Influence of the cathode materials on the sorption of noble gases by sputter-ion pumps

The pumping performances for noble gases of several sputter-ion pumps have been investigated, focussing in particular on the effects generated by the use of different cathode metals. As several papers dealing with the well-known theory of high-energy neutrals suggest, the ratio between the atomic masses of gases and metals is a key factor in terms of pumping speed and possible onset of instability phenomena. Pumping speed data collected during these characterisations have been therefore analysed from this point of view, in order to find a correlation which might possibly help to predict the behaviour of several cathode configurations during the sorption of different noble gases. Ar and Ne pumping speeds after saturation were found to be linearly dependent on the mean atomic mass of the cathode materials. Conversely, He does not seem to adhere to this scheme, probably due to its different pumping mechanisms.