Theory of Electron Gun

The function of the electron gun irrespective of the purpose for which the cathode ray tube is used is to generate, to concentrate, to control, and to focus an electron beam to a spot of a desired size. This paper describes the theory of the above-mentioned functions. The point of view of electron optics is presented and the theory of thick electron lenses with variable indexes of refraction is given. A somewhat detailed analysis of the action of the various parts of the gun is given, using the concepts of electron optics whenever convenient. Then a relevant part of thermionic emission is treated, with an emphasis on the distribution of velocities of emission. The initial concentration in the proximity of the cathode, the control of the beam intensity, and the effects of space charge are presented next. In closing, the performance of the gun as a whole is given, and a mathematical and graphical design procedure, made possible by certain assumptions and approximations, is described.