利用Geant4程序建立外源注入式、低气压气体开关物理模型, 通过模拟计算电子增益与极板间电场强度、电子增益与极板间隙距离的函数关系验证了模型的正确性。计算了气体种类、气体压强对电子增益的影响, 分析得到形成自持放电所需最小入射电子数, 计算结果表明：在相同的气压及电场条件下, 氮气的电子增益远大于氦气, 这与氦气的高电离能性质相吻合; 随气压增大, 电子增益呈非线性增长; 为实现自持放电, 外源注入电子数面密度为1×105~2×105 /cm2。

This paper presents the design of a new low-gas-pressure gas switch that uses an external particle source for generating the original ionized particles, using Geant4 program to build the physical model of the switch. Verification shows that the model is reliable and effective. The model is adopted to calculate the effect of gas species and gas pressure on electron gain, get the minimum injected-electron number for forming self-sustained discharge. The simulation results show that the electron gain of nitrogen is considerably larger than that of helium, which is in accordance with the higher ionization energy of helium. The electron gain increases with increasing gas pressure in the form of nonlinear growth. To form self-sustained discharge, the density of injected-electron is (1-2)×105/cm2.