Abstract
The evaluation of the pumping characteristics of metallic films deposited onto glass surfaces in a vacuum environment is a very important issue for several industrial and research applications. Many years ago, an optimized experimental setup and method were defined to measure the pumping characteristics of barium films inside cathode ray tubes (CRTs). [P. della Porta and F. Ricca, Advances in Vacuum Science and Technology (Pergamon, New York, 1960), Vol. II, p. 661 and P. della Porta and L. Michon, Vacuum 15, 536 (1965)]. However, some technological limitations, related both to the particular experimental configuration and to the method used, prevented the possibility of extending this approach to a more general case, including adsorbing materials different from barium, deposited onto surfaces having a geometry different from that of a CRT. The progress in vacuum technology makes it possible today to use a large variety of components to assemble an experimental vacuum apparatus. Moreover, the availability of powerful computational tools allows the design of the best experimental configuration for any specific purpose. In this work, an approach to the study of the pumping characteristics of an adsorbing film in a vacuum is discussed. An improved experimental configuration is described and a mathematical method, based on the angular coefficients approach, able to suitable calculate the gas distribution inside a vacuum vessel, is proposed. The agreement between the experimental data and the theoretical results obtained in the case of carbon monoxide sorption onto a barium getter surface deposited into spherical glass bulbs having different dimensions is discussed.
Published Version
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