阴极透镜层流电子枪调制特性

Modulating properties of electrostatic immersion objective laminar flow gun

通过求解第一类边界条件的拉普拉斯方程,获得了典型的三电极阴极透镜中轴上电位的解析表达式。以此为基础,分析了阴极透镜各几何参数及电位参数对其聚焦性能的影响,得知通过增大调制极电位或其孔径、增加调制极与加速极的间距或缩小调制极与阴极的间距的方法,可以保证在改善初始粒子时间、空间弥散特性的基础上,相对减小轴向电场的非均匀性以减弱其会聚电场强度,从而使带电粒子束在阴极透镜区域中不能形成交叠点,达到构成其中电子运动具有层流性质的阴极透镜层流电子枪的工程应用目的。另外也获得了采用厚度较小的调制极有助于整个电子光学系统性能优化的结论。

By solving Laplace＇s equation with the first class boundary condition, the analytical expression of the axial potential distribution in a typical triode immersion objective was achieved. Based on the related expression, effect of the geometrical parameters and potential ones on the focusing properties of the electrostatic lens is illustrated. The optained conclusions are that un-uniformity of the axial electric field directly results in the relatively weakened focusing field, together with the improvement of particles＇ temporal and spatial dispersion. The achieved modulating means are as follows： augment of the potential value and aperture size of the modulating electrode, increase of the intervals between modulating electrode and accelerating one, decrease of that of cathode and the former. With the traditionally formed crossover not existing in the region of objective, a new type of electron gun in which the charged particle can fly with the desired laminar flow characteristics can be developed accordingly. And also the specific result available in this paper is that thin modulating electrode is a better choice for the performance optimization of the whole electron-optical system.