Barium transport process in impregnated dispenser cathodes

An impregnated dispenser cathode is a dynamic system in which the continuous loss of barium from the emitting surface must be compensated for by a surface diffusion supply process. A review of the effect of these processes on certain surface characteristics is given in this paper. A derivation is then presented indicating that inside the porous matrix, surface diffusion may be the dominant transport mode rather than the Knudsen flow, which has been emphasized previously. We discuss our experimental approach for determining the surface diffusion coefficient and present data that indicate that the surface diffusion transport process can be severely slowed by some surface species, which most likely is oxygen.