Dynamic aperture with multipoles of special magnets in the KEKB interaction region

At KEKB, six quadrupoles of special shapes are placed in the interaction region. Those quadrupoles are accompanied by higher-order multipole components which are prominent sources to degrade the dynamic aperture, and which even affect the linear optics because the design orbit passes through one of the special quadrupoles off-axis. In order to represent realistic field distributions of those quadrupoles obtained by hardware design, we take the higher-order multipoles up to 21st into account in our simulation. Using this model, we have redesigned the linear lattice and have estimated tolerances on the magnitudes of multipole components.