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

Abstract

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.

Carbon coatings with low secondary electron yield

“…NEG is successfully applied in most of the room temperature sections of the Large Hadron Collider (LHC) [9]. In some situations, such as in the case of the Super Proton Synchrotron (SPS) at CERN or in space applications, thermal activation is not possible because of limitations imposed by the constituent materials of the systems or the available power.…”

Activation characterization of non-evaporable Ti–Zr–V getter films by synchrotron radiation photoemission spectroscopy

“…In order to upgrade and sustain the vacuum inside the cavity of vacuum-type devices, non-evaporable getter (NEG) materials, such as titanium or titanium alloys, have been widely used due to their low activation temperature, high chemical activity, large solubility, and high diffusivity for gases [1][2][3][4][5][6][7]. When the NEG materials are exposed to air, their surfaces will be covered by the reactive molecules, such as oxygen, carbon dioxide, etc.…”

“…The activation temperature of the NEG can be characterized by the ultimate pressure of the vacuum cavity [1,3] and the fully metallic surface state by surface examination by X-ray photoelectron spectroscopy (XPS) [4,5,7], static secondary ion mass spectroscopy (SSIMS) [4,5], and Auger electron spectroscopy (AES) [2,6]. It is well known that the Ti x Zr y V z alloy with a well-defined composition range has the lowest activation temperature of 180°C with an activation time of 24 h [1][2][3]6].…”

Contributed Review: The feasibility of a fully miniaturized magneto-optical trap for portable ultracold quantum technology

“…Heating the NEG in vacuum, known as activation, causes these compounds to diffuse into the bulk leaving a fresh metallic surface pump. Typical oxygen solubilities for NEG compounds are on the order of 10%, so a 1 µm thin film can undergo ∼100 reactivation cycles after air exposure, however the pumping efficiency begins to reduce after a few cycles 114 . This corresponds to an approximate total capacity of 10 12 molecules per cubic centimetre.…”

“…For our MicroMOT design this can lead to a monolayer coverage of oxygen on the NEGs and result in saturation. It should be noted that oxygen penetrates the NEG surface resulting in a capacity of about five monolayers 114 . Therefore it is important to maintain the chip at high temperatures after bonding to absorb the oxidized NEG layers into the bulk.…”