A Conceptual design and advanced R&D program for DEMO NBI

Inoue, Takashi

A fusion DEMO reactor requires NBI of high energy ( 1 MeV) for high power plasma heating and current drive. The NBI system for DEMO must fulfill other requirements such as (1) cw operation for 1 year, (2) low maintenance frequency ( once per year), (3) operability under radiation, (4) high system efficiency ( 50%). The present talk discusses DEMO NBI as a reasonable extrapolation of results from R&D and engineering design of the ITER NBI. For (1) and (2) above, R&D of filamentless source such as RF driven negative ion sources is in progress. The ITER R&D suggests possible extrapolation of exsisting electrostatic accelerator technologies up to 1.5 MeV. Additional radiation shielding is to be installed around the beam path, of which cross sectional area is reduced by merging multibeamlets into several beam groups. A concept of laser neutralizer, that utilizes semmiconductor lasers, is presented and discussed to achieve higher system efficiency close to 90%.