Abstract
The theory and design are discussed of getter-ion pumps, in which gas is exhausted by sorption in metal layers in the presence of an ionizing electron stream. The development of getter-ion pumps is traced from the early observations of gas absorption in glow-discharge tubes and sputtered and evaporated deposits. The effects of activating the residual gas by ionization are discussed and it is shown that only a limited number of gas-metal pairs are known where this enhances the sorption rate. Generally, the speeds of oxidizing reactions are not influenced by activation. Inert gases, which cannot be directly sorbed by the getter, may be ionized and their positive ions transported to a target, where they may be embedded or covered by metal films. The sorption and deposition properties of a range of getter materials are surveyed, and it is shown that titanium, barium and calcium may be used in evaporation type pumps. Methods of continuously replenishing the gettering surface by vacuum evaporation and cathodic sputtering in a range of pumps are described. The use of getter-ion pumps with mechanical and diffusion pumps for pre-exhaustion and obtaining very low pressures are discussed, and factors limiting the ultimate pressure considered. The performance of getter-ion pumps is compared with that of diffusion pumps and it is shown that getter-ion pumps may be used where the gas throughput is small, e.g. attaining ultra high vacuum in degassed envelopes and maintaining the vacua in electronic apparatus of limited volume.