr yong Liu (Southwestern Institute of Physics) Dr yuhong Xu (Southwestern Institude of Physics) Prof. zhetian liu (Southwestern Institute of Physics)

Presentation materials