The Beijing Electron-positron Collider and Its Second Phase Construction

The Beijing Electron-Positron Collider (BEPC) was constructed for both high energy physics and synchrotron radiation researches. As an e, e collider operating in the τ-charm region and the first synchrotron radiation source in China, the machine has been well operated more than 15 years since it was put into operation. As a collider, the peak luminosity of the BEPC has reached its design goal of 5×10 cms at J/ψ energy of 1.55 GeV and 1×10 cms at 2 GeV respectively. The main parameters in the dedicated synchrotron radiation operation are: E=2.2~2.5 GeV, εx=80 nm⋅rad at 2.2 GeV, Ib=140 mA and the beam lifetime of 20~30 hours. As the second phase project of the BEPC, the BEPCII, has been approved with total budget of 640 million RMB. The construction is started in the beginning of 2004 and is scheduled to complete by the end of 2007. The BEPCII is a double ring machine with its luminosity goal of 1×10 cms at 1.89 GeV, two orders of magnitude higher than present BEPC. The BEPCII will operate in the beam energy of 1-2.1 GeV so that its physical potential in the whole τ and charm range is preserved, while the collider will be optimized at 1.89 GeV. The upgrading of the collider should also provide an improved SR performance with higher beam energy and intensity. The beam currents will be increased to 250 mA at E=2.5 GeV for the dedicated synchrotron radiation operation of the BEPCII. Some key technologies, such as superconducting RF system, low impedance vacuum devices, superconducting micro-beta quadrupoles and etc., has been intensively studied in order to achieve the target of the BEPCII.