During the year 2000, the Vacuum Group of the Technical Services Division carried out research and development in the field of NEG-coated vacuum chambers, mainly for low-gap, insertion-device chambers. For this R&D, a collaboration project with CERN has started. The idea behind it was to take advantage of the low photo-desorption yield and pumping effect of NEG-coated vacuum chambers.

NEG, an acronym for Non-Evaporable Getter, is a class of materials which display peculiar vacuum performances, such as pumping and low molecular desorption yield under electron or photon irradiation.

The ESRF has been faced, in the last few years, with the need to reduce the gap of the insertion devices in order to improve the spectral properties of the photon beam delivered to the Users. Vacuum-wise, this has resulted in designing new vacuum chambers with smaller vertical dimensions. This spatial limitation has, in turn, posed severe constraints on the pumping configuration of such chambers, the most noteworthy being a lack of distributed pumping. This lack of pumping produces a higher pressure profile along the chamber, and the 6 GeV electron beam, interacting with it, generates a higher-than-normal radiation background in the experimental hutches, thereby significantly constraining the operation of the beamlines concerned [1]. 

At the same time, it has been decided to produce extruded-aluminium vacuum chambers, and to apply the NEG-coating to them. The extruded-aluminium solution, already tested at other laboratories, was believed to allow a better, faster and cheaper production of vacuum chambers. As a result, a prototype vacuum chamber, 5 m long, with an 11 mm inner vertical aperture was installed during the December 1999 shutdown on ID31. It was thoroughly tested during the first four runs of 2000, demonstrating, right from the beginning, that the NEG-coated solution would work. Two similar chambers have been produced and installed since then on ID8 and ID13.

At the end of the year, the NEG-coating procedure was applied to an existing stainless steel chamber (5 m long, with an 8 mm inner vertical aperture), which in the past had shown bad vacuum characteristics. It has been installed on the ID31 test beamline and has again demonstrated the excellent performances of NEG coating. The installation of several of these NEG-coated low gap vessels on the Machine during the year 2001 is now planned.

[1] R. Kersevan, Proc. EPAC-2000 Conference, Vienna, June 2000, page 2289-2291, available at http://accelconf.web.cern.ch/accelconf/e00/PAPERS/THP5B11.pdf.