AVS 59th Annual International Symposium and Exhibition
    Vacuum Technology Tuesday Sessions
       Session VT-TuM

Paper VT-TuM12
Improving the Pump Down of UHV Systems by the Additional Pumping Speed Provided by NEG Pumps

Tuesday, October 30, 2012, 11:40 am, Room 14

Session: Pumping, Gas Dynamics and Modeling
Presenter: F. Siviero, SAES Getters, Italy
Authors: F. Siviero, SAES Getters, Italy
A. Bonucci, SAES Getters, Italy
A. Conte, SAES Getters, Italy
L. Caruso, SAES Getters, Italy
L. Viale, SAES Getters, Italy
P. Manini, SAES Getters, Italy
Correspondent: Click to Email
The study of pump down processes is one of the basic topics of vacuum technology since its early days. Its relevance from the practical point of view is very high in a variety of systems including large machines like accelerators, surface science equipment, scanning/transmission electron microscopes and many other analytical systems and sealed off devices. At present the bake-out of these systems may require days to weeks, resulting in a considerable use of time and energy. Here we report on a series of experiments aimed at investigating how an increase of the total pumping speed during the pump down influences the behaviour of the main gases of interest, i.e. water and hydrogen. Several pumping configurations are compared, including turbo molecular pumps, large sputter ion pumps (SIP), Non Evaporable Getter (NEG) and a new SIP/NEG combination pump called NEXTorr® [1]. The most relevant desorption models and their predictions for the pump down processes are expressed in an explicit form and compared with the experiments.The results of the study confirm that water desorption can largely benefit from an increase of the available pumping speed, due to the reversible nature of its adsorption kinetics. As far as hydrogen is concerned, a higher pumping speed at the end of the bake provides a lower partial pressure. This translates into the possibility of either reducing the duration of the bake-out process or improving the ultimate achievable vacuum, both issues having practical interest in vacuum systems for research and industrial applications.
[1] NEXTorr is an International Trademark registered by the “Madrid System” property of SAES Getters S.p.A.