OPERATION STATUS OF THE BEIJING
ELECTRON- POSITRON COLLIDER
X. Yu, Y. Chen, X. Wang, IHEP, P.O. Box 918, Beijing 100039, ChinaAbstract
The Beijing Electron-Positron Collider (BEPC) serving
for both high energy physics experiments and synchrotron
radiation application has been well operated for more than
13 years since May 1989. After the luminosity upgrade
program from 1999, the performance and stability of theoperation were much improved in recent years. The peakluminosity of the BEPC has reached 5.8×1030 cm-2s-1 atJ/ψ energy of 1.55GeV and 1×1031 cm-2s-1 at ψ(2S) energyof 1.84GeV respectively. Over 50 million J/ψ events wereaccumulated in two years from Sept. 1999 and 14 million
ψ(2S) events have been taken in the last run from Sept.
2001 to June 2002. For dedicated synchrotron radiation
operation, the maximum beam current is around 120mA
with lifetime over 20~30 hours. In addition, two insertion
devices as well as new beamlines were installed in the lastsummer(2002). Besides, experimental studies for themachine development and BEPCII R&D are being carriedout. Improvement on the machine operation system andthe database is still under way. It's expected that BEPC
will continue to run stably till the mounting of BEPCII
starts. The operation and performance of BEPC will be
described in this paper in details, and also the presentation
will be offered about the operation team, organization
system etc.

1 GENERAL DESCRIPTION
The Main Parameters of the BEPC

Parameters
Unit Collision/ SR
Operation energy (E)GeV
1.0-2.8/ 2.2
Injection energy (Einj)
GeV
1.3
Circumference
m240.4B-function at IP (Bx*/By*)m
1.3/0.1//18/18
5.8/6.7/0.02//Tune (νx/ νy/ νz)mm
0.39*/0.08
Hor. emittance (εx0)
RF Frequency ( frf)
MHz199.526
Harmonic number (h)160
RF voltage (Vrf)MV
0.6-1.6/0.8
Bunch number (Nb)
1×1/60-80
Max. single beam currentmA
22*/137
Beam lifetimehrs
6-8/20-30
Peak luminosity
cm-2s-1
2.9×1030**-@1.55Gev
BEPC has been well operated nearly 14 years since
May 1989, and have obtained many important fruits bothin high energy physics experiments and synchrotron
radiation application. The leading results are as follows:* Precision Measurement of mτ* Study of ξ(2230)& q(1720)* ψ’ VP,VT* measurement of fDs* R measurement at 2 -5 GeV* Theoretical study of τ and Charm physics etc.
In synchrotron radiation application , many users comefrom the universities and the institutes all over thecountry carried out their experiments during the dedicatedbeam times every year.
The luminosity upgrade program of BEPC were
finished in the spring of 1999. We had gained primarysuccess, over 50 million J/ψ events taking from 1999 to2001. Since April 1, 2001, BES(Beijing Spectrometer)
team have also carried on the peak scan for ψ(2S),ψ(3770) and the data taking later. Machine study for
BEPC and BSRF (Beijing Synchrotron Radiation
Facility) experiments were executed. For dedicatedsynchrotron radiation operation, BEPC provide maximum
beam current is around 120mA with lifetime over 20~30
hours.
The last round operation of BEPC started in September
2001, shut down in the middle of June 2002 was planned.
Untill March 2002, BES team had been working
continuously over 4 months, and over 14 million ψ(2S)
events were accumulated. Up to May 17 2002, about
285,800 ψ(3770) events(the integrated luminosity reached8.15 pb-1) were accumulated. For dedicated synchrotron
radiation run, BEPC had operated nearly 3 months(alternation of 3 times). BSRF team with there users had
finished about 300 experiment subjects.
The latest BEPC operation began in Nov. 2002, and theplan is still the data taking for ψ(3770) as well as 3 times
dedicated BSRF experiment.

