Superconducting magnets in the interaction region of the KEK B-Factory

The interaction region of the KEK B-Factory requires four superconducting magnets (two dipoles and two quadrupoles). Due to their detrimental effect on the experimental detector, the leakage field of the magnets needs to be as small as possible. For achieving this smaller leakage field, we have designed special iron-free dipoles with an active shield coil. Due to the active shield method, the stray field of the magnets is suppressed to a level of 10 mT outside the radius of 0.25m. The quadrupoles are also iron-free magnets, but have no shield coil. This paper presents the results of the two- and three-dimensional electromagnetic studies along with the structure of these magnets.