Rigid body passive and active stability of ITER

Passive and active vertical stability properties of ITER (International Thermonuclear Experimental Reactor) are presented based on a linearized, rigid body model of plasma motion within a set of axisymmetric conducting elements. The proposed passive twin loops concept and a single, midplane symmetric coil pair are analyzed with emphasis on the active control problem. An ideal proportional/derivative controller is used to predict system performance for nominal and off-nominal plasma conditions. The proposed system is shown to meet the primary fast active control specifications for vertical control in ITER. Recommendations are made for improvements in performance based on active control coil position. The combined vacuum vessel and passive shell structure in ITER is shown to be sufficient to meet the design requirements for vertical passive stabilization and the power requirements for the active control system. The proposed system, operating with the baseline plasma, has a 105% margin against Alfven time scale growth and a growth rate of approximately 20 s^-1. The active control system can stabilize a 10-cm initial displacement for the nominal plasma and a 5-cm displacement for the deteriorated plasma within a 1-GVA power supply limit