Performance of a notch filter for BEPCII

The high beam current (0.9 A) and the large number of bunches (93 bunches) may cause coupled bunch instabilities (CBI) in BEPCII. Active feedback systems are required to suppress CBI. The BEPCII transverse feedback system mainly includes three parts that are the signal detection unit, the signal processing unit, and the kicker. The notch filter is an important part of the signal processing unit. In this paper a simple notch filter which is combined with two cables, a splitter and a combiner is introduced. And a -41 dB notch depth is achieved. Transverse feedback system with this notch filter succeeds in curing the instability of the beam. It is proved that the filter can satisfy the requirement of the BEPCII transverse feedback system.