Optimization of the PEP-II Low-Energy Ring dipoles

The PEP-II Project, a collaboration of SLAC, LBNL, and LLNL, began construction in January 1994. Dipoles for the PEP-II Low-Energy Ring (LER) are being fabricated in China in collaboration with the Institute of High Energy Physics (IHEP) in Beijing. The LER design calls for short dipoles (l_eff=450 mm) with a 63.5 mm gap. As a result, magnetic properties are dominated by end effects and a proper end chamber must be developed. Magnetic measurements using both integral coil and rotating coil techniques were carried out at LBNL on an early dipole prototype to determine the sensitivity of various allowed multipoles to the end chamber shape. Dynamic aperture studies were carried out in parallel to explore the sensitivity of the lattice to these multipoles. By interpreting the measurement results in terms of differences from the baseline chamber, a prescription was developed to “transfer” the results to another prototype dipole more representative of the production magnets. The optimized end chamber shape was validated with a pre-production dipole and full production is under way