2 PERFORMANCE
Comparing with the operation of 1999/2000 and2000/2001 operation year, BEPC has made great progress
both for BES and BSRF experiments. It can be seen from
Table 1 that the collision beam current is increased, andthe injection time is reduced, so more integrated
luminosity and events are gained in 2000/2001 operation.
[1]
In the operation year of 2001/2002, BEPC held andexceeded these record, for example, the peak luminosity
is reached 12.58×1030cm-2s-1, and the maximum
integrated luminosity per shift is 288 nb-1 in the periodfor ψ(2S) data taking.

Table 1: Comparison between 00/01and 99/00 operation
1999/2000
operation

2000/2001
operation

1~2

3~430
43.4
67.8
4.5
7.9
104.7152.91252.5
72.3
4.8
10.1
118.4
212

Average rate of positron injection(mA/min)
Minimum injection time (minutes)
Maximum beamJ/ψcurrent (mA)ψ (2S)
Maximum luminosity
J/ψ
(×1030cm-2s-1)
ψ (2S)
Maximum integrated
J/ψluminosity per shift (nb-1)
ψ (2S)The BEPC runs about 9 months per year in average
including 5 months for high energy physics experiments,
3 months for dedicated synchrotron radiation running,
about one months for start-up and machine study (MD).
The operation time distribution is shown as Table 2.
Some results of the operation for BES and BSRF are asfollows.
Table 2: Operation time distribution
BES BSRF MD

Injec- CommisFault Othertion
sion

6504

2412

950

260

628

1465812574.4 1708.2 750.2 664.7

490.4

345.2

47.8

YearTotal(hrs)1999-2000
2000-2001

1481

760

1999-2000 100 (%) 37.1

22.8

11.7

14.6

4.0

9.7

0.2

2000-2001 100 (%) 39.1

26.0

11.4

10.1

7.5

5.2

0.7

It can be seen from Table 2 that the operation time forBES and BSRF are increased, and the injection and thefault time are reduced, but the commissioning and recovertime are increased.

2.1 BEPC Operation for BES
Due to significant improvement in machine performance(β function at IP was reduced from 8.5cm to 5cmetc.), the integrated luminosity per day increased by factorof 3 – 4 in recent three years operation than before.

Figure 1: Accumulated online hadron events in 20002001 operation year

Figure 2: BES data taking status in 2001-2002 year.
The BESII had collected over 50 million J/ ψ events inthe past two years (compared with the BESI 8 million J/ψ
events in about two years), and collected 14 million
ψ(2S) events in 4.6 months (compared with the BESI 3.8
million ψ(2S) events in 3 months). For ψ(3770) datataking in last May, the integrated luminosity is reached8.15 pb-1; The integrated luminosity of 45 pb-1(on line)
are planned in 2002/2003 running and the great physicalresults are expected. Figure 1 and Figure 2 shows the BES
data taking timetable in recent two years.

2.2 BEPC Operation for BSRF Experiment
Since February 2001, during the synchrotron radiation
experiment, for the first time we achieved to inject beamat fixed time of 7:00 am and 7:00 pm everyday. Between
two injections, the beam current was kept around 120-65
mA and the beam lifetime was about 20-30 hours. Afterinjection on time, the integrated beam current wasaveragely increased from 1.7Ah to 2.0Ah per shift.
Up to now, BSRF has become an important experimental platform. The users come from many units athome and abroad. They come from 46 Universities, 30Institutes of CAS, 18 Institutes of Ministries andCommissions and 6 Others. About 700 subjects carriedout their experiments during the dedicated beam times
last two years. The distribution of scientific area of users
is shown as Figure 3.

Figure 3: Scientific area of BSRF users

BSRF will construct two multi-cell wigglers(last year)
and three beamlines: macro-molecular crystallography
beam-line , XAFS beamline and medium energy x-ray
beamline (1.5-6KeV); Reconstruction 3B1B beamline,
Monochro-mators of 4W1C and 4B9A.
After all of above mentioned goals have been achieved,
the front-end will be increased from 4 to 7, the beamlines
will be reached from 9 to 12, and the experiment stations
will be expanded from 11 up to 13. The performances ofthe beamlines and experiment stations will be furtherenhanced. The research fields will be more extended.

