变像管相机中空间电荷效应的统计动力学分析

Statistical-dynamic analysis of space-charge effects in streak cameras

从Boltzmann积分微分方程出发推出了保守势场中电子数密度按势能的分布规律,即Boltz-mann统计分布。以此为基础,从统计动力学的角度详细分析了变像管相机中超短电子脉冲内部的空间电荷效应,通过求解Poisson方程得出了表征空间电荷效应的两个特征参量:空间电荷密度分布函数和速度分布函数,并对其按电位的动态变化规律进行了定性讨论。结果表明,限制变像管中的低电位区域和其中光电子脉冲从高电位向低电位传输的区域都将有助于优化整个变像管的性能。同时也重新讨论了光电阴极附近强加速场对光电子脉冲时间弥散的抑制作用,最终确定了其物理机制为不等位区间中电子脉冲空间分布的高度集中性。

Based on Boltzmann distribution law which is the derived distribution characteristic of electrons by potential energy in a conservative field from Boltzmann integrally differential equation in equilibrium state, the distribution functions of volume charge density and the velocity of electron pulse system in the externally supported unequal-potential space are achieved from the perspective of statistical physics by solving Poisson＇s equation. And the qualitative analysis of the dynamic variation characteris- tics of the two parametric distributions indicates that a higher external potential will restrain the unwelcome space charge effects which cause electron pulse broadening and energy spread. The physical mechanism of the optimization effect of higher electric field in the vicinity of the photocathode on the temporal resolution is proved to be the enhanced concentration of electrons in a streak camera, and it is not the well-recognized reduction of photoelectron energy spread. What＇s more, an inferential conclusion is also available that limiting the extent of the regions where the photoelectron pulse moves along the electric field will greatly improve the functional performance of streak cameras.