Ti-Zr-V non-evaporable getter films: from development to large scale production for the Large Hadron Collider

Non-evaporable getter (NEG) alloys after dissolution of their native oxide layer into the bulk are able to pump most of the gases present in ultra-high vacuum systems. The dissolution process, commonly called activation, is obtained by heating in vacuum. NEG materials can be sputter-deposited as a thin film on the inner wall of a vacuum chamber, transforming it from a source of gas into an effective pump. The most significant advance in the development of NEG films was the discovery of a very low activation temperature (180°C for 24 h heating) in a large range of compositions of the Ti-Zr-V system. This favourable property was correlated with nanometric grain size of the film (about 3 to 5 nm). In addition to pumping, NEG films lead to reduced induced gas desorption and secondary electron yields. As a consequence, Ti-Zr-V films provide the optimum solution to most of the problems encountered in vacuum systems of modern particle accelerators for high energy physics and for synchrotron radiation facilities. In the near future the most significant benchmark for Ti-Zr-V films will be the Large Hadron Collider (LHC) presently under construction at CERN, where about 6 km of beam pipe are being coated. A dedicated magnetron sputtering facility has been built to cope with the high number of vacuum chambers (about 1200) and the tight production schedule.