Chemical cleaning of aluminum alloy surfaces for use as vacuum materials in synchrotron light sources

Abstract

Photon and electron desorption from the vacuum chamber walls of electron storage rings such as the proposed Advanced Photon Source (APS), are sometimes responsible for the production of large gas loads during operation even in systems with very good static vacuum. The gas released by beam-induced desorption results in scattering of the beam electrons, and a consequent reduction in the beam lifetime. In extreme cases, the beam-induced outgassing may cause so much scattering that it is not possible to obtain the design goals with regard to obtainable beam current. Consequently, it is important that the surfaces which are exposed to the electron beam and photon fluxes contain as little trapped gas as possible, and that the gas burden during operation be kept as low as possible. The current study investigates the effectiveness of a chemical cleaning treatment developed at CERN for the LEP storage ring, as applied to the 6063 alloy to be used in APS. Additionally, depth profiling of the chemically cleaned samples and samples which were vapor-degreased only, provides new insight on the cleaning process as it applies to the alloy proposed for use in APS. 14 refs., 8 figs., 1 tab