Assessment of possible high-energy neutral beam injection in DIII-D

The feasibility of injecting a high-energy neutral particle beam in the DIII-D tokamak is examined. From numerical calculations of beam deposition, beam losses, and current drive, it is concluded that neutral beam injection up to an energy of 300 to 500 keV is viable. The effect of multistep excitation processes on enhancing the ionization cross section of the energetic neutral particles is beneficial for such an experiment not only in terms of shirethrough reduction but also for mitigating prompt a bit losses of energetic ions. The knowledge obtained from such experiments would be essential for design, planning, and success for future large tokamak devices that will employ negative-ion based, high-energy neutral beam injectors