Mitigation of coherent beam instabilities in CEPC

The collective beam instabilities are potential restrictions in the Circular Electron Positron Collider (CEPC) to achieve high luminosity performance. These instabilities can induce beam quality degradation or beam losses. Different strategies used to mitigate these effects are discussed. The impedances of the dominant contributors are carefully designed and optimized to either reduce the parasitic power dissipation or increase the beam instability threshold. The bunch filling patterns are also optimized to fight the beam ion instability, the electron cloud build-up and the transient beam loading effect.