Design and R&D for ITER NBI System at Jaeri

A 1 MeV, 50 MW Negative-ion-based Neutral Beam Injector (N-NBI) is proposed as a promising heating and current drive system for International Thermonuclear Experimental Reactor (ITER). The most crucial part of the ITER N-NBI is a negative ion source/accelerator, which is required to produce 1 MeV, 40 A D'ion beams for longer than 1000 s. The engineering design of the ion source/accelerator has progressed based on two major R&D at JAERI. One is the development of a high current negative ion source for the JT-60U N-NBI. After the demonstration of D'ion beam production of 400 keV, 13.5 A, the first neutral beam injection experiment has started from March 1996. The other is the development of a 1 MeV, 1 A accelerator which is composed of a five-stage, multi-aperture electrostatic acceleration system. The H*** ions have been successfully accelerated up to an energy of 805 keV, which is 80 % of the energy required for ITER. In addition to these R&Ds, design studies are carried out on the critical components of the ion source/accelerator. Among them, a method to control the temperature of the plasma grid by pressurized hot water is proposed to keep the negative ion production yield constant during the long pulse operation. For the durability under the high neutron environment, high purity alumina ceramics are adopted as insulator materials, and a new technology to fabricate a large insulator has been developed.