Distributed ion pump testing for PEP-II, asymmetric B-factory collider

At its design level, PEP-II will circulate asymmetric beams at 9 GeV and 1.5 A in a High Energy Ring and 3.1 GeV with 2.1 A in a Low Energy Ring. In addition, the vacuum systems of both rings will be designed to operate at a maximum current of 3 A to provide for higher current operation in the future. Pumping for both rings is provided by sputter ion pump systems. In the High Energy Ring, high gas loads, deriving from the intense photon radiation, are calculated at 1.06×10^-6 Torr liters s^-1 m^-1 using a desorption coefficient (eta) of 2×10^-6 molecules photon^-1. To maintain an average pressure of 5 nTorr or less in the are cells, lumped ion pumps are used in the 2 m long straight sections and distributed ion pumps are used in the 6 m long dipole chambers where the conductance of the vacuum chamber is prohibitively low. To achieve these pressures, the distributed ion pump system is required to have pumping speeds of 110 liters s^-1 m ^-1 however, a design level of 165 liters s^-1 m^-1 has been set to provide a factor of safety of 50% based on pumping alone