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High-Power and Long-Pulse Injection with Negative-Ion-Based
Neutral Beam Injectors in Large Helical Device
Abstract:
A negative-ion-based neutral beam injection (NBI) system has been operated reliably in the Large Helical
Device (LHD) since it was operational in 1998. The injection power achieved is 13.1 MW with three injectors.
In one injector with modified ion sources with the multi-slotted grounded grid, the injection power reached 5.7
MW with an energy of 184 keV, both of which exceed the designed values of 180 keV - 5 MW. The individual
control of the arc-discharge with the divided arc and filament power supplies is effective to improve the beam
uniformity. The injection duration is extended to 120 sec with a reduced power of 0.2 - 0.3 MW using one ion
source with the cooled plasma grid. The performance of the negative-NBI in LHD is reviewed with regard to the
progress of the negative ion sources.
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Synopsis (pdf)