Proceedings of LINAC 2004, Lübeck, Germany

KEKB INJECTOR LINAC AND UPGRADE FOR SUPERKEKB
S. Michizono#, for the KEK electron/positron Injector Linac and the Linac Commissioning Group,
KEK, Tsukuba, Japanlinac contributes with an advanced operational stability
for about 7,000 hours per year. Double bunch injection
and continuous injection (CI) schemes have been adopted.
The SuperKEKB project [2], aiming for a ten-times
higher luminosity, is under consideration as an upgrade of
KEKB. In this upgrade, the injector linac has to increase
the positron acceleration energy from 3.5 GeV to 8 GeV[3]. One of the plans for this upgrade is to double theacceleration field (from 20 to 40 MV/m) with a C-band(5712 MHz) rf system. The newly developed components
are summarized.

Abstract
The KEB injector linac delivers electrons and positrons
to four rings (KEKB LER, KEK HER, PF and PF-AR).
The operational status of the KEKB injector linac issummarized. The R&D work concerning diagnostics ofthe klystrons and the beam-quality are also described. An
upgrade plan of the injector linac using a C-band rf
system is under consideration for SuperKEKB. A C-band
acceleration structure was installed in the KEKB linac
after rf conditioning at more than 40 MW. An energy gainof more than 40 MV/m was confirmed by the beam
acceleration. The C-band acceleration unit has been
operated continuously for a stability test.

OPERATION STAUS OF KEKB LINAC
Operation History and Statistics

INTRODUCTION

Construction of the linac started in 1978, and operation
started in 1982. Electron/positron beams were injected to
Tristan from 1986 to 1994. The KEKB rings started theiroperations from 1998. The operation time is presently
about 7,000 hours per year. The history of the operation
time is shown in Figure 1. The accumulating operation
time reached 100,000 hours on Mar. 3, 2003. The failure
ratio has been about 5%. Figure 2 shows the injection
time delivered to 4 kinds of rings. The KEKB injection
time is more than 80% of the total injection time. The
beam-loss time is shorter than the value obtained from themachine failure in Figure 1 because many of failed
modules can be replaced by one of the stand-by modules
before beam operation. The larger beam-loss time at PF in
FY 2003 was caused by a problem of old modules in thetrigger system. It was replaced last spring.

The KEKB Injector linac has provided 8 GeV electrons
to KEKB HER and 3.5 GeV positrons to KEKB LER [1].
KEKB has recorded the highest luminosity to which the

14

2

2003

2002

2001

2000

1999

1998

1997

1996

1995

1994

1993

1992

1991

1990

1989

1988

1987

1986

1985

1984

1983

1982

4

0

0

FY

Continuous Injection (CI) Scheme

Figure 1: Operation history of the KEKB linac.
2500

1750

2000
1750
1500

1250

1250

1000

1000

750

750

500

500

250

250

0

B eam-loss time [min]1500

0
FY 1999

FY 2000

FY2001

FY 2002

FY 2003

Figure 2: Injection time and beam-loss time to PF,
PF-AR, KEKB LER and KEKB HER.

300KEKB e- Injection
KEKB e+ Injection
Dump e- Tuning
Dump e+ Tuning

200
100
0

Figure 3: Status of the beam on time. The CI scheme
started from Jan, 2004, the beam on time for LER (e+)
increased and the tuning time (Dump) decreased.

___________________________________________#

400

Oct.2003

2000

2250

Beam ON time [hours]

2250

Injectiontime [hour]

From January, 2004, the CI scheme to KEKB started
for higher luminosity operation. CI operation enables us
to increase the accumulation luminosity by about 20-

2500
KEKB-LER injection
KEKB-HER injection
PF-AR injection
PF injection
KEKB-LER beam loss
KEKB-HER beam-loss
PF-AR beam-loss
PF beam-loss

May.2004

4

1000

Apr.2004

6

2000

Mar.2004

8

3000

Feb.2004

10

4000

Jan.2004

125000

Total Operation Time [10 hour]
Machine Failure [%]6000

Dec.2003

7000

Operation Time [hour]

16

Operat ion Time [hour]
Machine Failure [%]Total Operation Time [10,000 hour]

Nov.2003

KEK Electron/ Posit ron Linac Operat ion History

8000

shinichiro.michizono@kek.jp

1Proceedings of LINAC 2004, Lübeck, Germany

30%, and it reaches about 1/fb/day. The positron andelectron beams are switched about every 10 minutes.
The injection rates at CI are 1.0 mA/s for electrons at 10
Hz and 0.5 mA/s for positrons at 10 Hz, respectively.
Figure 3 shows the beam-injection time this year. Since
the accumulated current is larger and the lifetime of thepositrons in LER is shorter than that of HER, the beamon time is longer compared with that of electrons (HER).
After CI started, it became difficult to have time for“tuning”, including beam-optics correction and/or rf
phase optimization. This tuning is now carried out on
demand.

