A versatile test rig for the evaluation of thermionic electron guns

Abstract

Measurements of the brightness and the electron energy distribution for high-performance electron guns for electron-optical instruments must take account of the small effective size of the electron source and the directional dependence of the emission from it. A versatile electron gun test rig has been developed to enable measurements to be made under realistic operating conditions. Energy distribution can be determined with a hemispherical cup retarding-field analyser, and brightness can be measured at up to 100 kV by both two-aperture and crossover-projection methods. Some measured characteristics of lanthanum hexaboride cathodes are given, with measurements of conventional tungsten cathodes for comparison.