Conceptual design of negative-ion based 500 keV 20 MW neutral beam injector

The conceptual design of 500 keV, 20 MW neutral beam injector is reported in the present document. This design utilizes a negative ion source to realize a efficient high power neutral beam injector, by taking advantage of the high neutralization efficiency of negative ions at high energy. In the present report, the conceptual design of the source plasma generator and the accelerating system is presented first. Three candidate systems are then examined, each with a different neutralizing cell. The system having a very long neutralizer was judged to be the most suitable to the reactor considered. It was designed in detail. The long neutralizer (30 m) has many advantages: 1) The ion source can be located far from the reactor, permitting a narrow injection tube and tangential injection angle; 2) Neutron shielding is easy because the solid angle of the beam line is very small; 3) Complex components are removed from the vicinity of the reactor. The simplicity of the beam line leads us to believe that the chances for its actualization as a reactor injector is very high. More efficient neutralizers, such as a plasma neutralizer or a laser cavity, will give more flexibility to this design and provide further advantages for this injector. The realization of this injector will require development work for the negative ion source, the high voltage power supply, and the ion dump. When these components are developed, the rest of the system will be designed using previously developed positive-ion-beam technology. The present report is based upon notes from design meetings and broadly summarizes discussions, estimations and data those determined the parameters. (author)