Improvement of beam performance in negative-ion based NBI system for JT-60U

Injection performance of the negative-ion based NBI system for JT-60U has greatly progressed by optimizing ion source parameters, correcting beamlet deflection and improving source plasma non-uniformity. The long pulse beam injection for 10 seconds was achieved at 355 keV, 2.6 MW with one ion source by improving the beam divergence. A high injection power of 6.2 MW was realized by increasing an acceleration current. These results gave a significant contribution to the development of the negative ion based NBI system for ITER, which requires a steady-state operation with high energy and high current beams. (author)