micro-perviance2.00

Sep.,2003
Dec.,2003

1.90

M ar.,2004
M ay,2004

1.85
1.80
0

Dip Test of the Klystrons
Figure 4 shows the operation time of the klystronassemblies. Many assemblies have been used for morethan 40,000 hours. These were installed during the
KEKB construction and failures caused by the emission
decrease can become a serious problem in the near
future.

100

200
300
Time [sec.]

400

500

Figure 5: Result of the dip test. This example shows thedecrease in emission with time. Such a klystron is
replaced prior to a serious emission decrease.

20

Operation
Replaced

15
10
5
0

1
10 0
～
1
15 5
～
2
20 0
～
2
25 5
～
3
30 0
～
3
35 5
～
4
40 0
～
4
45 5
～
50

～

Figure 6: Photograph of the eight-electrodes BPM.

5～5Number of KLY assembles

1.95

In order to measure the energy spread during injection,a stripline-type BPM with eight electrodes (Figure 6) isutilized [8,9]. This BPM has also been tested as theenergy spread feedback for the electron beam and will betested for the positron beam in this year.

Operation time(×1,000 h)

Figure 4: Operation and replaced time of the klystronassemblies. The assemblies installed at the beginningof the KEKB were used for more than 40,000 hours.
In order to catch a slight indication of the emission
decrease with a limited diagnostic time (less than 10
minutes), dip tests [4] have been applied to all of the
klystrons periodically [5]. Figure 5 shows an example of a
dip test. The heater of the klystron is cut for 60 seconds
and the emission decrease is monitored. A gradualincrease in the dips with operation time is observed,
which corresponds to the emission decrease. Such a
klystron is replaced during the shutdown time or
maintenance time.

UPGRADE FOR SUPER-KEKB
Upgrade Plan

Figure 7 shows one of the upgrade plans of the KEKB
injector for SuperKEKB. Positrons with 8 GeV energy
and electron with 3.5 GeV energy are required in this plan.
The positron energy is boosted by the C-band accelerator
modules. Electron/positron injections are switched by the
kicker before the target, and both beams go throughindependent beam lines. The emittance of the positron
beam is reduced with a damping ring. Both of the 2bunches are used for positron and electron beams.

Strip Line-Type BPM with Eight Electrodes
Non-destructive procedures are required to diagnose of
the beam quality, especially at the CI scheme. The
important parameters of the beam quality are the beamenergy, beam position, energy spread and emittance.
Feedback systems for the beam energy and the beam
position are successfully operated at the KEK linac [6].
As for the beam emittance, wire-scanner measurements
have been made during injection [7]. The energy spread
had been measured using a screen monitor during thebeam dump time for linac tuning.

Figure 7: Layout of the linac upgrade for SuperKEKB.

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Proceedings of LINAC 2004, Lübeck, Germany

In this plan, twice the number of modulators should beinstalled in the C-band units. Compact modulators withinverter power supplies are adopted. Figure 8 shows aschematic layout of the rf modules.

Table 1: Operation parameters of the C-band klystron

Present Configuration ofModulator and KlystronK lystron
M odulator
40 MW
Klystron

Modulator

600R F and C oilP /SControlM odulator
C ontrol800

K lystron

Proposed Configuration

RF output
Typical charging voltage
Typical applied voltage

41 MW
42 kV
290 kV40 MW
41 kV
325 kV

Pulse duration

4 µs

2µs

An inverter power supply is a key device for a compact
modulator. A photograph of the inverter power supply isshown in Figure 10. The maximum output voltage is 50
kV with a voltage regulation of ±0.1%. Several problems,such as IGBT breakdowns, were found during operation.
Improvements of the IGBT circuits and adoption of the
durable IGBT have been applied and it runs in the
klystron gallery.

Control

560

600

C-bandInverter Power Supply

40 MW
Klystron

Modulator

S-bandBeam

Figure 8: Schematic of the configuration of modulators
and klystrons.
A C-band unit will consist of a compact modulator, aklystron, a waveguide window, a pulse compressor(SKIP) and two acceleration structures. In order todevelop this upgrade, the C-band components are being
examined. The layout of the rf system is shown in Figure
9.

