Assessment of water-cooled breeder resistors for long pulse injection in acceleration power supply on positive-ion-based NBI system

Water-cooled breeder resistor, utilized in acceleration power supply on the positive-ion-based NBI system, has been designed to realize 100 s injections of intense neutral beams in JT-60 Super Advanced. The design is progressed with minimizing modification of existing electric parts. Existing water-cooled breeder resistors is composed of three water vessels connected in parallel, in each of which 150 resistors of 600 Ω are immersed and connected in series. Although the manufacturing company requires entire replacement of water- cooled breeder, the careful assessment of thermal load allows only the replacement of the resistors inside the water vessel. The resistance of one resistors is required to be increased from 600 Ω to 2.5 kΩ. The total resistance of the breeder is ∼140 kΩ that includes the resistance of water. In the operation with the breeder of ∼140 kΩ, stable production of 85 keV, 55 A D+ beams, allowing 2 MW of the designed injection power, was confirmed without instabilization of the acceleration power supply. This modification significantly reduces the cost and the manufacturing time. (author)