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在托卡马克放电的初始阶段,由于存在变化的等离子体电流,一般会出现等离子体电流的趋肤分布,这种分布会导致MHD不稳定性的发展和产生破裂。早期的托卡马克实验,对放电初始阶段的MHD扰动现象做过许多讨论和研究。A1cator-A在电流上升段观测到的大多数破裂发生在q_L=1.6模处,同时观察到MHD扰动模式随时间从高模向低模的发展。电流初始阶段的上升率对平顶段的放电特性也有重大影响,在FT上,只有在等离子体电流上升率为1.2—2.6MA.s~(-1)时,才能实现低q_L的等离子体参数运行。
In the initial stage of tokamak discharge, there is generally a skin-like distribution of plasma current due to the varying plasma current, which leads to the development of MHD instability and to rupture. In the early Tokamak experiments, there were many discussions and studies on the MHD disturbances in the initial stage of discharge. Most of the cracks observed by A1cator-A at the current rise segment occurred at q_L = 1.6 and the evolution of the MHD perturbation pattern over time from high to low was observed. The rate of rise in the initial stage of the current also has a significant effect on the discharge characteristics of the flat top section. On the FT, the plasma parameters with low q_L can be achieved only when the rate of plasma current rise is 1.2-2.6MA.s ~ (-1) run.