High current density M-type cathodes for VEDs

The emission performance and life of most VEDs (vacuum electron devices) is directly related to the capability of cathode. As the main force of thermionic sources, dispenser cathodes made of a porous tungsten pellet impregnated with Ba, Ca aluminates, such as M type cathodes (coated with Osmium, Iridium or Osmium/Ruthenium) and scandate cathodes, play an important role in the electron beam devices. This paper presents some results obtained during the investigation of M-type cathodes used in TWTs (traveling wave tubes) and klystrons. The investigation covers the following experiments: (i) the lifetime test in close space diode to evaluate the long term life capability of M-type cathodes operated at different temperatures and loads to fulfill the missions for VEDs; (ii) the assessment of performances of M-type cathode delivery high current density up to 32A/cm² in standard Pierce electron gun; (iii) the application of M-type cathode in practical X-band dual mode TWTs and Ka, X band MBKs (multi beam klystrons); (iv) the investigation of high reliable "quasi ceramic" potted heaters that shorten the warm-up time significantly. The experimental approach such as cathode structures, test vehicles and experimental techniques are also demonstrated in this paper.