In recent years a new innovation to improve the performance of the 'vacuum vessel' has been the development of a vacuum chamber with a Non-Evaporable Getter (NEG) coating magnetron sputtered onto the inner walls [1-3]. This technique was intensively developed at CERN and is now widely used in a number of electron accelerators [4] for narrow gap insertion device vessels where conductance limitations restrict the pumping speed available and cause a pressure rise resulting in increased gas bremmstrahlung. This new technique is still in its infancy and there are a number of issues which are still not yet fully understood. A number of unanswered questions remain for accelerators with regard to NEG coatings including how they can be optimised to exhibit low photon, electron and ion stimulated desorption yields and reduce secondary electron emission.
The benefits of NEG coated vacuum chambers for accelerator vacuum systems led to a fundamental study of NEG coating research in the UK between ASTeC and MMU. This paper looks at the delicacy of producing NEG coated chambers and how the method of activation and regeneration of such coatings can have a significant impact on the end result. Identical NEG films were sputtered onto both planar and tubular samples with significant differences observed between the two in terms of both pumping capacity and sticking coefficients. Critical issues such as the ratio of NEG coated to uncoated surface will also be presented.
[1] C. Benvenuti, J.P. Bojon, P. Chiggiato and G. Losch, Vacuum, 44, 507 (1993)
[2] C. Benvenuti and F. Francia, J. Vac. Sci. Technol. A 6 (4), 2528 (1988)
[3] C. Benvenuti and F. Francia, J. Vac. Sci. Technol. A 8 (5), 3864 (1990)
[4] R.Kersevan. "Performance of a narrow-gap, NEG-coated, extruded aluminium vacuum chamber at the ESRF." Proc. of EPAC-2000, Vienna, Austia, p. 2291.
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