PHOTON DESORPTION MEASUREMENTS OF COPPER AND COPPER PLATED BEAM TUBESFOR THE SSCL-20 TEV PROTON COLLIDER

Relativistic protons circulating in the SSCL 20 TeV collider emit sync hrotron radiation (10(16) photons/m/s, E(crit) = 284 eV). This radiati on will photodesorb gases from the walls of the beam tube. The 4.2 K s uperconducting magnet bore tubes will act as very long distributed pum ps. Build up of cryosorbed gases could severely limit collider operati on and may require a bore tube liner to hide cryosorbed molecules from the photon flux and to increase the H-2 pumping capacity. To predict collider vacuum performance, photon stimulated desorption experiments have been running at the National Synchrotron Light Source (NSLS) at B NL and on the VEPP2M storage ring at BINP, Novosibirsk, Russia. At the U10B beamline of the VUV ring at NSLS, beam tube samples were exposed to over 10(23) photons/m with E(crit) = 486 eV and incident angle = 1 2 mrad. Unbaked copper and copper plated stainless steel have been tes ted. In addition, results have been obtained with a 1100 G dipole magn etic field and with a 350-degrees-C vacuum bake. Results are presented and compared with other measurements at the NSLS and at other laborat ories.