Non Evaporable Getter (NEG) Coatings for Vacuum Systems in Synchrotron Radiation Facilities

Abstract

Non evaporable Getter (NEG) films, sputter deposited onto the internal surfaces of vacuum chambers, have been proposed by CERN to substantially reduce the gas pressure in UHV‐XHV systems. The NEG film acts as a conductance‐free distributed pump inside a chamber. Being a barrier for gases it also reduces thermal out‐gassing, thus allowing the achievement of very demanding pressure conditions. These features are ideal for very narrow, conductance limited chambers, like Insertion Devices, which cannot be always efficiently pumped by ordinary means. Recent investigations have also shown that NEG coatings do present additional interesting features, like low secondary electron yield and low gas de‐sorption rates under ions, electrons and photons bombardment, compared to traditional technical surfaces. Experimental tests, carried out in several high energy machines and synchrotron radiations facilities have so far confirmed the benefits of NEG films in term of better vacuum, longer beam life time and stability, simplified machine design, reduced conditioning time and overall improved machine performances. For these reasons, NEG coating technology is now gaining increasing attention and it is seriously considered for upgrades in a number of machines and for future projects. In the present paper, we report SAES getters experience on NEG coating of chambers of different geometries, materials and sizes for a variety of projects related to synchrotron radiation facilities. Examples of applications in various machines, as well as typical issues related to chambers preparation, film deposition, quality control and characterization, are given.