  In this paper we present the physical design of the pulsed sextupole
injection system for Beijing Advanced Photon Source (BAPS) with an ultralow
emittance. The BAPS ring lattice is designed in such a way that two options of
pulsed sextupole injection are allowed, i.e., with septum and pulsed sextupole
in different drift spaces or in the same drift space. We give the magnetic
parameters of the injection system and the optimal condition of the optical
functions for both options. In addition, we find that the pulsed sextupole
induces position-dependent dispersive effect and causes non-ignorable effect on
the injection efficiency in a storage ring with a relatively small acceptance,
which should be well considered.
