Dynamic shielding during ion bombardment of Ba dispenser cathodes

Ion bombardment (IB) resistivity is a key parameter for cathodes to be oper ated in TV tubes and CMT's over lifetimes of several years. Thus, accelerat ed stress tests with much higher ion dose rates than those present in real tube environment are normally used. Here, IB resistivity of Os/Ru-I and top layer Scandate cathodes was investigated. It was observed by variation of the dose rates, that Ba resupply modified the survived ion dose and led to a dynamic shielding of the rest of the surface complex/dipole below Ba. Enh anced IB resistivity w.r.t. total ion dose was observed for reduced ion dos e rates. Based on a model of shielding an extrapolation from stress tests t o real tube conditions has been established, where the correction factor is in the range of 1-8, depending on the test conditions. (C) 1999 Elsevier S cience B.V. All rights reserved.