THE ARIES-II AND ARIES-IV 2ND-STABILITY TOKAMAK REACTORS

The ARIES research program is a multi-institutional effort to develop several visions of tokamak reactors with enhanced economic, safety, and environmental features. Four ARIES visions are currently planned for the ARIES program. The ARIES-I design is a DT-burning reactor based on "modest" extrapolations from the present tokamak physics database and relies on either existing technology or technology for which trends are already in place, often in programs outside fusion. The ARIES-III study focuses on the potential of tokamaks to operate with D He-3 fuel system as an alternative to deuterium and tritium. Two major cost items in the ARIES-I reactor are those associated with the magnet system and the current-drive system and recirculating power. Theoretical studies of the second MHD stability regime has been on-going in order to increase the toroidal beta (reduce the magnet cost) as compared to the first-stability regime. Recent analyses indicate that because second MHD stable plasmas have a high poloidal beta, the bootstrap current is high and can exceed the equilibrium plasma current. Therefore, the ARIES-II/-IV activity, therefore, has focused on second-stability equilibria in which approximately 100% of plasma current is produced by the bootstrap current. These equilibria have only moderate toroidal beta (approximately 4% to 6%) but the current-drive power (and cost) is small. Parametric system studies have confirmed that by operating in the second-stability regime with the constraint of approximately 100% bootstrap current, the COE of ARIES-II and ARIES-IV designs are approximately 25% lower than that of ARIES-I. The ARIES-II and ARIES-IV designs have the same fusion plasma but different fusion-power-core designs. The ARIES-II reactor uses liquid lithium as the coolant and tritium breeder and vanadium alloy as the structural material in order to study the potential of low-activation metallic blankets. The ARIES-IV reactor uses helium as the coolant, a solid tritium-breeding material, and silicon carbide composite as the structural material in order to achieve the safety and environmental characteristic of fusion. In this paper we describe the trade-off leading to the optimum regime of operation for the ARIES-II and ARIES-IV second-stability reactors and review the engineering design of the fusion power cores.