RF Source

A driver klystron (100 kW) will drive eight high-power
klystrons. The existing C-band 200 kW klystron for aweather observation station (Mitsubishi ElectricCompany) is being examined by retuning. The driver
klystron (SB) can deliver more than 100 kW (at theapplied voltage of 35 kV). The same modulator and highvoltage supply as that to the existing S-band system isused.
A high-power klystron (Toshiba E3726, 50 MW, 50 pps[10]) is used to examine the rf components and to test thebeam acceleration. The existing pulse transformer (1:15)
and oil tank are reused in this experiment. The operation
conditions of a high-power klystron are compared withthe existing S-band unit in Table 1.

MAIN DRIVE LINE

C ounter

Pulse Compressor (SKIP)
A C-band pulse compressor (SKIP: SuperKEKB
Injector Pulse Compressor) was designed and tested thissummer. The specifications of the pulse compressor are
summarized in Table 2. Since the Q value decrease athigh frequency, the TE038 mode (same mode to LIPS in
CERN [11]) was chosen instead of the present TE015
mode at the C-band pulse compressor. The dimensions of
5712MHz

2856MHzCW
571 MHz

Figure 10: Photograph of the inverter power supply.
The size is 449mm(H)x 480mm(W)x 630mm(D).

Ref. Signal
Generator(FMD-30)

C-band Waveguide Driving Line
SUB-BOOSTER 3-1

SUB-BOOSTER 2

10 MHzMR

E/O

508 MHzO/E

571 MHz Optical Lines

114 MHz

Trigger
SystemDriver

30m

100m

SUB DRIVE LINE(39D)

Coax ial Lines
20m

40m
5m
SB-A

5m

30m

IΦ A

SB-1

1 kW
Amp.
System

e-

1 kW
Amp.
SystemHigh Power
ATT/PhaseS hifter

10kW
AMP.
114
M Hz
SHB1

571
MHz
SHB2

SUB DRIVE LINE(WG)

80m
SB-C

SB-B

100kW C-band
Klystron

60kW S-band
Klystron

15m

100m

IΦ A

SB3- 250MW S-band
Klystron

50MW C-band
Klystron

SLED

SLED

Sector 2

Sector 3-1

SB4- 1SB4- 2

SB5-1

SB5-2

TargetPrebuncher Buncher

ACC Guide

Sector A

Sector B

Sector C

Sector 1

ACC

e+ e-

ACC

Electron Gun

Figure 9: Rf system planned for the linac upgrade.

3

Sector 3-2

Sector 4-1 Secto r 4-2 Sector 5-1

Sector 5 -2

Proceedings of LINAC 2004, Lübeck, Germany

Figure 13: Photograph of the mix-mode window.
showed no damage, and it was installed in the klystrontest stand.

Figure 11: Photograph of SKIP.
the cavity become almost the same as that of the present
KEKB-SLED.
Figure 11 shows a photograph of the SKIP. The
maximum output power of 200 MW is obtained and thepower magnification factor is 4.7 [12]. It will be installedin the klystron gallery for long-time operation with beam
acceleration.

Dummy Load
A dummy load is designed based on the present dummyload at the S-band linac. A photograph of theTable 2: Comparison between KEKB-SLED and Cband SKIPKEKB-SLED C-band SKIP
Frequency
2856 MHz
5712 MHz
Resonance mode
TE015
TE038
Length
33.59 cm
30.72 cm
Cavity diameter
20.51 cm
23.28 cm
Qvalue (Q0)90,000130,000
Coupling
6.4
6.6
dummy load is shown in Figure 14 The load is used at the
C-band acceleration structure, and as a load of the pulse
compressor. It has been tested up to a 100 MW peak (atthe test of SKIP) and a 2 kW average.

Figure 12: C-band acceleration structure.

Acceleration Structure
The acceleration structure is designed based on thepresent S-band acceleration structure (Figure12). Highpower tests were carried out up to more than 43 MW at
the test stand [13]. During the high-power test, ananalysis of the breakdown location was carried out by rf
signals and acoustic sensors. It revealed that the input
coupler was one of the sources of the breakdown,
probably due to the thin and sharp-edged coupler iris [13].
At the second model, the coupler structure has been redesigned. A high-power test of the second model isscheduled for this September.

Figure 14: Photograph of the dummy load.

