Vacuum Conditioning and Beam Lifetime of the Spring-8 Storage Ring

The installation of the vacuum system of the SPring-8 storage ring was completed during 1996. Most of the vacuum chambers are made of aluminum alloy. The main pumping system is a mixed one consisting of NEG strips, DIP, SIP, and LNP. In addition to the standard treatments for ultrahigh vacuum components, dust-controlled procedure was adopted in the manufacturing and the installation processes. Beam commissioning of the SPring-8 storage ring started in March 1997. Since then an integrated beam dose of 190Ah has been achieved up to now, and correspondingly, the dynamic pressure rise per stored beam current (•P/I) decreased by two orders of magnitude. In the multi-bunch mode a lifetime of 65 hours at 70mA were achieved after two years’ operation. Since the vertical emittance is extremely small, the beam lifetime is limited not only by dynamic pressure but also by Touschek effect even in the multi-bunch mode. The contributions of the gas scattering lifetime and Touschek lifetime are estimated in the case of the SPring-8 storage ring.