Optimization of Steady-State and Hybrid Operations in a Tokamak Fusion Reactor by Using Divertor Scaling Models

Steady-state and hybrid-mode operation of a tokamak fusion reactor is investigated by power balance calculations, and operation points are optimized with respect to divertor heat load. The dependence of the divertor heat load on a variety of models is also discussed. Several schemes to reduce the heat load are investigated, and the goal of physics research and development is clarified. Hybrid-mode operation appears to be suitable for technology testing, which requires a long burn time and a high neutron wall load. The divertor heat load can be reduced to the ignition-mode level without impurity seeding if the energy confinement is enhanced by 10%. The relation between the divertor heat load and the controllability of the current profile, that is, the fraction of the beam-driven current, is also discussed.