Long-pulse production of the negative ion beams for JT-60SA

Toward long-pulse productions of 22 A negative ion beams for 100 s in JT-60SA, the plasma generator of the negative ion source has been developed to achieve stable long-pulse generations of spatially uniform negative ions. To realize the long pulse production of the negative ions, an actively cooled plasma grid (PG) has been designed to keep a surface temperature of 250–300 °C optimized for high negative ion production. The designed active cooling system has a potential to control the surface temperature of the PG to 250 °C with a time constant of 10 s by flowing the fluorinated fluid having the high boiling temperature of 270 °C. Since the time constant is sufficiently shorter than that of the degradation of the negative ion production, the active cooling system is applicable to the long-pulse operation of the large-current negative ion source, such as JT-60SA and ITER ion sources. As for the high current beam production, spatial uniformity of the negative ion productions in the plasma generator is improved. The calculation results of the magnetically confined electron orbits emitted from filaments showed that longitudinal deviations of the primary electron distributions has been reduced from 27% to 6% by the application of the symmetric magnet arrangements, so called the tent-shaped filter. This reduction of the deviation could reduce the grid heat load, leading to the long pulse production of the negative ion beams.