Measurements of photon stimulated desorption from thick and thin oxide of KEKB collider copper beam chambers and a stainless steel beam chamber

Photon stimulated desorption (PSD) from KEKB factory copper chambers was me asured at the National Synchrotron Light Source (NSLS), located at the Broo khaven Laboratory. The KEKB is an asymmetrical collider recently constructe d in Ibaraki, Japan. The collider utilizes two UHV ring chambers. one for a 3.5 GeV positron beam and the other for an 8 GeV electron beam, for B-meso n studies. Two each, 1 m long, 94 mm inner diameter, chemically deoxidized copper beam chambers with conflat end flanges, were provided by KEKB to the NSLS, for measurement of PSD. PSD and specular reflection were measured on NSLS VUV ring beamline U9a. It has been reported that a high temperature a ir bake on large stainless steel vacuum systems reduces the need for a vacu um bake. To determine the effect of surface oxide, following the initial PS D measurement, the chambers were chemically cleaned and then oxidized in ai r for a week at 150 degreesC. PSD was remeasured after the air bake. A simi lar process and measurement was performed on a stainless steel beam chamber , with the exception of oxidation at 450 degreesC. After the chambers were installed on beamline U9a, they were exposed to a minimum of 10(23) photons direct from the source having a critical energy of 595 eV, striking at an incident angle of 100 mrad. The major PSD yields for hydrogen, carbon monox ide, carbon dioxide, methane, and water vapor are reported as a function of accumulated photon flux, incident surface oxide, and chamber preparation. The results are compared with other PSD measurements on NSLS beamlines and those of other laboratory publications for copper and stainless steel. (C) 2001 American Vacuum Society.