Numerical Analysis of the Vertical Instability Stabilizing Effect of Saddle Coils in Tokamak

The stabilizing effect of tokamak plasma vertical position with saddle coils, which had been experimentally confirmed on the small tokamak PHiX, is evaluated numerically. The growth rate of the vertical position instability was evaluated by the three-dimensional linearized ideal MHD stability analysis code TERPSICHORE. The results of the evaluation showed that the growth rate decreased (increased) when the saddle coils were excited in the normal (inverted) direction, where the plasma vertical position had been stabilized (destabilized) in the experiments. It was also found that the growth rate was inversely proportional to the square of the saddle coils current, which was consistent with the tendency obtained experimentally. These results show that the TERPSICHORE code qualitatively reproduces the stabilizing effect of saddle coils.