Recent progress in the development of the bunch feedback systems for KEKB

In KEKB, which is a B-factory project at KEK, the bunch spacing is very short, only 2 ns, and the number of the bunches comes up to about 5000 per ring. In order to cure the instabilities due to the high beam current, we will use bunch feedback systems in KEKB rings. Recently we developed the new position detection system and made a prototype of the signal process system for the feedback systems. Using these tools and accelerating cavities as the kicker we performed an experiment for checking a longitudinal feedback system. The Robinson instability which was intentionally excited was successfully damped with a short damping time.