The CPC: A Medium Current Density, High Reliability Cathode

Modern requirements for high-power microwave tubes having very high reliability have accentuated the demand for cathodes capable of dc or long pulse emission in the range 0.5 to 1.0 amps/cm 2 over lifetimes up to 50,000 hours. The best oxide cathodes available function only at the lower end of this range over relatively short lifetimes, and in consequence metal matrix types are normally used. The most widely used of these is the tungsten matrix, but this demands operating temperatures of the order of 1000°C,* and the reliability of the tube then begins to depend on factors such as the integrity of the cathode heater and its radiation shielding. Nickel matrix cathodes, prepared from powder compacts of nickel and active oxides, and * T h r o u g h o u t the remainder of this paper, °C will be used to mean degrees Centigrade true temperature. T h e abbreviation °B will be used to mean degrees Centigrade brightness on nickel as measured by optical pyrometer on the side of the cathode button. 2375