Life test studies on MM-cathodes

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°C _B and 1200°C_B (brightness). One group of cathodes was operated at constant anode voltage with an initial current density of 0.75 A/cm², and the other group was operated with a loading of 2 A/cm² for as long as the anode voltage could be adjusted. The cathodes at lower temperatures (⩽1100°C_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