Analysis of transverse beam oscillation at Photon Factory

At KEK photon factory, FPGA based bunch by bunch feedback system to cure the transverse instabilities has been operating stably since Oct. 2005. Specification and performance of the system will be introduced here. Up to 640 k turns data can be stored in the buffer for each bunches, transient measurement has been done to analyze the instability modes under different beam conditions, which helps to understand the instability sources. A new generation digital BPM electronics (Libera) has also been evaluated at photon factory, which can give the beam position data at different bandwidth simultaneously. Bunch by bunch beam oscillation, together with the digital turn-by-turn beam position measurement, injection oscillation damping is recorded and analyzed, transverse beam oscillation with and without the bunch by bunch feedback system will be shown in this paper. With turn by turn beam position data, many machine physics parameters can been measured, one example is the precis tune measurement; centre of mass of the bunched beam can been plotted in phase space, from which the nonlinear beam dynamics can be revealed.