CAS, Inst High Energy Phys, Beijing 100049, Peoples R China
Electron cloud instability (ECI) may take place in a storage ring when the machine is operated with multi-bunch positively charged beam. According to the actual shape of vacuum chamber in BEPC II, a computer simulation program has been developed. With the code I the electron density in the chamber with the different widths of antechamber and the different secondary electron yields, respectively, can be obtained. The possibility to put clearing electrodes in the normal chamber or ante-chamber to reduce the electron density in the central region of the chamber is also investigated. In the simulation, the coherent oscillation of bunches and the formation of electron cloud (EC) are tracked simultaneously. The sideband distribution and growth rate can be obtained through tracking and dealing the bunch oscillation amplitude with FIT. Based on the head-tail model, the single bunch instability induced by EC is also studied. By the simulation, for BEPC H the threshold density for the single bunch instability is estimated to be similar to 10(12)m(-3) and the restraining measures that might be adopted in BEPC 11 can control the EC density under the threshold. According to the simulation results, a relatively big positive chromaticity should be used to suppress the bunch blow up.