Achievement of 200,000 hours of operation at
KEK 7-GeV electron 4-GeV positron injector linac
K Furukawa1,2 , M Akemoto1 , D Arakawa1 , Y Arakida1 , Y Bando2 ,H Ego1,2 , Y Enomoto1,2 , T Higo1 , H Honma1 , N Iida1,2 , K Kakihara1 ,T Kamitani1,2 , H Katagiri1 , M Kawamura1 , S Matsumoto1,2 ,T Matsumoto1,2 , H Matsushita1 , K Mikawa1 , T Miura1,2 ,F Miyahara1,2 , H Nakajima1 , T Natsui1,2 , Y Ogawa1 , S Ohsawa1 ,Y Okayasu1,2 , T Oogoe1 , M A Rehman1 , I Satake1 , M Satoh1,2 ,Y Seimiya1,2 , T Shidara1 , A Shirakawa1 , H Someya1 , T Suwada1,2 ,M Tanaka1 , D Wang1 , Y Yano1 , K Yokoyama1,2 , M Yoshida1,2 ,T Yoshimoto1,2 , R Zhang1,2 and X Zhou1,212High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, 305-0801, Japan
Graduate University for Advanced Studies (SOKENDAI), Tsukuba, Ibaraki, 305-0801, Japan

E-mail: kazuro.furukawa@kek.jp
Abstract. KEK electron positron injector LINAC initiated the injection operation into
Photon Factory (PF) light source in 1982. Since then for 39 years, it has served for multiple
projects, namely, TRISTAN, PF-AR, KEKB, and SuperKEKB. Its total operation time has
accumulated 200 thousand hours on May 7, 2020. We are extremely proud of the achievement
following continuous efforts by our seniors. The construction of the injector LINAC started
in 1978, and it was commissioned for PF with 2.5 GeV electron in 1982. In parallel, thepositron generator linac was constructed for the TRISTAN collider project. The slow positron
facility was also commissioned in 1992. After the KEKB asymmetric-energy collider project
was commissioned in 1998 with direct energy injections, the techniques such as two-bunch
acceleration and simultaneous injection were developed. As the soft structure design of the
LINAC was too weak against the great east Japan earthquake, it took three years to recover.
Then the construction and commissioning for the SuperKEKB project went on, and thesimultaneous top-up injection into four storage rings contributes to the both elementary particle
physics and photon science.

1. Introduction
In the experimental particle physics research in the 1970s, there was growing expectation for theworld-class Japanese domestic collider after the successes in the world-level theoretical research.
On the other hand, in the field of synchrotron radiation science, there were demands for theestablishment of a synchrotron radiation research institute with a dedicated accelerator. In
order to realize both of those accelerator projects, a 400-m electron linear accelerator capableof 2.5 GeV direct energy injection was constructed in 1982.
Since then, the injector had been in operation for 38 years in 2020, supporting the consecutive
accelerator projects of Photon Factory (PF), TRISTAN, KEKB, PF-AR, and SuperKEKB as

JFY 1970
1980
1990
2000
2010
2020
Exp. Energy
8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 90

Project

Injection Energy

Photon Factory

2.5 GeV

2.5 GeV

TRISTAN

2.5 GeV

32 GeV

Slow Positron

2.5 GeV - 55 MeV

0.1 - 35 keV

KEKB

8 / 3.5 GeV

8 / 3.5 GeV

PF-AR

2.5 GeV - 6.5 GeV

5 - 6.5 GeVSuperKEKB

7 / 4 GeV

7 / 4 GeV

Construct.

Injection Operation
Construct.

Injection Operation
Operation

Operation

Construct.

