Modeling the gas flow in the neutralizer of ITER neutral beam injector using Direct Simulation Monte Carlo approach

The neutralizer is a key element in the neutral beam injector, where the energetic ion beam converts to the needed neutral beam. Within the gas neutralizer, the gas flow pattern has a great influence on the neutralization efficiency of the ion beam and the gas load on the vacuum vessel. In most of the neutralizers currently used, the gas flow falls within the transitional and molecular flow regimes. Considered the Direct Simulation Monte Carlo (DSMC) method is a benchmarking in the simulation of transitional regime flow, it was firstly introduced to the gas neutralizers in this study. The simulation procedure has been described in detail and applied to the ITER neutralizer case for demonstration. The predictions are compared with existing results using Test Particle Monte Carlo (TPMC) method, and indicate the importance of molecular collisions. The results show that the distribution of gas flow is nearly linear in most region of the neutralizer, but there are some stagnation zones around the gas inlet.