The Technology of Neutral Beam Injection Based on Positive Ion Sources

Injection of energetic neutrals of hydrogen and deuterium has been used effectively to heat plasma in several fusion experiments. All applications to date have used neutral beams with pulse lengths in the subsecond range. The injected power extends into the megawatt level, approaching 10 MW in the case of PDX and D-III, with beam energies in the range of 20 to 80 keV. Key tokamak experiments are planned in which neutral beam injection will be applied at power levels extending toward the 25-MW range. A major difference in the injectors being planned for the future from those operating today lies in their need for longer pulse lengths. Extending the pulse lengths at higher power levels and a high beam brightness is the major goal of the neutral beam development laboratories. Other development areas include improving the atomic fraction in the beam to nearly 100%, increasing the beam brightness, and reducing the impurity content in the beam. Lifetime and reliability are also important considerations. This paper summarizes the advances made in each of these areas and elaborates on the work at Oak Ridge National Laboratory. Neutral injection parameters for a variety of fusion devices are also presented.