Characterization of a cesium surface ionization source with a porous tungsten ionizer. I

A cesium surface ionization source of the type and geometry customarily used in conjunction with sputter‐type negative heavy ion sources has been characterized. Measurements have been made of positive‐ion production and probabilities of ionization as functions of extraction voltage and cesium oven temperature for ionizer porosities of 0.7 and 0.8. The perveance P of the source, when operated in the space‐charge‐limited regime with the ρ=0.7ρ0 ionizer, is found from experiment to be 7.61×10−4 μP, while that for the ρ=0.8ρ0 ionizer is 1.92×10−4 μP. These values are lower by factors of 3.88 and 15.53, respectively, than those predicted by numerical solution to Poisson's equation for full area emission from the source. Positive‐ion current versus ionizer temperature data are also presented along with mechanical design features of the source.