Luminosity Tuning and Operation Statistics at KEKBManabu Tanaka1,A）and Yoshihiro FunakoshiB）
A)
Mitsubishi Electric System & Service Co., Ltd
2-8-8 Umezono, Tsukuba, Ibaraki , Japan, 305-0045
B)High Energy Accelerator Research Organization （KEK）
1-1, Oho, Tsukuba, Ibaraki, Japan ,305-0801
Abstract

The KEKB B-Factory (KEKB) started a collision experiment in 1999 and achieved the design luminosity of 10
nb-1s-1 in May, 2003. We achieved 21.1 nb-1s-1 in 2009 (more than the double of the design luminosity). The
integrated luminosity surpassed 1000 fb-1 in 2009. We routinely make tuning on machine parameters related tobeam collision even during the physics experiment. The purpose of this adjustment (called “knob tuning”) is tomaintain the high luminosity by optimizing the collision parameters and to obtain an even higher luminosity. We
installed crab cavities in February, 2007. The method of luminosity tuning changed to some extent and some newtuning methods were introduced. We installed skew sextupole magnets in March, 2009 and the e+/esimultaneous injection scheme was realized. After those, the peak and integrated luminosity improved drastically.
We also describe the operation statistics.

1．Introduction

2．Injection method[1] [2]The KEKB B-Factory (KEKB)
started a collisionexperiment in 1999 and achieved the design luminosity of
10 nb-1s-1 in May, 2003. We introduced the continuous
injection scheme which enables us to do data acquisition
during the beam injection in 2004. We installed crab
cavities in February, 2007. The crab cavities are used in ausual physics operation and it was proven that they
operate very stably under the condition of the highcurrent beams. We installed skew sextupole magnets in
March, 2009 and the e+/e- simultaneous injection scheme
was realized. After those, the peak and integrated
luminosity improved drastically. Figure 1 shows thehistory of the KEKB operation.

When the beam was injected, data acquisition had been
temporarily stopped until 2003. Electrons (HER) andpositrons (LER) were injected after a physical experiment
had been done for about one hour, and data acquisition
was resumed afterwards. We introduced a continuous
injection mode (CIM) that enables the beam injection
during the data acquisition in 2004. In the CIM method
the injections of HER and LER had been switched every
about ten minutes. Afterwards, we succeeded in
shortening the switch interval greatly. We could switch atintervals of about five minutes in 2008. Afterwards, aninjection method was improved further. An HER andLER simultaneous injection (which means pulse-to-pulse
switching for linac pulse) was realized in April, 2009.
Beam injection schemes are shown in Figures 2 and 3
before and after introducing the CIM method.

Fig 1: History of the KEKB operation.
Fig 2: Before introducing the CIM method.

1E-mail: tmanabu@post.kek.jp

Keep the vertical beam size of LER at some target
value ） . The feedbacks (Easy feedback, Beam-size
feedback) for the horizontal offset are not used with the
crab cavity, since behavior of the beams to the horizontal
offset has changed. Now, we use the same method for thehorizontal offset as the feedback for the vertical offset
based on the beam-beam deflection method, which keep
the beam-beam kick at some target value.

4．Knob tuningFig 3: After introducing the CIM method.
Figure 4 shows the appearance of the present
simultaneous injection. The beam currents of HER andLER can be kept at almost constant values at any time by
the simultaneous injection. The temperature changes ofthe vacuum chambers that receive the influence of thesynchrotron radiation from the beam have become small.
The luminosity change has also become small. They areadvantageous for the luminosity tuning.

The orbit corrections of the rings are done every about
ten seconds. This system is called “Continuous Closedorbit Correction” (CCC). As for the orbit correction
around the IP, neither the correction accuracy nor the
rates of the correction are enough by CCC. Therefore, weneed the iBump system, which manipulates the orbits
around the IP at a rate of about 1Hz. In the knob tuning,
the x-y couplings and the vertical dispersion at the IP are
also tuned by making orbit bumps at the positions of
sextupole magnets. When we changed these knobs, theorbits around the rings are distorted. Then we halt thedata acquisition for the luminosity tuning until the orbits
become stable. In the usual tuning, several setting values
are tried for each knob looking for a better performance.
Usually, we set each knob at the value which gives thehighest luminosity. The best value is determined byfitting the knob set vs. luminosity curve with a parabolic
function as shown in Figure 5. Sometimes, we use
another method for the knob search called the Downhill
Simplex Method which is explained in section 4.2.

Fig 4: Appearance of the present simultaneous injection.

