Continuum-transition models of neutralizer gas heating

Indirect heating of neutralizer gas by the beam is believed to be responsible for the reduced neutralization efficiency encountered in positive ion neutral beam systems. This effect depends upon the details of gas flow within the neutralizer, which previous models have been unable to fully evaluate. Modeling this flow offers a significant challenge due to the gas flow regime encountered in such systems, and the numerous gas sources and sinks created by the neutralizer contents. Within the presented model, the Augmented Burnett Equations are used to simulate the continuum-transition gas flow within the neutralizer, with the development of detailed mass and energy sources and sinks to model a consistent gas-beam-plasma system. The 3-D model, originally developed for application to the JET positive neutral injection system, has been adapted for ITER relevant negative ion systems. The results suggest that the ITER neutralizer is subject to much reduced gas heating effects and no significant loss of neutralization target.