Speaker
Prof.
Jiaqi Dong
(Southwestern Institute of Physics)
Description
Detailed analyses of the dynamic evolutions of the pedestal, including density, temperature, pressure and their gradients were performed in recent H-mode experiments on HL-2A tokamak. Dramatic increase of density gradient and decrease of electron temperature gradient were observed in the pedestal just prior to each burst in a series of ELM eruptions. An inward particle flux inducing quasi-coherent mode was found to be responsible for such changes, and triggering the ELM eruption. The results clearly show that the mode grows very rapidly 200 microseconds before each ELM burst in the H-mode plasma. The auto-power spectrum analysis indicates that the mode peaks at f=50-60 kHz. A higher harmonic at 120 kHz also appears in the density spectrum, but not in the floating potential. The poloidal and toroidal mode numbers are estimated as m20-24 and n=m/q6-8, respectively. The poloidal propagation velocity of the mode is estimated as 6.0-7.2 km/s at r=-10.0 mm. The radial wave vector of the mode is kr3.5-7.5 cm-1, propagating inward with a velocity of 400-850 m/s. The mode propagates in plasma current direction toroidally. The squared auto-bicoherence analyses of the floating potential and density fluctuations indicate that nonlinear three-wave coupling might be a plausible mechanism for the generation of the quasi-coherent mode. Decoupling of the mode induced density transport from energy transport, similar to that observed in I-mode discharges, was observed. A very interesting observation in the experiments is that the gradient scale length of electron density is always shorter than that of temperature at the starting point of the ELM burst and, therefore, the dominant role of density gradient over temperature gradient for ELM triggering is demonstrated. The results are consistent with I-mode discharges where high temperature gradient does not lead to ELM and in contrast with the previously reported quasi-coherent modes which play significant roles in sustaining H-mode discharges [1-3].
References:
[1] Yan Z. et al 2011 Phys. Rev. Lett. 107 055004
[2] Diallo A. et al 2014 Phys. Rev. Lett. 112 115001
[3] Wang H.Q. et al 2014 Phys. Rev. Lett. 112 185004
| Country or International Organization | China |
|---|---|
| Paper Number | EX/P7-24 |
Primary author
Prof.
Jiaqi Dong
(Southwestern Institute of Physics)
Co-authors
Dr
Deliang Yu
(Southwestern Institute of Physics)
Dr
Hongdz He
(Southwestern Institute of Physics)
Mr
Jianqiang Xu
(Southwestern Institute of Physics)
Dr
Jun CHENG
(Southwestern Institute of Physics)
Dr
Kaijun Zhao
(Sothwestern Institute of Physics)
Prof.
Kimitaka ITOH
(National Institute for Fusion Science)
Dr
Longwen Yan
(Southwestern Instotute of Physics)
Prof.
Qingwei Yang
(CnSWIP)
Prof.
Sanae Itoh
(Research Institute for Applied Mechanics, Kyushu University)
Dr
Shigeru Inagaki
(Kyushu University)
Dr
Wulyu Zhong
(CnSWIP)
Dr
Xiaoquan JI
(Southwestern Institute of Physics, Chengdu 610041 China)
Prof.
Xuantong Ding
(CnSWIP)
Prof.
Xuru Duan
(Southwestern Institute of Physics)
Dr
Yong Shen
(Southwestern Institute of Physics)
Mr
Yonggao Li
(Southwestern Institute of Physics)
Mr
Zhihui Huang
(Southwestern Institute of Physics)
Dr
Zhongbing Shi
(Southwestern Institute of Physics)
Dr
xiaolan zou
(CEA)