3．Orbit correction at collision point
We make a bump near the interaction point (IP) of
HER with steering magnets. The HER beam is made tocollide with that of LER in the best condition. Thissystem is called “iBump feedback”[3]. It is the best to
adjust the difference of the position（offset） and thedifference of the angle （crossing angle）at the IP to 0.
The offset and crossing angle in the vertical direction
were adjusted to 0 as much as possible. We do not use a
feedback for the horizontal crossing angle, because theangle is comparatively a big value (22mrad). We haveused two kinds of feedbacks for the horizontal offset.
（Easy feedback: Feedback to keep the ratio between theread value of a kick angle of a horizontal steering magnet
and the height of horizontal bump at some target valuethat is empirically determined. Beam-size feedback :Fig 5: Appearance of the knob scanning.
4.1

Tuning knobs

・iBump feedback
The target value of the horizontal offset, the verticaloffset, and the vertical crossing angle are adjusted to thebest value by the knob scanning. The scans for theseknobs are done at the beginning of the luminosity tuning.
After other tunings, the target scans are tried again.
・Coupling, vertical dispersion at the IP
The x-y couplings and the vertical dispersion are also
important tuning knobs.
・WaistThe minimum position of the vertical beta function at
the IP of each beam is adjusted.
・Betatron tune
The horizontal and vertical tunes are important tuning
items in the daily operation. An optimum set of the tunes
shifts slightly day by day. The luminosity tends toincrease with horizontal tunes closer to the half integer.
In case of LER, the lifetime of the head part of the bunchtrain, where the amount of the electron clouds smaller,
decrease when the horizontal tune is lowered toward thehalf integer. To prevent this problem, we introduced apulsed quadrupole magnet in 2007, which can raise thehorizontal tune only of the head part of the bunch train.
・Crab tilt
The x-y coupling parameters around the crab cavities are
tuned so that the vertical crab angle at the IP is corrected.
・Horizontal dispersion
The horizontal dispersion at the IP is adjusted bymaking bump orbits at sextupole magnets of eight pairs.
・Vertex point
The RF phase of LER is adjusted so that collision point
is kept at the nominal position. We can know the collision
point from the data on the vertex position sent from theBelle detector every about 5 minutes.
・Chromaticity
The chromaticities of the betatron tunes and the Twiss
parameters at the IP are tuned by using the sextupole
magnets. The main purpose of the tuning is to extend thebeam lifetime. In addition, the luminosity is also changedby the sextupole setting. The sextupole tuning is also
used to increase the luminosity.

4.2

Downhill Simplex Method

The scanning by Downhill Simplex Method (DSM)
was introduced in October, 2007. In this method, the 12
knobs of the x-y coupling and vertical dispersion at the IP
for both beams are searched simultaneously according to
the DSM algorism. Usually this search is continued until
the search converges. At KEKB, we use both the DSM
search and the single knob scan. It turned out that the
DSM search improves the luminosity more quickly than
the single knob scans when the knobs are far from theoptimum values in such a case as just after the optics
correction. However, the luminosity eventually achievedby the DSM search is not so different from that by thesingle knob scans. Usually we use the DSM search after
the optics correction. In every day’s operation we use thesingle knob scan. Sometimes, we try to do the DSM
search to minimize the vertical beam size of either beam.
The e+/e- simultaneous injection has contributed to the
speed-up of the knob search, since the beam currents
become more constant and so we can start the data taking
for the search anytime during the operation. Figure 8
shows the appearance of the knob search by DSM. Figure
9 shows a history of the knobs with DSM.

Figure 6 shows the betatron tune plot chart. Figure 7
shows the coupling and vertical dispersion adjustment
panel.

Fig 8: The appearance of the knob scanning by DSM.
Fig 6: The betatron tune plot.

Fig 9: A history of the knobs with DSM.
Fig 7: The coupling and vertical dispersion adjustment
panel.

6．Skew sextupole magnets
It has been shown by the beam-beam simulations thatthe momentum dependence of the x-y coupling at the IP
would degrade the luminosity if remaining values arelarger.[4] To correct these chromaticities of the x-y
coupling at the IP, 14 pairs of skew sextupole magnets(10 pairs for HER and 4 pairs for LER ) were installed in
March 2009. The effects of the newly installed magnets
were remarkable. The peak luminosity was increased by
15 or 17% by these magnets. The Fig.10 shows theluminosity and other related parameters on May 2nd 2009,
when the sextupole magnets were used in the beam
operation for the first time. In the single day, the peakluminosity was increased from 16.3 nb-1s-1 to 18.5 nb-1s-1
owing to the tuning using the magnets.

