The “virtual cathode” structure formed by the space charge near a thermionic emission cathode has a great influence on the characteristics of the emissive probe. The relationship between the characteristics of the virtual cathode in a vacuum and the probe filament temperature is not clear. Considering the initial velocity of the thermal electrons, we have derived an analytical expression of the virtual cathode potential. Combined with the experimental data, the dependence of the virtual cathode characteristics on the filament temperature of the emissive probe is obtained. The results show that the depth and the space scale of the virtual cathode increase almost linearly with the increase of the filament temperature. Additionally, a 1-D electrostatic particle-in-cell code is used to simulate the temporal evolution of the virtual cathode in a vacuum. The numerical simulation results are in good agreement with the theoretical calculation results.

热电子发射阴极附近空间电荷形成的“虚拟阴极”结构对发射探针的特性影响很大。真空中虚拟阴极的特性与探针灯丝温度之间的关系尚不清楚。考虑到热电子的初始速度，我们推导出了虚拟阴极电位的解析表达式。结合实验数据，得到了虚拟阴极特性对发射探头灯丝温度的依赖性。结果表明，随着灯丝温度的升高，虚拟阴极的深度和空间尺度几乎呈线性增加。此外，一维静电粒子单元代码用于模拟真空中虚拟阴极的时间演变。