Lawrence Berkeley National Laboratory

Designing a lattice with sufficient dynamic aperture for the ILCDamping Rings is very challenging as the lattice needs to provide a small equilibrium emittance and at the same time a large aperture for the injected beam (including a large momentum acceptance). In addition, outside constraints have forced layout changes in the damping ring. Some of the layout changes had an impact on thedynamic aperture. In order to better understand the changes indynamic aperture, frequency maps are studied. Those studies can help in identifying the reason for the changed dynamic apertureand in finding a good location for the betatron tunes and determining an upper limit for the chromaticities. A summary of recent studies and suggestions for improving the dynamic aperture bychoosing a different tune are presented.