Life test studies on tungsten impregnated cathodes

NASA-Lewis Research Center has conducted an ongoing life test program on commercial impregnated tungsten cathodes since 1971. This brief is an update of the information as of December 1979. "B"-type cathodes, operated at 1100°C have been run in simulated microwave tubes at 2 A/cm
²
for more than four years with about 6- percent degradation in current at a constant reference anode voltage. "M'-type cathodes have been operated for 30 000 h at a cathode temperature of 1010°C and 2 A/cm
²
with no degradation in current at a constant reference anode voltage.