PHOTON-STIMULATED DESORPTION MEASUREMENT OF AN EXTRUDED ALUMINUM BEAMCHAMBER FOR THE ADVANCED PHOTON SOURCE

The Advanced Photon Source (APS), presently being commissioned, will p roduce x rays of unprecedented brightness. The high energy ring of the APS is a 7 GeV positron storage ring, 1104 m in circumference designe d to operate at less than 10(-9) Torr with 300 mA of beam and a greate r than 10 h lifetime. The storage ring vacuum chamber is constructed f rom an extruded 6063 aluminum alloy. During the construction phase, a 2.34-m-long section of the APS extruded aluminum chamber was set up on National Synchrotron Light Source (NSLS) X-ray Beamline X28A and phot on stimulated desorption (PSD) was measured. Cleaning and preparation of the chamber was identical to that of the APS construction. In addit ion to the chamber, small samples of Al, Be, and Cu were also exposed to white light having a critical energy of 5 keV. In addition to PSD, measurements were made of the specular and diffuse scattering of photo ns. The chamber and samples were each exposed to a dose greater than 1 0(23) photons per m. Desorption yields for H-2, CO, CO2, CH4, and H2O are reported as a function of accumulated flux, critical energy, incid ence angle, and preparation. These results are compared with previous results for aluminum on NSLS Beamline U10B and PSD results of other la boratories published for aluminum. (C) 1996 American Vacuum Society.