2.3 BEPC Machine Study
There are two objectives for BEPC machine development study. One is to find out and resolve the problems aswell as some faults in time during the operation. This
includes optimization of operation mode, examination andrepair of hardware system. Experiment on the better andmore stable mode for future operation.
Another objective is to do some experimental researchon beam dynamics study both for BEPC and its upgrade
project as BEPCII.
(1) Beam Based Alignment (BBA)
Depending on beam itself, Beam Based Alignment
system aligns the difference between the magnetic centerof magnets and the electric center of BPM. Precise
measurement of the offsets will greatly improve the performance of BEPC, and the BBA system will be one of
the basic systems of BEPCII. As the first step to apply
BBA on BEPC, additional windings were added to the 32
quadrupoles during the summer shutdown in 2000 so thatthe strength of each quadrupole can be individually
adjusted within ±3% of its normal setting value. Thenexperiments as well as software development were carriedout in recent two years to measure the offset of BPMs.
With the preliminary data the quadrupole offset on BEPC
can be calibrated to less than 0.2mm. Further study toreduce the excursion of the closed orbit is underway.
(2) Experiment on Photoelectron Instability (PEI) [2]A specially-constructed detector was manufactured andinstalled at the BEPC storage ring for the electron cloudmeasurement. Joint experiments with experts from KEK
and APS have been done to obtain more information on
the photoelectron and secondary electron yields as well as
the energy spectrum of the electron cloud through thedirect measurements of the properties of the PE cloud forboth stable and unstable beams. 4 more detectors are to beinstalled on the BEPC during this summer shutdown to do
further studies. The experiment of PEI will be benefit toBEPCII.
(3) Dust effect and beam lifetime study
In the routine operation of the synchrotron radiation
mode with multi-bunches, sudden reduction of the beam
lifetime was observed. It was conjectured that this may
be due to the dust effect which comes from the vacuum
pumps. Experiment shows that with distributed ion pumps(DIP) in one half of the storage ring were switched off

while the vacuum did not drop significantly, the rate on
the sudden beam lifetime decrease reduced clearly.
(4) Commission of parasitic mode
As the increased demand from BSRF users, theparasitic mode with wigglers for SR during the highenergy physics was commissioned recently.
Other machine study includes: commissioning of large
emittance mode, single interaction point experiment andvacuum measurement with high beam current.

3 IMPROVEMENTS AND OTHER
To make so much a progresses, besides the hard workof BEPC people, following improvements were taken:
Operation with golden orbit and optimal working points:
we found the golden orbit and the optimal working points
for collision mode, with which the peak collision beam
current is increased stably higher and higher. Before
switching off the separator, we measure and adjust theworking points carefully until the optimal values are got.
The precision of spectrum analyzer is less than 1 kHz, theworking points are less than 0.001.
The improvement of linac includes:
All the power supplies of klystron were improved,
which stabilize the beam energy at the exit of linac, andare helpful to the increase of injection rate, and otherwise.
Some improvements of the storage ring are:(1) The precision of magnet alignment was improved.
During the summer shutdown, re-survey and alignment of
the magnets of the storage ring are carried on. We use
Laser Tracker firstly to survey the storage ring, which canreduce error effectively.
(2) Stability of the power supply for magnets was much
more improved. All the power supplies of the correction
magnets in the storage ring (including the transport lines)
were upgraded during summer shutdown. All the power
supplies of the dipoles and the quadrupoles in the storage
ring were calibrated before starting. The database of thebeam diagnostics system was improved and we can findout the unstable power supply in time by checking thehistory data.
(3) The temperature of the cooling water for the RF
cavity gets more stable. By modifying the control
software, updating one faster computer and a moresensitive magnetic valve, now the change of watertemperature is controlled within ±0.2°C, while which was±1°C before.
(4) A distributed beam loss monitor system based on
the CAN bus which can detect slight beam losses along
the storage ring has been constructed. This helps us tounderstand the beam loss mechanism and find thecorresponding problem [3].
The Control system
The current control system of the BEPC was built in
1987, which was transferred from SLAC New Spearsystem and upgraded in 1994. A VAX4500 computerwith the CAMAC hardware controls most of theequipment on the storage ring. Some devices arecontrolled by PCs including the beam instruments,
injection power supplies and linac equipment. Two VAX
workstations serve as the console and all of the machines
are connected with 100Mbps Ethernet. Since 1994 thecurrent system runs well.
According to the design of the BEPCII, a double ring
schema will be adopted and a number of new devices will
be added in the system, such as the super-conducting RF
cavities, and beam feedback system. So the currentsystem has to be upgraded and it will be developed withEPICS. VME IOCs will be added in the system withfield-bus, PLCs to control equipment. And we will keepsome CAMAC hardware in use and merge it into theEPICS system. Recently the development of prototype
system is in progress.

