KENBIKYO Vol.53▶No.1 2018

Electron Source Technology 2—vacuum and optics designs—

Keigo Kasuya and Shin Fujita

Abstract: Based on the first lecture on ‘Electron sources and guns 1,’ which discussed the optical/physical properties of electron sources, this second article deals with two fundamental designing technologies of electron guns. The one is the vacuum technology. The operation principles of cold field emitters (CFEs) are described from the viewpoint of vacuum science. The advantages of extremely high vacuum (EHV) over conventional ultra high vacuum (UHV) are explained in terms of the probe current stability and the high current capability. The second is the optical designing technique to achieve a high probe current. The point cathode optics require the consideration of ‘electron gun aberrations’ since its virtual source is very small and the angular current intensity low. The introduction of an optical parameter ‘electron gun focal length’ enables quantitative evaluation of gun aberration influences and the optimization of lens operation conditions.

Key words: cold field emitter (CFE) electron gun, extremely high vacuum, emittance diagram, optimum beam convergence angle