VUV synchrotron radiation studies of candidate LHC vacuum chamber materials

For the design of future accelerators, in particular, the beam vacuum of th e large hadron collider (LHC), a 27 km circumference proton collider to be built at CERN,'white light' (WL) and monochromatic VUV synchrotron radiatio n (SR) have been used to measure, both qualitatively and quantitatively, el ectron emission from candidate vacuum chamber materials. Emphasis has been placed on measuring the photoelectron yields (PY) and the energy distributi on of the emitted electrons. These parameters are relevant to gas desorptio n, the LHC cryogenic cooling capacities and the possible creation of an ele ctron cloud which may cause beam instabilities. Proposed materials, prepare d on an industrial scale, such as 50 mu m OFE Cu co-laminated onto a high M n-content stainless steel, exhibit significant modifications when exposed t o the WL spectrum from the BESSY TGM7 beamline. Surface cleaning treatments , such as sample annealing and ion bombardment, induce substantial changes to the electron emission which therefore indicate that such surfaces would not be constant, in terms of electron emission, during machine operation. S urfaces which are considered to be constant electron emitters, such as anne aled TiZr alloys and commercial non-evaporable getters, were also investiga ted. These results and their implications for the choice of the material to be used for the LHC are discussed. (C) 1999 Elsevier Science Ltd. All righ ts reserved.