Electron storage ring beam lifetime dependence on pressure and pumping speed

The beam loss in electron storage rings depends to a large extent on the interaction of the beam with heavier residual gas molecules such as CO, CO2, and A due to bremsstrahlung and Coulomb scattering. The gas density inside the vacuum chamber is determined by the surface condition of the vacuum chamber, which is bombarded by photons (synchrotron radiation) generated by circulating electron beams, and by the installed pumping. During the initial commissioning severe limitations on the achievable beam current were observed due to large pressure rises. The x-ray ring was shut down for several months and its vacuum system was updated and baked out. Residual gas spectra obtained after the shut down were typical of a well baked out system, i.e., hydrogen constituted approx.95% of the gas and the average pressure was in the 10-10 Torr range. During initial operation the composition of desorbed gases was 43% H2, 25% CO, and 16% CO2 and CH4. After 3 months of beam conditioning the desorption rate dropped by a factor of 5 and the CO, CO2, and CH4 peaks represented smaller percentage of total desorbed gas. Beam lifetime did not, however, show a corresponding increase