COMPARISON OF PHOTODESORPTION YIELDS USING SYNCHROTRON-RADIATION OF LOW CRITICAL ENERGIES FOR STAINLESS-STEEL, COPPER, AND ELECTRODEPOSITEDCOPPER SURFACES

Photon-stimulated gas desorption yields from metal surfaces, typically used in large vacuum systems, such as stainless steel, copper, and el ectrodeposited copper, have been measured using synchrotron radiation with critical energies from 12.4 to 284 eV, thus allowing to obtain in itial yields applicable to future large hadron colliders. The main gas es desorbed from all surfaces are: H-2, CO2, CO, and CH4. Water is als o desorbed and greatly increases with exposure until a saturation valu e is reached. In situ bakeout reduces the amount of water desorbed, bu t only slightly reduces the yield of the other gases. The dependance o f the yields on critical energy is almost linear, except for H2O. Phot oelectron yields have also been measured, showing a good linear relati on with the pressure increase, thus suggesting a process where a photo n produces an electron that subsequently desorbs a gas molecule.