PRESENT STATUS OF THE KEKB B-FACTORY
H. Koiso, K. Akai, N. Akasaka, K. Ebihara, K. Egawa, A. Enomoto, J. Flanagan, H. Fukuma,
Y. Funakoshi, K. Furukawa, T. Furuya, J. Haba, S. Hiramatsu, K. Hosoyama, T. Ieiri, N. Iida,
H. Ikeda, T. Kageyama, S. Kamada, T. Kamitani, G. Katano, S. Kato, M. Kikuchi, E. Kikutani,
S. Kurokawa, M. Masuzawa, S. Matsumoto, T. Mimashi, A. Morita, T. Nakamura, H. Nakayama,
Y. Ogawa, K. Ohmi, Y. Ohnishi, S. Ohsawa, N. Ohuchi, K. Oide, K. Satoh, M. Satoh, T. Shibata,S. Stanic, M. Suetake, Y. Suetsugu, T. Sugimura, T. Suwada, M. Tawada, M. Tejima,
M. Tobiyama, S. Uno, S.S. Win∗ , N. Yamamoto, Y. Yano, M. Yoshida, M. Yoshioka,
S. Yoshimoto, F. Zimmermann† , KEK, Ibaraki, 305-0801, JapanAbstract
The KEKB B-factory is an energy-asymmetric e+edouble-ring collider at KEK. It has been operated since December 1998, and has recently marked the peak luminosityof 7.35 /nb/s which is the highest value in the history of colliders. By several improvements such as solenoid windingsin LER, new moving-chamber masks in HER, etc., the luminosity performance of KEKB has been signiﬁcantly upgraded last year. This paper mainly describes the progress
after the summer shutdown in 2001.

1 OVERVIEW
The luminosity performance of KEKB, both peak andintegrated luminosities, has been almost doubled in a year,
as shown in Fig. 1. The main beam parameters at the peakrecord are listed in Table 1, compared with those about a∗year ago. While the main optical parameters, εx , βx,y,σz , and the number of bunches were almost unchanged,
the beam-beam parameters increased as the bunch current
increased. The total beam currents are now mainly limitedby heating of the IR masks closest to the IP, due to both
HOM and synchrotron light.

Table 1: Beam Parameters of KEKB.
2002 May
2001 MayLER HER LER HER
Energy3.5
8.0
Circumference
3016
Current
1350 900
854
675
Bunches1224
1154
Curr./bunch
1.10 0.74 0.74 0.58
Spacing
2.4
2.4
Emittance εx18241824βx∗59615963βy∗0.62
0.7
0.7
0.7
Hor. Size @IP
103121103
123
Ver. Size @IP
2.7
2.7
2.6
2.6
εy /εx
6.7
4.5
5.3
4.0
Bunch Length
5.3
5.5
5.5
5.8
RF Voltage
6.5
12.0
6.0
11.0
ξx.079 .073 .065 .048
ξy.049 .042 .047 .029
Lifetime
100300133
259
Luminosity
7.35
3.84
Lum/24 hrs
387
207
Lum/7 days
2524
1302
Lum/30 days
8783
4047

GeVm
AmA
m
nm
cmcm
µm
µm
%
mm
MV

min.
/nb/s
/pb/pb/pb

2 HIGH CURRENT OPERATION
For higher current operation, several improvements weretook place after the summer shutdown in 2001:• More solenoid windings in LER to suppress the photoelectron cloud. The total length of the solenoid isshown at the bottom in Fig. 1. At present, almost allof the ﬁeld-free regions are covered with the solenoid
ﬁeld of more than 30 Gauss.
• New moving-chamber masks in HER: Heads of themasks were made by combination of Cu and Al or Ti
to avoid damaging the mask heads by a direct hit ofthe beam.
• Faster kickers for the beam abort system which enable
to shorten the abort gap from 10% to 4.6% of the circumference, thus increasing the number of bunches.
∗ visiting from NSRC, Thailand† visiting from CERN, Switzerland• Better beam abort system with loss monitors which
consist of PIN diodes.
• New abort chamber for both rings to avoid vacuum
leakage at high-current aborts.
• More cavities and the 0 and -1 mode feedback system.
• Better cooling system around the interaction point(IP).
With those improvements, the peak and the speciﬁc luminosities were improved successfully as the stored current
increased. No signiﬁcant single-beam blowup of the vertical beam size was observed in LER up to 1500 mA [1]. The
stability of the luminosity performance was also improved,
so that the luminosities were quickly recovered after a short
break for maintenance and hardware repair. At higher current, it is important to tune the transverse bunch-by-bunch
feedback system frequently for stable operation.

