Abstract: Electron Impact(EI) ion source is a core component for the miniaturized magnetic mass spectrometer, and its performance has a great impact on the mass resolution and sensitivity of the instrument. In this study, the structure of ion repeller electrode was optimized and the voltage driving method was improved to enhance the overall performance of the EI source. Three-dimensional model of the miniaturized EI source was constructed using the ion simulation software simion-8.0, and the simulation was focused on investigating the influence of geometric parameters, ion repeller shape and the electric parameters on the ion focusing performance and ion transfer efficiency. By simulating the trajectory of ions, the ion motion parameters were obtained. At the same time, the ion focusing effect and ion transfer efficiency of the EI source were analyzed using the phase space method. The theoretical simulation results show that the ion's position focusing radius was less than 0.08 mm and ion transfer efficiency of over 99% were achieved when S₁=1.2mm, S₂/S₁=1.6, S₃=2mm, ion repeller was arc shape and the ion focusing lens and the main slit were driven by the high voltage and constant voltage tracking method. The ion transfer efficiency and the ion focusing performance could be greatly improved when the ion repeller structure and the voltage driving method were improved. Furthermore, high ion focusing performance could be maintained during the whole mass range. The optimized EI source could greatly improve the sensitivity and mass resolution of miniaturized magnetic mass spectrometer. Although we only investigated the performance of geometric parameters and repeller structure and electric parameters by simulation, the achievements would be helpful and instructional for further experiments and study.

Key words: electron impact ion source, ion repeller electrode, constant voltage tracking, ion focusing performance, ion transfer efficiency