4 ORGANIZATION OF THE
OPERATION TEAM
We established the full time operation team in 2001 forpoolling the strength to jump in the design and theconstruction of BEPCII(the upgrade project of BEPC),
the organization system chart is as follows:
Deputy Director of IHEP
↓ …
Deputy Director of Accelerator Center↓ …
Head of Linac Head of the Storage Ring↓↓
10 operators
10 operators
Number of operators per shift are 4 persons, 2 persons
work at the central control room, and other 2 work at theLinac control room. The type of shift is 5-shift rotation,and the work time is 12 hrs per shift, i.e. after working on
duty 12 hrs, the operators have a rest for 48 hours.
Most of the operators are young people, the mean andmedian years of experience are less than 2 years(only as
an operator since Sep 2001), they come from the different
professional groups of the Accelerator Center such as AP,
RF, Control groups and so on. They have been working at
each group for several years(from 1 year to 10 manyyears). In general, the new hires also come from abovegroups and they graduated from the different universities.
They take charge of the operator or the chief operator bytraining 3-4 months.
The type of maintenance program of BEPC isprevention each other the combination with random
during the summer downtime and in the running time.

Almost all of the maintenance works of the machine bedone by our staff. The correlation personnel of everysystem(group) undertake each responsibility, by way of
coordinating promptly solving the problem or fixes abreakdown. The downtime of the machine yearly average
is about 25%(3 months ).
Moreover, our logbook is recording paper special
made(printed) by ourselves. The control room area isabout 85 and 100 square meter (for Linac and the centralcontrol room) and the number of display screens are about
15 to 20 respectively. The control system description is as
above third section.
The special challenges for our operation group are as
follows: The ageing phenomenon of the equipments andcomponents and parts are becoming seriously increasingly, for the operators and the maintenance personnel,
they work very hard, but the fault rate is still move
upward to some extent year after year. The second
problem is: The personnel are young and are short ofexperience, including the operators and the maintenancepersonnel.

5 SUMMARY
After the luminosity upgrade program were finished,
BEPC has been well operated for more than 3 years, andhave taken enormous success such as 50 million J/ψ
events and 14 million ψ(2S) events taking; BSRF has
become an important experimental platform; two insertion devices as well as new beamlines and the experimentstations such as the biology macro-molecular crystallography beamline and the experiment station were constructed, the research fields will be extended. Besides,
experimental studies for machine development andBEPCII R&D are being carried out. It is expected that
BEPC will continue to run stably till the installation ofBEPCII starts.

6 REFERENCES[1] X.M. Yu et al, “The Operation Status of BEPC inMeeting
2000/2001 Year ”, 6th BEPC Annual
proceedings, p.8-13.
[2] Z.Y. Guo, “Studies on the Photoelectron Cloud at theBEPC”, APAC01 proceedings, p. 377-379.
[3] J. Cao et al, “BEPC Storage Ring Beam Loss Monitor
System Design”, APAC01 proceedings, p.621-623