Injection Operation
Injection Operation
Construction

Injection

Figure 1. Electron positron accelerator projects operated by the injector LINAC with theirinjection beam energy and experimental beam energy.
depicted in Figs. 1, 2, 3 and 5. It has finally achieved 200,000 hours of operation in May 2020.
The brief operation history would be given.
2. 2.5 GeV injection for PF/TRISTANAt the time of the initial construction since 1978, several university-based accelerator facilities
had achieved research successes in Japan. It was fortunate that a new linear electron accelerator
had been built to share resources for advanced scientific research in both particle physics andsynchrotron radiation science, which were based on the accumulated experiences at universities.
The situation might be similar to recent J-PARC’s focus on both nuclear and particle physics,
as well as neutron and muon science. It seems that there are not many accelerator projects inthe world that have multiple disciplines from the beginning. Those Japanese accelerators arequite unique that deliver beams for multiple science fields.
While many researchers of synchrotron radiation research wanted the institute independent
from particle physics, the accelerator science played a role as a bridge between those two. One
hundred sixty of 2-m-long S-band traveling-wave accelerating structures with 2π/3 mode quasiconstant gradient were installed, and driven by forty 20-MW klystrons to achieve 2.5 GeVelectron and positron beams [1]. 2.5 GeV direct energy injection was made for PF and 2.5 GeVelectron positron beams from the injector were accelerated through the TRISTAN synchrotron
chain for the 32 GeV collision as depicted in Fig. 2.
When the synchrotron radiation facility, PF, was completed, there must be an enthusiastic
response to the dedicated synchrotron radiation facility that would promote research in

TRISTAN32 GeV/cAR
8 GeV/c
BT

Linac delivered:for PF: 2.5 GeV !"for TRISTAN:
2.5 GeV !"2.5 GeV !!

!!, !" Linac

PF

2.5 GeV/c

Figure 2. Injection for TRISTAN and PF.

synchrotron radiation science. The TRISTAN project also began to take the lead in high-energy
experimental physics, after Japanese theorist had contributed to the worldwide developmentof particle physics theory. It was realized recently that the specifications of the electric power
facilities built at that time secured the expansion possibility even for the fields of nuclear physics
and ultraviolet synchrotron radiation science. Such design facilitated the upgrades towards
KEKB and SuperKEKB later.
3. 8-GeV upgrade for KEKB
Since the construction of TRISTAN, a linear collider was expected as the next particle physics
experiment project. Instead of immediately promoting a large scale collider, however, theconstruction of a B Factory, KEKB, was carried out to experimentally confirm the remaining
issues of CP violation in particle theory proposed by Makoto Kobayashi and Toshihide Maskawa.
Since the injection performance was important to achieve the integral performance as a factory,
there were concerns compared to SLAC/PEP-II, which was planning the B-factory in parallel.
The direct energy injections for the asymmetric energy collider rings were realized by anenergy upgrade from 2.5 GeV to 8 GeV by introducing SLED microwave pulse compressors andadding 50% more accelerating structures that extends the length of the injector up to 700 m ina shape of a letter ‘J’ as in Fig. 3. It was a substantial and difficult construction because theinjector continued the PF injection [2, 3]. It made maximum use of the opportunities of thelongest shutdown of nine months in 1997 during the construction.
The success of the KEKB operation was largely due to the online operating environment of
the SAD beam simulation software and the EPICS control framework which were developed
during the injector commissioning period [4].
KEKB and PEP-II projects developed the friendly competition, and they compared theperformance of the accelerators in those control rooms everyday [5]. The performance of the
KEK injector was gradually improved during the project step-by-step [6].
The positron beam injection was enhanced by employing dual bunch acceleration. The
separation of two bunches was chosen to be 96 ns because of the frequency relationship between
the injector and the ring [7].
Then later, it also succeeded in continuous injection by switching the injection every several
minutes while the Belle collision detector was in operation. In 2008, the injection was further

KEKB

Belle

HER
8 GeV/cPF-AR
6.5 GeV/c!" BT

Linac delivered:for PF: 2.5 GeV !"for PF-AR: 3 GeV !"for KEKB: 8 GeV !"3.5 GeV !!

!!, !" Linac

!! BT
LER
3.5 GeV/c
PF

2.5 GeV/c

Figure 3. Injection for KEKB, PF and PF-AR.

