Experiment to measure the electron cloud at BEPC

Many experiments on photoelectron instability (PEI) have been carried out at the Beijing Electron Positron Collider (BEPC) in IHEP, China, in collaboration with KEK. Simulations on the PEI with a physical model give qualitative agreements with the observations at both BEPC and KEK-B. Based on the detectors at Advanced Photon Source (APS), ANL, a specially-constructed detector was installed at the BEPC. It is hoped to obtain realistic values for the photoelectron (PE) and secondary electron yields as well as the energy spectrum of the electron cloud through the direct measurements of the properties of the PE cloud for both stable and unstable beams. In this paper, the experimental results at the BEPC are presented after the description of the instrumentation, and some discussions are followed afterwards.