Multipole fields in the antiproton accumulator magnet system

The Antiproton Accumulator is a very large aperture storage ring in which antiprotons are collected over a wide momentum range, stochastically cooled and stacked. The optical properties must be precisely realised and require a variety of high order field components. The very wide aperture and a lack of available space, preclude the use of separate sextupoles and octupoles to provide these corrections. One of the sextupole components was incorporated into the pole profile of the wide elliptic quadrupoles the left-right symmetry of which was thus broken. The other non linear components were produced by variation of the effective length of the dipoles and quadrupoles and achieved in practice with detachable end shims.