Dynamic behavior of thermionic dispenser cathodes under ion bombardment

We have investigated the surface coverage and electron emission of thermion ic dispenser cathodes during 3 keV Ar+ ion bombardment, thereby simulating the bombardment of the cathodes by residual gases that takes place in catho de-ray tubes as used in television sets. During the ion bombardment at the operating temperature of 1030 degreesC, a dynamic equilibrium is establishe d between the sputter removal and resupply mechanisms of the Ba and O atoms that form the dipole layer on the cathode substrate. We demonstrated that the performance of the cathodes under ion bombardment is governed by the O removal and resupply rates. It was found that the Ba resupply rate is almos t an order of magnitude higher than the O resupply rate, but that the Ba ca n only be present on the surface bound to O atoms. Therefore, the Ba/O rati o is approximately equal to unity during the ion bombardment. Based on the investigations of the removal and resupply processes, we proposed a model t hat accurately describes the surface coverage and electron emission during the ion bombardment, including the dependence of the ion flux and cathode t emperature. (C) 2001 American Institute of Physics.