Runaway plateau formation in EAST disruptions triggered by massive gases injection
T. Tang, L. Zeng, D. Chen, S. Lin, H. Zhuang, S. Zhao, H. Zhao, A. Ti, B. Zhang, Y. Sun, Y. Duan, L. Xu, H. Liu, R. Zhou, B. Gao, G. Zhong, J. Qian, C. Luo, Y. Jie, W. Xia, X. Zhu, Y. Liang, X. Gao, G. LiRunaway-electron (RE) plateaus have been observed during disruptions in experimental advanced superconducting tokamak (EAST) plasmas following the massive injection of argon into low-density ohmic discharges, which are performed with a circular plasma configuration under full-metal wall conditions. RE plateaus can maximally carry a current of 270 kA and last up to 400 ms. The formation of RE plateaus strongly depends on lower pre-disruption electron densities (0.2–0.5 × 1019 m−3) and a lower amount of argon injection (400–1000 Pa l), which correspond to an enhanced pre-disruption RE population and a reduced post-disruption electron density, respectively. Pre-disruption REs were found to survive the thermal quench, serving as extra seeds for the RE plateau. In addition, magnetohydrodynamic activity during the thermal quench was found to cause significant RE loss and affect RE plateau formation; in particular, the m/n = 3/1 and m/n = 2/1 modes were observed in sequence, leading to distinct RE loss patterns. Simulations on RE generation by a 0D model further confirmed the key roles of RE seeds to form an RE plateau in EAST.