RF Window
An rf window is utilized in a waveguide system in order
to isolate the vacuum and pass rf power. A mix-mode
window [14] has been designed [15]. The calculated
electric fields at the center and the edge of the ceramics
are 20% and 50% less, respectively, compared with thepresent S-band window. The window has a sufficientband-width of more than 200 MHz (<VSWR 1.2). Figure
13 shows a photograph of the window.
In order to examine the rf window, a resonant ring has
also been designed. The resonance condition of the ring iscontrolled by the operation frequency after adjusting thetotal length roughly by spacers. The window has beentested up to 300 MW [15]. The window after operation

Figure 15: Photograph of the C-band unit installed in
the klystron gallery.

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Proceedings of LINAC 2004, Lübeck, Germany

klystrons. The eight-electrodes BPM has been tested
concerning the feedback of the beam energy spread.
An upgrade for the Super KEKB is under consideration,and the C-band components have been tested. The
acceleration structure, a pulse compressor (SKIP), has
showed the good performance at a high-power test. Other
components, such as the inverter power supply, rf window
and dummy load have also been examined, and satisfy
our specifications. Beam acceleration tests using SKIP,
and high-power tests of the second acceleration structure
are scheduled for this Autumn.
Figure 16: Photograph of the C-band acceleration
unit installed in the beam-line.

REFERENCES[1] S.Kurokawa and E.Kikutani, Nucl. Instrum. Methods
Phys. Res. A 499 (2003) 1.
[2] SuperKEKB Letter of Intent (LoI), KEK Report 044 ,August,2004, http://belle.kek.jp/superb/loi/[3] T.Kamitani, EPAC 2002, Paris, p.1088.
[4] A.S.Gilmour jr., Ch.5 of “Principles of Traveling
Wave Tube”, Arthch House INC.,1994.
[5] K.Nakao et al., Proc. of the 29th Linear Acclerator
Meeting in Japan, Aug. 2004. (in Japanese)[6] K.Furukawa, “THE PRESENT PERFORMANCEAND FUTURE UPGRADE OF THE KEKBELECTRON LINAC”, Linac2002, Gyeongju,p.380.
[7] I.Abe et al., Nucl. Instrum. Methods Phys. Res. A 499(2003) 167.
[8] T.Suwada, M.Satoh, and K.Furukawa, Phys. Rev. ST
Accel. Beams 6 (2003) 032801.
[9] M.Satoh, et al.,“Fast Data-Acquisition System for the
Beam-Energy-Spread-Monitor”, Proc. of the IX Int.
Conf. on Accelerator and Large Experimental
Physics Control System 2003, Gyeongju, p.2000.
[10] Y.Ohkubo et al.,” THE C-BAND 50MWKLYSTRONUSINGTRAVELING-WAVE
OUTPUT STRUCTURE”, Linac98, Chicago, p.932.
[11] A.Fiebig et al.,”Design Consideration, Construction
and Performance of a SLED Type Radiofrequency
Pulse Compressor using very high Q Cylindrical
Cavities” , PAC1987, Washington D.C., p.1931.
[12] T.Sugimura et al., “SKIP - a pulse compressor for
SuperKEKB Injector ", this conference.
[13] T.Kamitani et al., “Development of C-band
accelerating section for SuperKEKB”, thisconference.
[14] S.Yu.Kazakov, “A New Traveling-Wave MixedMode RF Window With a Low Electric Field in
Ceramic-Metal Brazing Area”, KEK preprint 98-140,
Aug. 1998.
[15] S.Michizono et al., “Development of C-band highpower mix-mode rf window”, this conference.
[16] S.Ohsawa et al.,”Development of C-band
Accelerator Unit for Super KEKB”, this conference.

Figure 17: Result of beam-acceleration.

Operation Status at Klystron Gallery
A C-band unit (a driver klystron, a high-power klystronwith a compact modulator, an rf window and an
acceleration structure) was installed in the klystrongallery and beam line of the linac in Aug., 2003. The firstmodel was installed into the beam line of the KEKB linac(Figures 15 and 16) in August, 2003. An acceleration
gradient of more than 40 MV/m has been achieved asshown in Figure 17. The acceleration structure has been
operated in the beam line, and it has also been confirmedthat the smaller aperture of the C-band structure does not
induce any beam characteristics. The unit has been
operated for about 6,000 hours, and breakdown statisticsof the acceleration structure and a long-time test of thecomponents have been carried out [16]. SKIP was
installed in the klystron gallery this summer, and beam
acceleration tests with SKIP and a acceleration structure
will be examined this Autumn.

SUMMARY
The KEKB linac delivers electron/positron-beams to 4
kinds of rings. The stability of the linac, where the failure
rate is less than 5%, supports an efficient operation of therings. The continuous-injection mode of the KEKB rings
requires high-quality managements of the components.
Dip tests of the klystrons are helpful to diagnose the5