Technical design of NBI system for JT-60SA

Modification of JT-60U to a superconducting device (so called JT-60SA) has been planned to contribute to ITER and DEMO. The NBI system is required to inject D0 beams of 34MW for 100s. The upgraded NBI system for JT-60SA consists of 12 positive-ion-based NBI (P-NBI) units and one negative-ion-based NBI (N-NBI) unit. The injection powers of each P-NBI and N-NBI units are 2MW at 85keV and 10MW at 500keV, respectively. On JT-60U, the long pulse operations of 30s at 2MW and 20s at 3.2MW have been achieved on the P-NBI and N-NBI units, respectively. Both units have demonstrated no injection power degradation for long pulse operation. It has been also found that the thermal time constants of the main key components with active cooling, such as the ion source of the present NBI system, are less than ∼20s. Therefore, the pulse extension up to 100s is expected to need some modifications mainly the power supply system. In addition, the voltage-holding capability of the negative ion source is required to be improved. The detailed technical design of the NBI system for JT-60SA is presented.