Progress of negative ions in fusion research

Negative ion beams are assuming increasing significance in the field of controlled fusion research. The first generation of large high current negative ion sources has now operated successfully on the JT-60U tokamak for some years, producing negative ions of hydrogen or deuterium at energies up to 400 keV for conversion to several megawatts of neutrals which are used for plasma heating and current drive. We report an unexpected intensification phenomenon, and some of the improvements made or planned. In the realm of inertial confinement fusion, interest has grown in the use of heavy negative ion driver beams formed from halogens such as bromine, iodine, or chlorine. We discuss the advantages of negative ions as heavy ion fusion drivers, and assess the technical feasibility of a halogen negative beam system. We also discuss the potential for photodetaching the negative ions to produce atomically neutral beams and reduce beam space charge effects within the target chamber.