Design of the PEP-II low energy ring vacuum system

A vacuum system based on the antechamber approach is being designed for the PEP-II, B-factory, Low Energy Ring are sections to be installed at the Stanford Linear Accelerator Center. Pressures in the six are regions are to be less than 10 nanotorr at a nominal positron beam energy of 3.1 GeV and current of 3 amperes. The high energy and large beam current result in high gas loading due to photon induced gas desorption. The antechamber design allows 90% of the photons and over 99% of the synchrotron radiation power to be dumped on special photon stops away from the main beam chamber and close to vacuum pumps. The high photon flux at the stops gives the added benefit of quickly scrubbing these surfaces, further reducing the outgassing