Compensation of bunch position shift using sub-RF cavity in a damping ring

In the damping rings of future linear colliders, bunches will be filled along the ring in a bunch-train configuration, where spacing between trains is much larger than bunch-to-bunch spacing in a train. Because of this configuration, beam loading in RF cavities will cause the shift of bunches from their nominal longitudinal positions. The shift can be compensated with an active or a passive RF cavity whose resonance frequency is well controlled. By tracking simulations, the method is demonstrated for ATF damping ring at KEK