Operation Period
Hours

300

7000
6000
5000
4000
3000
2000
1000
0

250
200
150
100
50
0
2002

2003

2004

2005 2006
Fiscal Year

2007

2008

Hours

Days

Days

The crab cavities were installed in February, 2007. The
purpose is to realize virtually the head-on collision.
Before the crab cavities were installed, the peakluminosity 17.60/nb/s had been recorded with the
HER/LER beam currents of 1340/1662mA. After the crab
cavities were installed, the peak luminosity 16.10/nb/s
had been recorded with the HER/LER beam currents of
934/1605mA. In May 2009, the peak luminosity
21.08/nb/s was recorded with the HER/LER beam
currents of 1188/1637mA. The improvement of theluminosity was chiefly brought by the installed of skew
sextupole magnets. In addition, the increase of the HER
beam currents contributed to this. There are two reasons
why HER beam current was able to be increased. First,
the aperture was extended near the LER crab cavity by
the optics change. Second, the βｘ at the IP was loosened.

hours) in FY 2004, 162 days (3849 hours) in FY 2008
and 150 days (3551 hours) in FY 2009.

2009

Fig 11: Operation period.
The main purpose of the KEKB operation is thephysical experiment. The study for the accelerator
performance improvement has been also done (Beamtuning, Machine tuning, and Machine study). Figure 12
and 13 show the breakdown of use of KEKB operation
time in each fiscal year. In FY 2006 and 2007, a longtime was devoted to the study of crab crossing and the
portion of the physics experiment was decreased down to50%.

Others

7000
Operation Period [Hours]

5．Crab cavities

6000

Maintenance5000

Trouble4000

Beam Tuning

3000

Machine Tuning

2000
Machine Study

1000

Physics Run

0
2002

2003

2004

2005 2006 2007
Fiscal Year

2008

2009

Fig 12: The use of available time for KEKB in hours.

100%

Others90%
80%

Maintenance

70%
60%

Trouble50%
40%

Beam Tuning
Machine Tuning

30%
20%

Machine Study

10%0%Physics Run
2002 2003 2004 2005 2006 2007 2008 2009
Fiscal YearFig 10: The luminosity change on May 2nd 2009
when skew sextupole magnets were firstly used.

7．Operation statistics
KEKB has been operated for about nine months every
year. Figure 11 shows the operation days and hours ofeach fiscal year. The operation time was 275 days (6552

Fig 13: The use of available time for KEKB in
percentage.
Figure 14 shows the breakdown of the operation
statistics in FY 2008 and 2009. In these fiscal years,
almost no dedicated machine time was used for crab
crossing. However, the machine study for SuperKEKB,

which is the upgrade project of present KEKB, increased
and so the portion of the machine study is larger
compared with before the installation of the crab cavities.
We have a plan to stop the KEKB operation in the middleof 2010 and to start the work for the upgrade.
2008 Opration statistics
Trouble4%

Maintenance3%

Beam Tuning
9%9．Beam abort

Physics Run

We have a beam abort system that protects accelerator
devices from damages due to the beams. When amalfunction of accelerator device or beam loss is detected,
the beam is aborted within 100~160µs. Figure 16 shows
the frequency of the beam aborts from October, 2004 to
December, 2008.

Machine Study

Others0%Machine Tuning

Machine Tuning
2%

Beam Tuning
TroubleMachine Study
10%

after the crab cavities were installed.
The operation time of FY 2009 was about six months.
The annual integrated luminosity was 105.43 fb-1 and the
maximum peak luminosity was 21.083 nb-1s-1. The
averaged daily luminosity was 0.7 fb-1day-1.

Maintenance
OthersPhysics Run
72%

2009 Opration statistics
Trouble2%
Beam Tuning
4%
Machine Tuning
7%

HER Weekly Abort 2004/10 ～ 2008/12
RF

Maintenance2%
Others0%

Physics Run

60

Machine Study

50

Machine Study
7%

Number of aborts

Machine Tuning
Beam Tuning
TroubleMaintenance
OthersBeamLoss

EQ

Vac

Mag

Other

Not Ready

Crab

40
30
20
10

Physics Run
78%

04

04

/9
/1
1
05
/1
05
/3
05
/5
05
/7
05
/9
05
/1
1
06
/1
06
/3
06
/5
06
/7
06
/9
06
/1
1
07
/1
07
/3
07
/5
07
/7
07
/9
07
/1
1
08
/1
08
/3
08
/5
08
/7
08
/9
08
/1
1

0

Fig 14: Detailed content of operation in fiscal year
2008 and fiscal year 2009.