Figure 1: History of KEKB Luminosity.

3 OPTICAL PARAMETERSKEKB has been successfully operated with low-βy∗ optics. In order to keep a high luminosity stably, beamoptical functions are measured and corrected with an online model by SAD during daily operation[2]. Improvements in the beam-optical parameters are listed as below:• Horizontal tunes more closer to half-integer resonances [3].
• Better correction of the x-y coupling by using both (a)correction factors of skew quadrupoles and (b) verticalsymmetric bumps at −I  sextupole pairs, at the sametime.
• Better correction of the global β correction by adjusting the horizontal orbit as small as possible at strong
sextupoles, in particular in HER.
Fine control of the betatron tunes is necessary for thestable operation at close to the half-integer resonance. Ameasurement system with a gated tune-mater[4] has beendeveloped and working well as shown in Fig. 2.

4 LUMINOSITY PERFORMANCE
Figure 3 shows the improvement of the speciﬁc luminosity during this period. The ﬁrst jump was brought about
by good suppression of the electron clouds with extended
solenoid windings. The second one came from the closer
νx to the half integer, in particular in HER as shown inFig. 1.

Figure 2: Example of tune management with gated tunemater.

5 ORBIT DRIFTAs a result of the optics corrections, the golden orbits
with local bumps at sextupoles are determined. In daily
operation, the orbits are maintained by continuous closedorbit corrections in every 20 seconds. The horizontal orbits, however, gradually drift in a few days, which cause
the tune drift and may degrade the luminosity performance
as shown in Figs. 4 and 5. The horizontal drifts have notbeen suppressed even with the adjustment of the circumference by chicane in LER. On the other hand, no signiﬁcant
drifts of the vertical orbits were observed. The horizontal
drift is cured practically, by restoring the horizontal steer-µFigure 3: Improvement of speciﬁc luminosity in the regular4-bucket spacing operation.
ing magnets when the difference exceeds a criterion limit.
Figure 5: Orbit drift during the best 7 days during the best
7 days.

Figure 4: History of model tunes during the best 7 days.

6 NEAR-TERM ISSUES
To improve the injection rate of the positron beam, a 2bunch/pulse injection scheme has been developed[5]. Thismethods came into practical use in mid April and indeed
shorten the injection time by a half. To match the 2bunch injection mode, the bunch ﬁll pattern in the rings waschanged to an irregular 4-bucket spacing with 49 bucket periodicity. Although the integrated luminosity was improved
with the 2-bunch injection, the speciﬁc luminosity duringthat period was lower than the regular 4-bucket operation.
That irregular pattern also made the detector backgroundworse, so we abandoned the 2-bunch injection temporarily.
The 3.5-bucket spacing that was tried to increase the number of bunches also matches to the 2-bunch injection, butthat pattern has also achieved lower luminosity as shownin Fig. 6. The dependence of the speciﬁc luminosity on
the ﬁll pattern is now being studied intensively, and a rela-Figure 6: Speciﬁc luminosity in 3.5-bucket spacing operation.
tion to the HOM effects of the IR chamber and masks has
been suspected. After solving a problems on the data taking system of Belle, continuous injection [5] to LER will
be retried after the next summer shutdown.

7 REFERENCES[1] H. Fukuma, et.al., in theses proceedings.
[2] KEKB Preprint 2001-157.
[3] K. Oide, in theses proceedings.
[4] E. Kikutani, et.al., in theses proceedings.
[5] T. Kamitani, et.al., in theses proceedings.