Electron-emission yield under electron impact of ceramics used as channel materials in Hall-effect thrusters.

We report measurement of electron-emission yield (EEY) under the impact of electrons on materials of Hall-effect-thruster (HET) interest: BN, BN-SiO2, and Al2O3. The effects of the material aging (under electron irradiation) on the yield of BN and Al2O3 are investigated. The EEY of BN grows with electron exposure, whereas that of Al2O3 reduces. A simple analysis of our experimental results indicates that these variations are most likely because of surface and near surface composition changes caused by the electron beam. The representativeness of EEY measurements on ceramics that have not suffered from the specific environment of a HET (ion and electron bombardment) is discussed. [ABSTRACT FROM AUTHOR]