Date

LER Weekly Abort 2004/10 ～ 2008/12
RF

8．Integrated and peak luminosity

BeamLoss

EQ

Vac

Mag

Other

Not Ready

Crab

60

Integrated Luminosity [/fb][ /fb ]

Averaged Daily Luminosity [/fb/day][/fb/day ]

200

0.80

180

0.70

160

0.60

140
120

0.50

100

0.40

80

0.30

60

0.20

40

0.10

20
0

0.00
1999

2000

2001

2002

2003

2004 2005
Fiscal Year

2006

2007

2008

2009

Fig 15: The history of the annual integrated luminosity
and the daily averaged luminosity.
The operation time of FY 2008 was about six months.
The integrated luminosity was 101.06 fb-1 and the
maximum peak luminosity was 16.381 nb-1s-1. The
averaged daily luminosity of 0.6 fb-1day-1 is lower than
0.68 fb-1day-1 in FY 2005. However, it increased rapidly

Number of aborts

50
40
30
20
10
0
04
/9
04
/1
1
05
/1
05
/3
05
/5
05
/7
05
/9
05
/1
1
06
/1
06
/3
06
/5
06
/7
06
/9
06
/1
1
07
/1
07
/3
07
/5
07
/7
07
/9
07
/1
1
08
/1
08
/3
08
/5
08
/7
08
/9
08
/1
1

The luminosity is the important parameter in thecolliding-beam accelerator. It is important to increase
integrated luminosity for the success of the physicalexperiment. For this purpose, in addition to increasing thepeak luminosity, it is important to decrease the frequencyof the beam abort, to decrease the failure rate of themachine, and to decrease the dead time of the detector by
the beam noise. Figure 15 shows the history of the annual
integrated luminosity and the daily averaged luminosity.

Date

Fig 16: Details of abort from October, 2004 to December,
2008.
In the period from November 2004 to December 2006,
60% of HER beam aborts were caused by the beam losses
and 30% were caused by RF trips. These two kinds ofaborts account for 90% of beam aborts. In the case of
LER, 64% of aborts were caused by the beam losses and
18% were caused by RF trips. These two kinds of aborts
account for more than 80% of beam aborts.
After having installed the crab cavities, beam aborts
caused by crab cavity trips became serious. In case of
HER, 45% of beam aborts were due to the crab cavity
trips, 41% were due to the beam losses and 7% were dueto the RF trips. In case of LER, 43% of beam aborts were
due to the crab cavity trips, 30% of aborts were due to thebeam losses and 18% were due to the RF trips.
To accumulate the integrated luminosity effectively, it isimportant to decrease the frequency of the beam aborts.
We have been paying a close attention to the causes ofthe beam aborts and trying to decrease the frequency. As
for the aborts due to the crab cavity trips, the frequency
has been decreasing as aging of the cavities by the beams
advances.

10．Breakdown time
Figure 17 shows the history of the troubles in eachfiscal year. Figure 18 shows details in FY 2008. Figure
19 shows details in FY 2009.

OthersRefrigerator
LINAC
Belle
Beam Monitor
Control
Facility
SafetyRF
BT
MagnetVacuum

800
700
Time [Hours]

600
500
400
300
200
100
0
2002 2003 2004 2005 2006 2007 2008 2009
Fiscal YearFig 17 : The history of the troubles in each fiscal year.

Others19%
Vacuum25%

Refrigerator
0%
LINAC
2%
Belle
10%
Beam Monitor
1%

Magnet11%

Control
1% Safety

Facility
0%

0%

RF
24%

BT
7%

VacuumMagnetBT
RF
SafetyFacility
ControlBeam Monitor
Belle
LINAC
Refrigerator
OthersFig 18 : Trouble details in fiscal year 2008.

Belle
2%

LINAC
4%

Refrigerator
13% Others
1% Vacuum
10%

Control0%
Beam Monitor
0%
Safety0%
Facility0%

Magnet
8%

RF
27%

BT
35%

VacuumMagnetBT
RF
SafetyFacility
ControlBeam Monitor
Belle
LINAC
Refrigerator
OthersFig 19 : Trouble details in fiscal year 2009.
The breakdown time due to the troubles has been
decreasing, even if we take the decrease of the operation
time in to account. FY 2005 was an exceptional year,
when the trouble of Belle detector accounted for a large
portion. In the figure 18 and 19, the details of the troubles
in FY 2008 and FY 2009 respectively. In FY 2009, thetrouble rate of BT was exceptionally high, since several
troubles accidentally coincided in this fiscal year.

11．Summary
The luminosity has improved greatly by introducing
skew sextupole magnets. In addition, the simultaneous
injection of HER and LER was put to practical use. The

beam currents became more constant, and the knob
tuning was speeded up. The operation by using the crab
cavities was established. The total integrated luminosity
is 1018 fb-1 and the maximum peak luminosity is 21.08
nb-1s-1.

12．Acknowledgements
Our heartfelt appreciation goes to the members of
KEKB Commissioning Group who provided carefully
considered feedback and valuable comments.

13．References[1] KEKB B-Factory Design Report, KEK Report 95-7 (1995).
[2] http://kekb.jp.
[3] Y. Funakoshi, et.al., "Orbit feedback system for maintaining
an optimum beam collision" , Phys. Rev. ST Accel. Beams
10, 101001 (2007).
[4] Y. Funakoshi, et.al.," RECENT PROGRESS OF KEKB",
Proceedings of PAC07, Albuquerque, New Mexico, USA.