Brief Introduction


The Beijing Electron Positron Collider (BEPC) consists of the injector, the storage ring, the transportation line, the Beijing Spectrometer (BES), the Beijing Synchrotron Radiation Facility (BSRF) and the computer center. Below t is the general layout of the BEPC. 

1 The injector

 the injector

It is an electron position linear accelerator that can accelerate the electrons and positrons to 1.3 GeV. It is composed of the following 6 systems:

1.1 The accelerating system

It is composed of 56 accelerating tubes of disk loaded waveguide with each being 3.05 m long, 42 sets of supports for the accelerating tubes, 45 quadruple magnets, 1ns electron gun and positron converter, totaling 202 m long. It was installed in the tunnel that is 6 meters from the ground.    

1.2. The microwave power source

It consists of 16 high power klystrons and modulators, 13 sets of energy doublers, 1 power source, 1 phase control system and 1 microwave transmission line. It was installed in the 200 m long gallery on top of the tunnel.  

1.3. The vacuum system

The vacuum required by the accelerating system and the microwave system is 10-8 torr. Both in the tunnel and the gallery, there is a 200 m long vacuum pipe connecting the vacuum system. In addition, there are also vacuum pumps, vacuum valves and vacuum protection system.

1.4. The automatic control system

It exercises remote control of the parameters of various electronic apparatuses from the local station of the injector.

1.5. The beam measuring system

80 beam measuring probes of 6 kinds were placed in the injector to monitor the beam behavior.

1.6. The constant temperature water system, the ventilation system, etc.

There are constant temperature water pipe lines, water pump stations and automatic adjustment lines to ensure that the accelerating tubes and the wave guide transmission lines work under constant temperature.

2 The beam transport line

The beam transportation line is connected with the injector and the storage ring. It encompasses a 30 m long common section and the east and west section with each being 90 m long. The beam transportation line is to transport the electron positron beams output from the injector respectively to the storage ring. In the transportation line, there are 33 bending magnets, 42 quadruple magnets and 26 correcting magnets, and 78 beam measuring probes of 9 kinds, high vacuum systems, etc.. All the magnets power supplies and the control system were installed in the ground hall with the required vacuum being 10-8 torr and the installation accuracy of each part being 0.2 mm. The beams pass the transportation line without any interruption and the transportation efficiency of the electron and positron beams being 80% and 90% respectively.

3 The storage ring 

 the storage ring at BEPCII

The storage ring is a sports track shaped accelerator with a circumference of 240.4 m. It comprises the following 6 systems:

3.1. Magnets and power supplies

There are 44 bending magnets, 60 quadruple magnets, 8 high precision insertion quadruple magnets, 36 sextuple correcting magnets and 175 high current power supplies of 17 kinds.

3.2. The RF accelerating system

It consists of 4 accelerating cavities, 8 RF transmitters and the accessories. 

septum magnet

UHV & quardruple magnet

vacuum chambers in tunnel

electrostatic separator

3.3. The injector system

It contains 2 Lambertson magnets, 4 kicker magnets, 4 electrostatic separators and the power supplies.

3.4. The ultrahigh vacuum system

Its cross-section consists of 3 vacuum chambers. The circumference is 240.4 m long. There are 400 flanges. The aperture of the beam pipe is 58×120 The required vacuum is 3×10-10torr.

3.5. The beam measuring system

It is composed of 74 sets of beam measuring equipment of 9 kinds to monitor the beam behavior.

3.6. The automatic control system

The central control room of the collider contains one VAX 4500 computer, two work stations, 14 CAMAC crates, some series optic fibers, and etc. which exercises, through the local control stations, real time monitoring, display and control of the parameters of more than 900 equipment of various sub-systems and the performance parameters of the beams.

The luminosity of the BEPC at 1.55 GeV is 5×1030/cm-2.s-1,8 times that of SPEAR II. The beam energy spread reaches 0.64 MeV, half that of SPEAR II.

Synchrotron radiation is extracted from bending magnet and wiggler of the storage ring. The energy parameters of the synchrotron radiation light source when the storage ring works in a dedicated mode: beam emission at 2.2 GeV is 7.6×10-8m.rad and the current intensity is greater than 100mA. It is comparable with all the second-generation synchrotron radiation light sources running in the world.

BEPC II is a two-ring e+e- collider running in the tau-charm energy region (Ecm = 2.0-4.2 GeV), which, with a design luminosity of 1 × 1033 cm-2s-1 at the beam energy of 1.89 GeV, is an improvement of a factor of 100 over its successful predecessor, BEPC. The upgrade will use the existing tunnel, some major infrastructure items, and some of the old magnets. The 202 m long linac of the new machine can accelerate electrons and positrons up to 1.89 GeV with a positron injection rate of 50 mA/min.
Its installation was completed in the summer of 2005 and it has reached most of the design specifications. The collider consists of two 237.5 m long storage rings, one for electrons and one for positrons. They collide at the interaction point with a horizontal crossing angle of 11 mrad and a bunch spacing of 8 ns. Each ring holds 93 bunches with a beam current of 910 mA. The machine will also provide a high flux of synchrotron radiation at a beam energy of 2.5 GeV.
The manufacture of major equipment such as magnets, superconducting RF cavities (with the co-operation of the Japanese high-energy physics laboratory, KEK, and the company MELCO) and quadrupole magnets (with the co-operation of the Brookhaven National Laboratory), as well as the cryogenics system, have been completed, and their installation is under way. The pre-alignment of magnets has made good progress.

Design goals of the BEPCII

Beam energy range  1-2.1 GeV
Optimized beam energy region  1.89 GeV
Current of each beam in collision  0.93 A
Design luminosity 1 ′10 33 cm-2s-1 @189 GeV
Beam lifetime  2.7 hrs.
Injection from linac  Full energy injection: Einj = 1.55-1.89GeV


Positron injection rate >50 mA/min
Dedicated SR operation

250 mA @ 2.5 GeV