Dynamic shielding during ion bombardment of Ba dispenser cathodes

Ion bombardment IB.resistivity is a key parameter for cathodes to be operated in TV tubes and CMT’s over lifetimes of several years. Thus, accelerated stress tests with much higher ion dose rates than those present in real tube environment are normally used. Here, IB resistivity of OsrRu-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 complexrdipole below Ba. Enhanced IB resistivity w.r.t. total ion dose was observed for reduced ion dose rates. Based on a model of shielding an extrapolation from stress tests to real tube conditions has been established, where the correction factor is in the range of 1–8, depending on the test conditions. q1999 Elsevier Science B.V. All rights reserved.