critical issues in ensuring reproducible and reliable deposition of NEG coatings for particle accelerators

Non evaporable getter (NEG) coating technology, developed at CERN in the late 90s´, is an effective pumping solution for conductance limited vacuum chambers. It reduces thermal out-gassing and provides distributed pumping ability, allowing the achievement of very low pressure. NEG films do show additional interesting features, like low secondary electron yield and low gas de-sorption rates under ions, electrons and photons bombardment. For these reasons, large scale adoption of NEG coated chambers is now a reality and several leading edge machines will soon benefit from it. A critical issue for the successful application of this technology is the ability to deposit NEG coatings in a reproducible and reliable way all along a pipe. This is particularly important for narrow-gap or specially shaped chambers which pose severe challenges in term of film thickness distribution, chemical composition and sorption properties. A dedicated study was carried out to fully understand the deposition process as a function of the sputtering parameters and the chamber geometry. Results obtained do allow optimizing the coating process.