Secondary electron emission, surface composition and modes of activation of metal alloy cathodes

The interrelation between the secondary electron emission, the elemental composition of the surface, and the temperature heating history has been studied for cathodes made from alloys based on platinum or palladium containing 1.5–2% barium. These cathodes, which are used at low operating temperatures in magnetron amplifiers and oscillators, were tested in the form of foil disks diffusion bonded to molybdenum or copper. The following modes have been shown to result in optimum secondary electron emission: 1.5 to 2 h at 900 to 950°C for PdBa and 1.5 to 2 h at 1100 to 1150°C for PtBa. To activate the cathode by electron bombardment the following modes may also be used: bombardment power density of 85 to 100 W/cm2, temperature = 450 to 400°C, for 5 h, or 200 to 250 W/cm2, 650 to 600°C, for 1 h.