Design of the PEP-II low-energy ring arc magnets

We describe the PEP-II Low-Energy Ring (LER) arc quadrupole and dipole magnets, being designed and built by a Lawrence Berkeley Laboratory (LBL) and Institute of High Energy Physics (IHEP) collaboration. The LER requires 292 “standard” 43-cm long, 10-cm bore aperture laminated quadrupoles. A 2-piece construction was chosen to reduce the influence of assembly tolerances on field quality. Laminations with an optimized pole profile are punched from 1 m×2 m×0.5 mm steel sheet, a standard product in China. The chosen design is patterned after that of the Advanced Light Source (ALS) booster quadrupole. As some of the quadrupoles are run in long strings and others in short strings, two coil types (15-turn and 58-turn, each with several cooling-circuit topologies) are being fabricated. The majority of coils are aluminum but a few quadrupoles require copper coils due to their high excitation. Fabrication, assembly, magnetic measurements and fiducialization will be carried out at IHEP. Dipoles will be fabricated similarly. We require 192 dipoles, 45-cm long, with a magnetic radius of 13.75 m and a good-field aperture of 90 mm; the pole shape is optimized for field levels up to 3.5 GeV beam energy. Coils are an aluminum pancake configuration designed to keep power consumption moderate