The operational phase of negative ion beam systems on JT-60U and LHD

This paper reviews the operational phase of the negative-ion-based neutral beam systems on the JT-60U tokamak in Naka, Japan and the large helical device (LHD) stellarator in Toki, Japan. These systems were the first high power negative ion beam systems to be deployed for any application, and thus represented large advances in the state of the art for negative ion sources and accelerators, especially since the ions used were hydrogen and deuterium, which have only a modest electron affinity. This paper reviews the systems, the principal problems encountered, and the improvements they engendered, as well as the progress of these systems to the present time. The role of neutral beams in fusion is also discussed, and some of the contributions of the negative ion systems to the physics programs of JT-60U and LHD are briefly reviewed. These systems have been central to the success of JT-60U and LHD, and the knowledge gained about their characteristics should provide a strong basis for the development of the next generation of negative-ion-based neutral beams for ITER and other large fusion devices.