Research on gas target neutralization processes for negative ion beam

Neutral Beam Injection (NBI) is one of the most important heating methods in magnetic confinement fusion. It needs to convert high-energy charged particles into neutral particles as efficiently as possible, and gas neutralization is currently widely used due to its simplicity and maturity. The target gas density distribution is a critical parameter for gas neutralizers, which affects the neutralization efficiency and beam transmission. This paper focuses on the processes of negative ion beam neutralization, based on a coupled simulation model of gas density distribution and beam transmission. The influence of gas injection methods and neutralizer length on the evolution of beam components were analyzed in detail. The results indicate that by maintaining the gas target thickness at the optimal value, the gas injection methods significantly affect the distribution of target gas density and the symmetry of beam particles at the beam transmission section. Increasing the length of the neutralizer can significantly decrease the required gas inlet rate, which can further reduce the vacuum system load and re-ionization of beam particles in the vacuum chambers. The influence of beam divergence on the power load distribution and transmission efficiency were also analyzed, providing references for the design of gas neutralizers in NBI systems.