Gas heating in the neutralizer of the ITER neutral beam injection systems

Indirect heating of the neutralizer gas by the beam has been shown to be responsible for the reduced neutralization efficiency observed in positive ion neutral beam systems. The translational gas temperature can be predicted from the neutralizer plasma density and electron temperature and, in general, a higher gas temperature implies a lower neutralization target. A simple one-dimensional model, originally developed for the JET positive ion neutral injection system, has been adapted for ITER relevant negative ion systems. The results imply that gas heating for the ITER heating and diagnostic beams is unlikely to be severe and hence the neutralization target might be expected to be close to the design value.