Daily Operation Status
Red: Beam current (e–, e+)
Yellow: Collision luminosity
Green: Integrated luminosity
Pale blue: Lifetime (e–, e+)Purple: Vacuum (e–, e+)May.2000
Apr.2003
2 bunchesin a pulse

Feb.2005
Continuous
injection

Dec.2008
3-ring simultaneous top-up
injection with crab cavities

Figure 4. Progress of the daily operation during the KEKB project, with the stored beam
current in red and collision luminosity in yellow.
improved by the simultaneous top-up injection in to three storage rings except PF-AR in pulseto-pulse modulation switching beams with distinct properties every 20 ms employing event-based
control architecture [8] as in Fig. 4.
4. Slow positron and others
The injector facility usually contributes by injecting beams into the downstream storage rings.
However, there are cases where experiments are performed using direct electrons. In the pastat KEK LINAC, there have been experiments at the beam dump for a search for an axion likeparticle, beam irradiation calibration of tile fiber calorimeter detectors for the SSC project,
positron beam channeling experiments, and positron production using electron channelingradiation. As a result of the positron generation experiment, a crystal target was actuallyapplied to the positron generation for KEKB injection in 2006, and the positron generation
efficiency was successfully improved by about 25% [9].
Another ongoing project is the research experiments for material science and particle physics
by slow positrons. Between injections to the TRISTAN project slow positrons were generated
at the end of LINAC. While the experimental setup had to be moved twice due to the change inthe beam operation of the main LINAC, now a dedicated 50 MeV linac is used for slow positron
experiments sharing the same resources as the main LINAC [10]. It is valuable to produce
scientific results within the LINAC building.
5. SuperKEKB and simultaneous top-up injection
After the KEKB project was completed in 2010 the injector, whose girders were built with theconcept of a flexible structure, suffered a serious damage due to the Great East Japan Earthquake
in 2011. While light source injections were recovered in 3 months, it took three years to start theBelle II

Beam from Injector and Storage Current
SuperKEKB: 7 GeV #!
2000 mA
4 GeV #"
2800 mAPF:
2.5 GeV #!
450 mAPF-AR:
6.5 / 5.0 GeV #! 60 mA

LER
4 GeV
SuperKEKB
3 km

HER
7 GeV

PF-AR
6.5 GeV!! BT
efficiency"!, "" Highe+ generator!" BT

Injector Linac
PF
2.5 GeV

700 m

Damping
Ring

Low emittance
RF-gunFigure 5. Injection for SuperKEKB as well as PF and PF-AR.
beam test for SuperKEKB as the alignment was severely deteriorated. Actually, the alignment
requirement became much tight in order to suppress the wakefield effect in the accelerating
structure. While the light source injections were maintained even during the upgrade towards
SuperKEKB, the longest construction period of five months was secured in 2017.
The energy enhancement was the main subject for the previous KEKB injection upgrade, on
the other hand the SuperKEKB project required quality improvements of the injection beam
for the electron positron collision with the novel nano-beam scheme [11] as in Fig. 5. A beamemittance of about 20 mm.mrad was required with a charge of 4 nC per bunch. The positron
capture section was reconstructed [12] in order to increase the positron charge employing aflux concentrator pulsed solenoid, large aperture S-band structures (LASs), long DC solenoid
magnets and a hundred of quadrupole focusing magnets. A damping ring was newly constructedto damp the positron emittance. For the electron beam, a new high-current and low-emittanceRF gun was developed with an iridium-cerium photocathode and a quasi-travelling-wave sidecoupled cavity (QTWSC) [13].
More than hundred pulsed focusing and corrector magnets were newly installed [14]. Pulsed
low-level RF controls were also developed. Based on those equipment upgrades [15], thesimultaneous top-up injections for four storage rings of SuperKEKB HER, LER, PF ring and PFAR were realized in 2019, which contributed to the considerable improvement of experimental
efficiency [16].
The continuous operation of the electron-positron injector has supported the history ofadvanced research at KEK by providing beams for various projects as shown in Fig. 1.
At 8:50 a.m. on May 7, 2020, 200,000 hours of operation was accomplished as shown in
Fig. 6, since the PF injection operation started in 1982. Authors are very proud to have reachedthe milestone of 200,000 hours of operation by inheriting the operation results accumulated byour predecessors. Although no special event was held due to the effects of COVID-19, a toast
was made with morning coffee via video conference. In the statistics, the partial failure rate
indicates that a certain device has failed but the beam injection operation was still possible due
to redundancy, and the injection stop rate indicates that the failure was so serious that the beam
injection was impossible. At the beginning of each program, the failure rate increases before
understanding the equipment characteristics, but it tends to stabilize as countermeasures aretaken.

