DEVELOPMENT OF MULTI-MEGA WATT NEGATIVE ION SOURCES AND ACCELERATORS FOR NEUTRAL BEAM INJECTORS

High energy and high power negative ion sources and accelerators have been developed for neutral beam (NB) injectors of future fusion machines such as International Thermonuclear Experimental Reactor (ITER). Using a 5-stage electrostatic accelerator, negative ion beam has been successfully accelerated up to the energy of 1 MeV, which is the required energy for ITER. Powerful negative ion beams of 18.5 A, 360 keV H- and 14.3 A, 380 keV D- have been produced with a high arc efficiency of 0.11 A/kW at a low source pressure of 0.15 Pa in JT-60 negative ion sources, and neutral beams of 5.2 MW have been injected into the plasma. Continuous operation of a Cs-seeded negative ion source has also been demonstrated for 140 hours, which is equivalent to the half year operation in the ITER-NB system