Abstract
Mixed metal matrix cathodes (MM-cathodes) were optimized and their life behavior was tested in different test vehicles. In two separate life test programs, 57 MM-cathodes with a W/Os matrix were investigated in test vehicle (tetrodes) where the cathode environment was similar to that of a tube. In parallel, a further 100 MM-cathodes in other types of test vehicles were operated for supplementary investigations and cathode design optimization. The operational temperatures were between 880 degrees C/sub B/ and 1200 degrees C/sub B/ (brightness). One group of cathodes was operated at constant anode voltage with an initial current density of 0.75 A/cm/sup 2/, and the other group was operated with a loading of 2 A/cm/sup 2/ for as long as the anode voltage could be adjusted. The cathodes at lower temperatures (<or=1100 degrees C/sub B/) have accumulated more than 40000 h of operation. The results are used to establish cathode life prediction models as a function of temperature and current density. The excellent capability of the cathode type for long-life space applications has been demonstrated.<<ETX>>
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