PHOTODESORPTION FROM COPPER, BERYLLIUM, AND THIN-FILMS

Ever increasing circulating currents in electron-positron colliders and light sources demand lower and lower photodesportion (PSD) from the surfaces of their vacuum chambers and their photon absorbers. This is particularly important in compact electron storage rings and B meson factories where photon power of several kW cm-1 is deposited on the surfaces. Given the above factors we have measured PSD from 1 m long bars of (a) solid copper and solid beryllium, and (b), TiN, Au, and C thin films deposited on solid copper bars. Each sample was exposed to about 10(23) photons/m with a critical energy of 500 eV at the vacuum ultraviolet ring of the National Synchrotron Light Source. PSD was recorded for two conditions: after a 200-degrees-C bakeout and after an Ar glow discharge cleaning. In addition, we also measured reflected photons, photoelectrons, and desorption as functions of normal, 75, 100, and 125 mrad incident photons.