Cures of coupled bunch instabilities

To achieve the desired luminosities and brilliances in future storage rings for colliders and synchrotron light sources, very large beam currents need to be stored in many tightly spaced bunches. A serious limitation of the performances comes then from the conventional coupled bunch instabilities (CBI). Energy oscillations and transverse oscillations are mainly driven by high-Q structures and the resistivity of the vacuum chamber. Control of these multibunch instabilities has become a critical issue and various strategies are considered to push up the instability thresholds: HOM frequency control to avoid the overlap of dangerous modes with beam spectrum, heavy mode damping to reduce the resonant buildup of the fields, Landau damping to destroy the coherence of the beam and lastly strong feedback systems operating either in the frequency or time domains. These different cures and their technological developments are reviewed in this short paper.