MHD instability dynamics and turbulence enhancement towards the plasma disruption at the HL-2A tokamak
Yucai Li, M. Jiang, Yuhong Xu, Z.B. Shi, J.Q. Xu, Yi Liu, A.S. Liang, Z.C. Yang, J. Wen, Y. P. Zhang, X. Q. Wang, Yuchen Zhu, Hangyu Zhou, W. Li, Ying Luo, Xiaojia Su, HL-2A, X.R. Duan, X.T. Ding, J.Q. Dong, Q. W. Yang, L.W. Yan, Yi Liu, X. L. Zou, D. Q. Liu, W.M. Xuan, L. Y. Chen, Junfeng Rao, Xiaohui Song, W.C. Mao, Q. M. Wang, Z. Cao, B. Li, J.Y. Cao, G.J. Lei, J. H. Zhang, X. D. Li, S. J. Wang, A. D. Liu, Ming-Lu Bu, Yihang CHEN, W. Chen, J. Cheng, C.H. Cui, Z.Y. Cui, Z.C. Deng, Ye Dong, Baijie Feng, Q. D. Gao, Xiaxia Han, Weijiang Hong, Hangbo Hu, M. Huang, Y. H. Huang, Xia Ji, Zihan Kang, Tao Lan, Guanzhi LI, Haoyu Li, Qing Li, Q. Li, W. Li, Y. G. Li, Z. J. Li, Z. T. Liu, C. W. Luo, X. H. Mao, Yuan Pan, Junkun Peng, K. Shao, X. Y. Song, H.J. Sun, A.K. Wang, H. Wang, M. X. Wang, Yeyun Wang, Z. T. Wang, W. W. Xiao, Zhixiang Xiao, Yuan Xie, L.H. Yao, Lingzi Yao, D.L. Yu, B.S. Yuan, K.J. Zhao, Yinjie Zheng, G. W. Zhong, Chu Zhou, Jianliang Zhou, Y. Zhou, Jiangyv Yan, C. X. Yu, Changhao Pan, Yong Liu
Abstract
The evolutions of MHD instability behaviors and enhancement of both electrostatic and electromagnetic turbulence towards the plasma disruption have been clearly observed in the HL-2A plasmas. Two types of plasma disruptive discharges have been investigated for similar equilibrium parameters: one with a distinct stage of a small central temperature collapse ([Formula: see text] 5-10%) around 1 millisecond before the thermal quench (TQ), while the other without. For both types, the TQ phase is preceded by a rotating 2/1 tearing mode, and it is the development of the cold bubble from the inner region of the 2/1 island O-point along with its inward convection that causes the massive energy loss. In addition, the micro-scale turbulence, including magnetic fluctuations and density fluctuations, increases before the small collapse, and more significantly towards the TQ. Also, temperature fluctuations measured by electron cyclotron emission imaging enhances dramatically at the reconnection site and expand into the island when approaching the small collapse and TQ, and the expansion is more significant close to the TQ. The observed turbulence enhancement near the X-point cannot be fully interpreted by the linear stability analysis by GENE. Evidences suggest that nonlinear effects, such as the reduction of local [Formula: see text] shear and turbulence spreading, may play an important role in governing turbulence enhancement and expansion. These results imply that the turbulence and its interaction with the island facilitate the stochasticity of the magnetic flux and formation of the cold bubble, and hence, the plasma disruption.