Secondary electron yield on cryogenic surfaces as a function of physisorbed gases

Electron cloud is an important limitation for the operation of particle accelerators with intense positively charged beams and short bunch spacing. It occurs if the secondary electron yield (SEY) of the beam-pipe inner wall is sufficiently high to promote electron multiplication. At low temperatures SEY is strongly influenced by the physisorbed gases and by the corresponding surface coverage. These conditions are relevant in accelerators operating with superconducting magnets and cold vacuum sections, such as for instance the Large Hadron Collider. This work investigated the variation of SEY of copper, aluminum, and electropolished copper as a function of physisorbed N-2, CO, CO2, CH4, Kr, and C2H6 at cryogenic temperatures. The results of the various gases are compared in order to find a rationale for the behavior of the secondary electrons for various adsorbates. (C) 2012 American Vacuum Society. [http://dx.doi.org/10.1116/1.4736552]