Tungsten-Point-Cathode Electron Gun Using Electron Bombardment for Cathode Tip Heating: Cathode Life and Operating Characteristics at Cathode Temperatures above 2,800K

A new type of tungsten point cathode electron gun was operated at higher cathode temperatures (^ 2,800 K), and its cathode life and operating characteristics were examined. In this gun, a straightened tungsten wire is used as the cathode, and the tip is locally heated by a disk-shaped electron beam from a heater assembly set inside the Wehnelt cylinder. The electron beam heating confines the cathode evaporation to the tip part and improves the working life of the cathode at higher temperatures, or emission current densities. At 3,150 K, the gun provides a stable beam with the Langmuir's theoretical brightness, where the brightness is one order of magnitude higher than the conventional hairpin cathode gun. The cathode shapes after the gun operation, the measured evaporation rate of the cathode tip, and the estimated relation between the cathode life and the beam brightness are described. © 1996 Oxford University Press. All rights reserved.