Paper VT-ThM3
How to Efficiently Combine Ion Pumps and Getter-Palladium Thin Films

Thursday, October 18, 2007, 8:40 am, Room 618

Non-evaporable getters (NEG) have been extensively studied in the last years for their sorption properties towards many gases. In particular, an innovative alloy produced in the form of thin films by magnetron sputtering was developed and characterized at the European Center of Nuclear Research (CERN). It is composed of Ti-Zr-V and protected by an overlayer of palladium (Pd), according to a technology for which we got the license. The use of NEG-Pd thin films in combination with ion getter pumps allows to obtain a simple and easy to handle pumping device for UHV and XHV applications. In order to show how it is possible to apply this coating technology to the internal surface of different types of ion pumps, several tests were carried out on pumps of various shape, size (in terms of nominal pumping speed) and type (diode, noble diode and triode). A special care was taken during the thermal cycle of bakeout and activation of the pumps, in order to preserve the internal film from the contamination due to the sputtering of the cathodes and/or from the interdiffusion of its components. Some important remarks about the most appropriate conditions of pressure and temperature will be discussed. The performances of the NEG-Pd coated ion pumps were evaluated in terms of ultimate pressure, nitrogen and hydrogen pumping speed. The contribution of the thin film is particularly relevant for the pumping of this last gas, due to its high sticking factor for palladium and to the great sorption capacity of the underlying getter. Finally, the possibility of further improvement of the performances by substituting the palladium with other Pd-based alloys will also be evaluated.