Transitional modelling of the neutral gas in the JET neutraliser

Effective understanding of gas flow is important to ensure efficient operation of gas neutraliser systems such as that used at Joint European Torus (JET), which form part of neutral beam heating systems for nuclear fusion experiments. Offering a means of neutralising the charge of initially ionic beams, gas neutralisers permit the injection of beams of neutral particles into the tokamak vessel, which serve to both heat the plasma and drive plasma current. Within the JET neutraliser, gas flow encompasses both the continuum-transition and molecular flow regimes, encouraging the application of novel techniques. The first application of the Augmented Burnett Equations to these systems is presented with results compared to experimental pressure profile data. The results demonstrate that the application of the Augmented Burnett Equations is a valid modelling approach. The strong dependence of accuracy upon outlet Kn is noted and good agreement found with experiment as rarefaction approaches the molecular limit of Kn=1, beyond the theoretical domain of applicability.