Update of thermionic cathode progress

An update of progress in programs for improving thermionic cathode devices is presented. Innovative changes in the M-type impregnated cathode, specifically, the MM, CMM, MMM and transition metal emitters designed to preserve the initial cathode surface, are discussed. Also considered are low-cost high-brightness cathodes for high-definition television (HDTV), CPD types developed in the US and scandate types in Europe and Japan. High-temperature, high-brightness cathodes (LaB/sub 6/ and transition metal carbides) for lithographic or other unique applications are also discussed. Consideration is given to low-work-function cathodes (e.g. scandate) which can deliver 1-2 A/cm/sup 2/ at a much lower temperature than conventional impregnated cathodes and are capable of delivering pulsed currents in the range of 100 A/cm/sup 2/.<>