Issues in Cathode Performance: Part 1 - Tip shape and Crystal Orientation

Abstract

Abstract LaB6 (and CeB6) cathodes are widely used as high-brightness cathodes in a variety of electron beam applications. These cathodes provide about 10 times the brightness and about 100 times the service life of a tungsten filament. However, to fully realize the improved brightness and lifetime of the LaB6 (CeB6) cathode, it must be designed and manufactured specifically for the application. This article covers tip shape and crystal orientation. Future articles will deal with materials selection, preparation, purity, composition, and cathode operation. The design of the LaB6 cathode tip is critical for maximum lifetime and optimum performance. The cathode must also provide the appropriate source size, beam current, and beam brightness for the application. The lifetime of the LaB6 cathode is limited by three basic factors: cathode temperature, vacuum pressure, and tip shape. The first two factors are critical and depend on proper user operation. Poor vacuum and excessive temperatures accelerate LaB6 material loss, which decreases the cathode lifetime. The third factor, tip shape, is also critical, and careful production control ensures that the tip shape is optimized.