Sey of samples from the dipole chamber of petra III at desy

At the synchrotron radiation facility PETRA III, tune spectra have been measured with some characteristics which are typically observed at other storage rings in connection with electron cloud effects. For some bunch filling patterns, an increase of the vertical emittance has been observed. To estimate such effects with the available e-cloud simulation codes, the detailed knowledge of the SEY (Secondary Electron Yield) of the Al chamber is required. To the purpose, representative PETRA III Al samples were studied in detail at the INFN-LNF Surface Science Laboratory. XPS (X-ray photoelectron spectroscopy) and SEY measurements were performed as a function of electron conditioning. The SEY of the "as received" samples shows a value of ?max = 2.8 at Emax=300 eV. Surface bombardment with electrons (scrubbing) of 500 eV kinetic energy, reduces the SEY to values between ?max = 1.8 to 1.5 (depending on the actual sample analyzed), with, respectively, Emax=325 to 250 eV. The XPS characterization of the sample surface shows clearly that the SEY variation is closely related to the amount of oxygen present on the surface.