The Pep-II B-Factory septum quadrupole magnets

The PEP-II B-Factory is presently engaged in the design and fabrication of several unique magnets referred to as septum quadrupoles. This family of magnets is required to contain a low energy beam of positrons (3.1 GeV) and a high energy electron beam (9.0 GeV) in adjacent beam pipes housed within a common magnet. One beam will be focused while the other passes through an almost field free region. To do this, an asymmetric magnet must be designed having a pure, high quality quadrupole field in the magnet aperture and an adjacent low field bypass channel. A current sheet or “septum” coil must be placed between these two regions to produce the desired magnetic results. Design of this high current density septum coil presents many challenges since space between the two vacuum beam pipes where the coil must reside is very limited. This paper will describe the overall design of the septum quadrupoles and the solutions employed to achieve the required magnetic performance