Statistics of the injector linac
8,000

8

Operation hour

7,000

7

Partial failure
Injection stop

6

5,000

5

4,000

4

3,000

3

2,000

2

1,000

1

0

Failure rate (%)

Operation (hour)

6,000

0
1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 2020

Fiscal year

Figure 6. Yearly operation hours of the injector LINAC with failure rates.
6. Conclusion
The KEK electron-positron injector LINAC has been able to achieve 200,000 hours of operation
while supporting experiments in multiple fields of photon science and particle physics.
References[1] Tanaka J 1980 Construction of the photon factory 2.5 GeV injector electron linac Nucl. Instrum. Methods
177 101–105 doi:10.1016/0029-554X(80)90537-6[2] Abe I et al 2003 The KEKB injector linac Nucl. Instrum. Methods A 499 167–190 doi:10.1016/
S0168-9002(02)01787-4[3] Akemoto M et al 2013 The KEKB injector linac Prog. Theor. Exp. Phys 2013 03A002 doi:10.1093/ptep/
ptt011[4] Flanagan J W et al 1998 A simple real-time beam tuning program for the KEKB injector linac Proc.
ICAP1998 (Monterey, USA) F-Tu09 https://www.slac.stanford.edu/xorg/icap98/papers/F-Tu09.
pdf[5] Seeman J 2008 Last year of PEP-II B-factory operation Proc. EPAC2008 (Genoa, Italy) pp 946–950
https://epaper.kek.jp/e08/papers/tuxg01.pdf[6] Furukawa K et al 2018 KEKB injection developments Proc. eeFACT2018 (Hong Kong, China) pp 121–125
doi:10.18429/JACoW-eeFACT2018-TUPAB01[7] Furukawa K et al 2001 Beam feedback systems and BPM read-out system for the two-bunch acceleration
at the KEKB linac Proc. ICALEPCS2001 (San Jose, USA) pp 266–268 https://epaper.kek.jp/ica01/
papers/WECT006.pdf[8] Furukawa K et al 2009 New event-based control system for simultaneous top-up operation at KEKB and
PF Proc. ICALEPCS2009 (Kobe, Japan) pp 765–767 https://epaper.kek.jp/icalepcs2009/papers/
thp052.pdf[9] Suwada T et al 2007 First application of a tungsten single-crystal positron source at the KEK B factory
Phys. Rev. ST Accel. Beams 10 073501 doi:10.1103/PhysRevSTAB.10.073501[10] Hyodo T et al 2018 Slow positron applications at slow positron facility of institute of materials structurescience, KEK AIP Conf. Proc. 1970 040004 doi:10.1063/1.5040216[11] Akai K, Furukawa K and Koiso H 2018 SuperKEKB collider Nucl. Instrum. Methods A 907 188–199
doi:10.1016/j.nima.2018.08.017[12] Enomoto Y et al 2021 A new flux concentrator made of Cu alloy for the SuperKEKB positron source Proc.
IPAC2021 (Campinas, Brazil) pp 2954–2956 doi:10.18429/JACoW-IPAC2021-WEPAB144

[13] Yoshida M et al 2014 Generation and acceleration of low-emittance, high-current electron beams forSuperKEKB Proc. LINAC2014 (Geneva, Switzerland) pp 21–25 https://epaper.kek.jp/LINAC2014/
papers/moiob03.pdf[14] Enomoto Y et al 2018 Pulse-to-pulse beam modulation for 4 storage rings with 64 pulsed magnets Proc.
LINAC2018 (Beijing, China) pp 609–614 doi:10.18429/JACoW-LINAC2018-WE1A06[15] Furukawa K et al 2018 Rejuvenation of 7-GeV SuperKEKB injector linac Proc. IPAC2018 (Vancouver,
Canada) pp 300–303 doi:10.18429/JACoW-IPAC2018-MOPMF073[16] Furukawa K et al 2020 Advanced acceleration mode switching for simultaneous top-up injection at KEKelectron/positron injector linac Proc. PASJ2020 (Matsuyama, Japan) pp 1–6 https://www.pasj.jp/web_
publish/pasj2020/proceedings/PDF/WEOO/WEOOP01.pdf