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Snake perturbations during pellet injection and LHCD in the HL-1M tokamak

2004; IOP Publishing; Volume: 46; Issue: 3 Linguagem: Inglês

10.1088/0741-3335/46/3/003

1361-6587

Yi Liu, Xiaoming Qiu, Yunbo Dong, Gangcheng Guo, Zhengui Xiao, Yunzhe Zhong, Zheng Yinjia, Bingzhong Fu, J.Q. Dong, Yong Liu, Wang Enyao,

Solar and Space Plasma Dynamics

Excitation of snake perturbations has been observed in the core region of pellet-fuelled HL-1M plasmas when the pellets cross the surface with a q value of 1. It is observed that the snake oscillations have an m = 1, n = 1 helicity with quite a long lifetime. A detailed comparison has been made between the locations of the q = 1 surface and the snake oscillation. Through measurements of the plasma q-profile by means of multi-exposures with a CCD camera during pellet ablation, and investigation of the pellet ablation process, possible mechanisms for the formation of the snake oscillation are discussed. In addition, a large, long-lived snake-like oscillation is frequently observed in lower-hybrid current driven (LHCD) discharge in which the sawtooth has been stabilized early in the discharge. There is evidence that such a perturbation is due to impurity accumulation during sawtooth-stabilization, and good performance with peaking profiles after LHCD is limited by magnetohydrodynamic instabilities including sawtooth and snake activities in HL-1M plasmas.