AVS 52nd International Symposium
    Vacuum Technology Wednesday Sessions
       Session VT-WeA

Paper VT-WeA3
Pumping Speed Measurement of TiZrV Coated Pipes

Wednesday, November 2, 2005, 2:40 pm, Room 201

Session: Hydrogen, Outgassing, and Vacuum Systems
Presenter: A. Bonucci, SAES Getters S.p.A., Italy
Authors: A. Bonucci, SAES Getters S.p.A., Italy
A. Conte, SAES Getters S.p.A., Italy
Correspondent: Click to Email
In the last few years the interest of the particle accelerators community towards ZrTiV non evaporable getter (NEG) coatings of vacuum chambers has been continuously increasing. With the increase of the interest, also the number of characterizations of this coating from several final users is increasing. One of the key characterizations is the measure of the actual pumping speed of the NEG coating. The typical method used to measure the pumping speed of a getter is described in the ASTM F798-82. Normally, it has been applied onto a discrete sample coated during the process. This approach is not suitable with NEG coated vacuum pipes. An improved experimental configuration for sorption tests is here first described. The method is based on the ratio measurement of pressures at the inlet and the outlet of a coated pipe. A calibration curve permits to evaluate sticking probability of the coated surface from the pressure ratio. A mono-dimensional model is often used in order to obtain the calibration relationship; for high sticking probability this approach is not more suitable. We will show that a three dimensional mathematical model, based on the angular coefficients approach, is needed to calculate the gas distribution inside a vacuum vessel and the relationship between the pressure ratio and the specific pumping speed of the coated surface.