Neutral beam injection heating is a very effective auxiliary heating method in magnetic confinement fusion experiment. The built 5 MW neutral beam injection plays an important role in the H-mode operation with 1 MA plasma current of HL-3 tokamak. In order to achieve the H-mode operation with 2.5 MA, three neutral beam injection heating systems will be constructed with a total heating power of 20 MW.

This study aims to investigate the transmission efficiency of 7 MW neutral beam injector designed for HL-3 tokamak.

The beam transmission efficiency was studied from two aspects of neutralization efficiency and power deposition. The initial target thickness of the neutralizer under two beam parameters was analyzed based on Monte Carlo method. The optimal neutralization efficiency was achieved by adding neutralizer gas supply, and the target thickness required for the optimal neutralization efficiency was given. Finally, power deposition method was employed to analyze the transmission performance of the two neutral beams with different parameters at different beam divergence angles.

The results show that the optimal neutralizer efficiency is achieved when the neutralizer gas supply is 0.6 Pa?m³?s^-1 and 1.1 Pa?m³?s^-1, respectively. The neutral beam power obtained under two beam parameters with a divergence angle of 1.2° is 7.2 MW and 6.8 MW, respectively, and the corresponding transmission efficiency is 0.4 and 0.35, respectively.

The new neutral beam injector of HL-3 tokamak will be built according to the design of this study, with optimized parameter of 100 kV/45 A, while still retaining the ability to deliver a 120 keV deuterium beam.