Sources of amplitude-dependent tune shift in the PEP-II design and their compensation with octupoles

Higher order contributions from sextupoles and dipole fringe fields, quadrupole fringe fields, kinematic terms in the Hamiltonian and systematic or random multipole errors may degrade the dynamic aperture by shifting the particles in the tune plane in an undesired direction. The authors compare the various sources quantitatively and discuss their impact on the dynamic aperture of the PEP-II low energy ring (LER) lattice. A tunable compensation scheme for the LER lattice, which permits an independent control of the tune shift with amplitude in the two transverse planes is presented.