Abstract
The emission stability against ion bombardment and oxygen adsorption was investigated on thermionic Ba-dispenser cathodes with different top layers (W, Os/Ru, Re, Ir, and Re+Sc2O3) as a function of temperature and oxygen partial pressure. From these data, Ba and BaO reactivation energies and oxygen desorption energies were derived. During ion bombardment, two degradation/regeneration channels were observed due to the sequential carrying off of the emitting dipole and the corresponding resupply of Ba and BaO. Also two degradation/regeneration channels were detected during oxygen poisoning due to adsorption of oxygen and oxygen induced desorption of the emitting dipole or parts thereof and corresponding oxygen desorption and regeneration of the BaO dipole. The different top layers showed Ba and BaO reactivation energies of 1.5–2.6 and 2.0–2.93 eV, respectively. The values determined from the poisoning measurements were 0.3–0.7 eV larger that those from ion bombardment measurements. The oxygen desorption energies were between 1.5 (Sc/Re) and 2.91 eV (W).
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