Beam-gas lifetime in a low emittance, medium-energy storage ring

In order to understand the beam-lifetime limiting process in a medium-energy machine like the 2 GeV Pohang Light Source, the beam-gas scattering effects have been measured by using He gas and the effects of the transverse aperture height on the lifetime have also been examined by using a beam scraper. It is found that for a medium to large gap vacuum chamber the lifetime is mainly limited by the Touschek effect at the machine operating pressure, low 10/sup -9/ Torr. For a very small gap undulator, however, the beam-gas scattering makes substantial contribution to the beam lifetime even at /spl sim/1/spl times/10/sup -9/ Torr because of Coulomb scattering.