The electron gun:
The electron gun is the source of the electron stream. It used to create a fine beam of electrons of precisely controlled energy all coming from a small source region. There are two types of electron guns: the Thermionic electron gun and the Field emission gun.
The Gun which is used at the Tecnai F30 G² is a Shottky type Field Emission Gun. These Gun holds advantages in producing a coherent and very small in diameter electron beam. Also it is usable with a flexible high tension of 200 kV apart from the regular 300 kV.