Evaluation of operation scenario for fusion DEMO plant at JAEA — Constraint of neutral beam injection system

The ramp-up scenario of the plasma current (Ip) without the center solenoid (CS) coil in the case of a DEMO plant at JAEA is evaluated using the zero-dimensional system code. The scenario is estimated from low Ip (2 MA) to the final fusion reaction during the period of neutral beam injection (NBI). The beam energy (ENBI) of NBI is required to be changed using new constant current variable voltage (CCVV) technology more than two times during the plasma current ramp-up. The constraints of NBI power (PNBI) are evaluated from the plasma requirements and use of CCVV technology. Time evolutions of plasma parameters are evaluated using the circuit equation with zero-dimensional particle and power balance equations. The final state with a fusion output of 3 GW from low Ip (2 MA) can be reached by changing ENBI using CCVV technology. During the plasma current ramp-up phase, NBI power is needed to be larger (90 MW) than that in a flattop. It takes 2.5 h to reach the final state.