The design and performance of high-current-density electron guns

Abstract

Electron guns used in power amplifiers and medium-and low-power klystrons are briefly discussed, and conditions for experimental guns are described. A useful figure of merit for a gun is obtained by biasing the focus electrode and normalizing the beam current at any bias voltage with respect to its unbiased value. These results, used with transmission against bias, provide a normalized efficiency which helps to evaluate design changes and tube-to-tube variations. Results on a h.v. reflex klystron gun illustrate performance at one micro-perveance-unit. Anode transmission is improved by using a cylindrical anode. The beam waist generally lies closer to the anode than predicted. A gun designed for a l.v. two-resonator klystron illustrates its behaviour at 4?5 micro-perveance-units. Transmission through a cylinder as a function of cylinder dimensions and perveance indicates severe anode divergence and a large beam-waist. Illustrations are given of some beam profiles from which a general beam-spread curve. For special conditions the anode becomes a tapered hole to shape the beam profile and thus make the convergence and beam angles approximately equal.