Supply and loss mechanisms of Ba dispenser cathodes

Abstract Ba dispenser cathodes, especially W–I, Re–I, Os/Ru–I and Sc 2 O 3 /Re top-layer Scandate cathodes have been investigated with respect to Ba resupply, Ba evaporation and ion bombardment behaviour. Since a 411 impregnated base was used for all these types, the same Ba evaporation activation energy of 3.15 eV was found despite different surface coatings. These and further results are compared with literature data. From ion bombardment (=IB) investigations different sputter yields are derived. With respect to IB stress tests, dynamic shielding of the surface complex rest by Ba sitting on top is introduced, which allows the extrapolation of resistivity data to real tube conditions. Information about the Scandate surface complex is evaluated.