Analysis of traveling wave tube materials

A wide variety of materials are utilized in the construction of traveling wave tubes (TWT) used as microwave amplification elements for many Air Force applications. The only active component is the cathode which is heated to thermionic temperatures to serve as the electron emitting element in the electron gun section of the tube. Considerable interest exists in the correct scientific model of an activated cathode. Most such cathodes are barium-based and this research program has shown that barium in the metallic state is necessary on the surface of dispenser cathodes in order to get an acceptably low (< or = 1eV) work function. Other TWT materials investigated in this program include an evaluation of the electron bombardment resistance of boron nitride insulators and the determination of the activation mechanism and characteristics of nonevaporable zirconium-graphite getters. Other failure analysis investigations of TWT's are also reported herein.