Design of longitudinal feedback system kicker for the PLS storage ring

The higher order modes (HOMs) of RF cavities at the Pohang Light Source (PLS) storage ring cause longitudinal coupled bunch mode instabilities (CBMIs). To cure these instabilities, a longitudinal feedback system (LFS) is introduced. As a key component of the LFS, there is a single-ridged waveguide-overloaded cavity as a longitudinal bunch-by-bunch LFS kicker for the PLS storage ring. To damp any coupled bunch modes, the bandwidth of this kicker should be wider than 250 MHz. Also, the higher shunt impedance of the kicker is selected to use lower power amplifier. One aluminum kicker is fabricated and the bandwidth, HOMs, and shunt impedance of the kicker are measured with a network analyzer. This kicker has several different features from LFS kicker for DAΦNE. First of all, there are 4 input/output ports to obtain a wider bandwidth. Secondly, there is a nose cone to obtain higher shunt impedance. Finally, the symmetric frequency response of the shunt impedance around central frequency is provided. According to the simulation result done by HFSS code, high shunt impedance of 620 Ω (transit time factor considered value) and the wide bandwidth of 255 MHz are obtained. These are compared with the measured result