Concept of core and divertor plasma for fusion DEMO plant at JAERI

Fusion DEMO plant design at JAERI directs toward compactness and economy of the reactor with a fusion output at 3 GW level. The smaller size of the center solenoid (CS) has a large impact on reducing the reactor size and weight. Three candidates for CS, namely '-less', 'slim' and 'full' CS, are considered according to the role of CS coil that is plasma ramp up and plasma shaping. From points of views of technical feasibility, obtained triangularity (δ x) and weight of the reactor, the slim-CS is selected as the candidate for DEMO at JAERI. For slim-CS, high δ x (≥0.43), which is enough to suppress giant ELMs, is obtained, and highly radiative outer divertor is required in steady state power handling. The consistent equilibrium was found to satisfy the divertor requirements and radial build. During the plasma current ramp up phase, the acceleration voltage of neutral beam injection (NBI) has to be changed more than two times. In order to inject sufficient power during the low-energy beam injection, the present technology must be replaced by a new constant-current, variable-voltage technology