We have done study on the International Linear Collider damping rings lattice with the aim to reduce the total cost. That includes the comparison between different kinds of arc cells, the simplification of the total lattice structure, decreasing the total magnets number, the design of the dispersion suppressor, and also the dynamic aperture optimization and tune choosing associated studies. From these studies, a full technique on designing and optimizing the large storage ring lattices is established.

To have proper momentum compaction, emittance, beta functions, and phase advance, the arc cell length, total arc cell number, and the drift's length in one arc cell are scanned. At last, 72/72 degree modified FODO arc cell which is 29.4 m long is selected, and the total arc cell number is selected to be 184. The arc cell and dispersion suppressor design are shown in Fig. 1.

**Figure ****1:** (Left): Arc cell design; (Right): Dispersion suppressor design.

After careful considerations of the matching sections between arc and straight, finally an ILC damping ring FODO lattice design is accomplished, with 2/3 number of quadrupoles, same total length of dipoles, less sextupoles, and a half number of cryogenics access shafts in comparison with OCS6 lattice (the baseline design). The layout and total ring TWISS parameters are shown in Fig. 2.

**Figure ****2:** (Left): Layout; (Right): TWISS parameters of the damping ring.

Following some matching criteria and the requirements for selecting a proper working point, the linear lattice matching, chromaticity correction and FMA (Frequency Map Analysis) (dynamic aperture) tracking process are repeated. For* ¦Á*_{p }= 4x10^{-4} case, the DA is about 7 times injected positron bunch size for on-momentum particles, without magnets errors and alignment errors. For *¦Á*_{p} = 2x10^{-4} case, the DA is about 3.5 times injected positron bunch size and under optimization.

The advantage of this design is that: with the whole lattice unchanged, by only adjusting the power supply of the quadrupoles, the momentum compaction of the FODO damping ring can be tuned between 2x10^{-4} and 6x10^{-4}; accordingly the phase advance of one arc cell is tuned between 90/90 degree and 60/60 degree.