VERTICAL POSITIONAL INSTABILITY IN JT-60SU

JT-60SU has been designed as an experimental device to establish an in tegrated scientific basis of steady-state tokamak operation. The high elongation of plasma cross section is employed to keep the safety fact or at the plasma surface high for high current operation. The vertical instability becomes very dangerous for this high elongation configura tion, and, among other MHD instabilities, it must be avoided first to obtain stable steady-state operation. The vertical positional instabil ity of JT-60SU is investigated and it is shown that the growth rate of vertical instability can be reduced to 30-50 Hz, and stability margin call be increased to 0.5 for a standard steady-slate configuration of JT-60SU by adding the baffle plate close to the plasma surface. It is also shown that the triangularity has a stabilizing effect on the ver tical instability for the standard equilibrium configuration of JT-60S U, because the absolute decay index value becomes smaller for higher t riangularity. (C) 1998 Elsevier Science S.A. All rights reserved.