  The baseline design for the High Energy Photon Source has been proposed, with
an emittance of 60 pm.rad within a circumference of 1.3 kilometers.
Nevertheless, the nonlinear performance of the design needs further
improvements to enlarge both the dynamic aperture and the momentum acceptance.
In this study, genetic optimization of the linear optics is performed, so as to
find all the possible solutions with weaker sextupoles and hence weaker
nonlinearities, while keeping the emittance at the same level as the baseline
design. These obtained solutions enable us to explore the dependence of
nonlinear dynamics on the working point. The result indicates that with the
same layout, it is feasible to obtain much better nonlinear performance with a
delicate tuning of the magnetic field strengths and a wise choice of the
working point.
