The results on high power injection with the neutral beam injection(NBI)systemfor the Large Helical Device(LHD)are reported.The system consists of three beam-lines withtwo hydrogen negative ion(H^- ion)sources installed in each beam-line.In order to improvethe injection power,a new beam accelerator with a multi-slot grounded grid(MSGG)has beendeveloped and applied to one beam-line.Using the accelerator,a maximum power of 5.7 MW wasachieved in 2003 and 2004,and the maximum energy of 189 keV was reached.The power andenergy exceeded the design values of the individual beam-line for LHD.The other beam-lines alsoincreased their injection power up to about 4 MW,and the total injection power of 13.1 MW wasachieved with three beam-lines in 2003.Although the accelerator had an advantage in high powerbeam injection,extracted beams expand in the short side direction of the ground-grid slot.Thedisadvantage has been resolved by modifying the aperture shapes of the steering grid.
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