Passive vertical stability of ITER (International Thermonuclear Experimental Reactor)

Next generation tokamaks, such as the International Thermonuclear Experimental Reactor (ITER), are being designed with high plasma current carrying capability. High current is best achieved by increasing the plasma elongation; however, this leads to a plasma configuration which is unstable to axisymmetric vertical motion of the plasma. Passive conductors must be included in the design to stabilize this vertical motion. In this paper, the authors analyze the passive stability property of the Physics Phase (PP) operation of the ITER device. A linearized, rigid-body assumption is used to predict the stability parameter of the proposed passive stabilization structure. The problem is formulated into an eigenvalue problem and the solution predicts the critical stability margin and characteristic growth rate. The proposed stabilization structure and vacuum vessel (VV) provides 50% margin against Alfven time scale vertical motion. The growth rate is less than 50 s-1 for the nominal plasma. The plasma is shown to have low growth rates over a range of plasma internal inductance and poloidal beta. 3 refs., 5 figs., 5 tabs