Comparison of the synchrotron radiation induced gas desorption in aluminum vacuum chambers after chemical and argon glow discharge cleaning

In a dedicated synchrotron radiation beam line at the DCI storage ring at Orsay, France a series of measurements were made to evaluate the effect of argon glow discharge cleaning either as a pretreatment in the laboratory, or in situ, following the installation and pumpdown of the vacuum system in the LEP (Large Electron Positron storage ring) machine. On exposure to synchrotron radiation the gases desorbed were H2, CH4, CO, and CO2 with Ar in the glow discharge cleaned chambers. With continued exposure the gas desorption decreased with time except that the Ar showed a definite reluctance to clean up. When applied to LEP conditions, chemical cleaning only gave the required beam-gas lifetime after the shortest exposure. The worst overall situation results from the in situ Ar discharge cleaning due to the low pumping speed for Ar in the LEP machine