The stability margin on EAST tokamak

The experimental advanced superconducting tokamak (EAST) is the first full superconducting tokamak with a D-shaped cross-sectional plasma presently in operation. Its poloidal coils are relatively far from the plasma due to the necessary thermal isolation from the superconducting magnets, which leads to relatively weaker coupling between plasma and poloidal field. This may cause more difficulties in controlling the vertical instability by using the poloidal coils. The measured growth rates of vertical stability are compared with theoretical calculations, based on a rigid plasma model. Poloidal beta and internal inductance are varied to investigate their effects on the stability margin by changing the values of parameters $\alpha _n$ and $\gamma _n$(Howl {\it et al} 1992 \wx{Phys. Fluids {\rm B}}{4} 1724), with plasma shape fixed to be a configuration with $k = 1.9$ and $\delta = 0.5$. A number of ways of studying the stability margin are investigated. Among them, changing the values of parameters $\kappa$ and $l_i$ is shown to be the most effective way to increase the stability margin. Finally, a guideline of stability margin $M_s (\kappa ,l_i ,A)$ to a new discharge scenario showing whether plasmas can be stabilized is also presented in this paper.