COMMISSIONING STATUS AND PLAN OF SUPERKEKB INJECTOR
LINAC
M. Satoh#, M. Akemoto, Y. Arakida, D. Arakawa, N. Iida, H. Iwase, A. Enomoto, Y. Enomoto, S.
Fukuda, Y. Funakoshi, K. Furukawa, T. Higo, H. Honma, M. Ikeda, K. Kakihara, S. Kazama, H.
Katagiri, T. Kamitani, H. Kaji, M. Kikuchi, M. Kurashina, H. Koiso, H. Matsushita, S. Matsumoto,T. Matsumoto, S. Michizono, K. Mikawa, T. Mimashi, T. Miura, F. Miyahara, T. Mori, A. Morita,
H. Nakajima, K. Nakao, T. Natsui, Y. Ohnishi, S. Ohsawa, Y. Ogawa, Y. Seimiya, T. Shidara, A.
Shirakawa, M. Suetake, H. Sugimoto, T. Suwada, T. Takenaka, M. Tanaka, M. Tawada, Y. Yano, K.
Yokoyama, M. Yoshida, R. Zhang, X. Zhou, KEK/ SOKENDAI, Tsukuba, Japan
D. Satoh, TITECH, Tokyo, Japanthe energy spread [6, 7].

Abstract
The SuperKEKB main ring is currently being
constructed for aiming at the peak luminosity of 8 x 1035
cm-2s-1. The electron/positron injector linac upgrade isalso going on for increasing the intensity of bunch charge
with keeping the small emittance. The key upgrade issues
are the construction of positron damping ring, a newpositron capture system, and a low emittance photocathode rf electron source. The injector linac beamcommissioning started in the October of 2013. In thispaper, we report the present status and future plan ofSuperKEKB injector commissioning.

J-ARC

Figure 1: Layout of SuperKEKB injector linac.
Table 1: Main parameters of SuperKEKB injector linac.
KEKB

INTRODUCTION
The KEKB project has successfully completed its
decade operation in the June of 2010. During the KEKB
operation, the injector linac provided the different flavorsof electron and positron beams to four independent
storage rings; KEKB e-, e+, PF, and PF-AR rings. Thelinac beam is injected into each storage ring in every timeinterval of 20 ms since the linac parameters of timing andlow level rf phase can be arbitrary controlled up to 50 Hz
for the simultaneous top-up injection of three rings except
PF-AR. For the simultaneous top-up injection, an event
based timing control system has been implemented to theinjector linac control system in the October of 2008 [1].
The achievement of simultaneous top-up injection made astrong impact on the triumph of KEKB project. It
improve the KEKB and PF stored current stabilities up to0.05% and 0.01%, respectively.
Figure 1 and Table 1 show the layout and the main
parameters of SuperKEKB injector linac, respectively.
Toward SuperKEKB project [2], the main issue is thehigh bunch charge transportation with keeping smallemittance. For increasing the positron intensity, the flux
concentrator and 10 large aperture S-band acceleratingstructures have been successfully manufactured andinstalled into the beam line [3, 4]. As a low emittance andhigh intensity electron source, we have designed andinstalled a photo-cathode rf gun cavity based on a noble
new scheme in the summer of 2013 [5]. For the new rf
gun system, a new laser system has been also built foraiming at the temporal modulation to obtain thelongitudinal square shape beam which can help to reduce___________________________________________#Corresponding author. e-mail address: masanori.satoh@kek.jp.

SuperKEKBe-e+e-e+

Beam energy (GeV)

83.5

74

Bunch charge (nC)

11 (10*)54 (10*)Normalized verticalemittance(mmmrad)

100

2100

2020

Normalized
horizontal emittance(mmmrad)

100

2100

50

100

Energy spread (%)

0.05

0.125

0.08

0.07

Bunch length (mm)

1.3

2.6

1.3

0.7

*

# of bunch withinterval of 96 ns

2Maximum beam
repetition (Hz)50

: Primary electron beam for positron production.

BEAM COMMISSIONING
Overview
The beam commissioning started in the October of2013. At the beginning phase of beam commissioning, we
mainly devoted the tuning of rf gun laser system foraiming at the high intensity bunch charge generation.

Figure 2: Bunch charge history at the several
locations of SuperKEKB injector linac.
Figure 2 shows the bunch charge history during the wholebeam commissioning period. In this figure, SP_A1_C5
means the bunch charge measured by the first beam
position monitor (BPM). SP_B7_4 and SP_R0_63 are thebunch charges measured at the entrance and exit of JARC, respectively. The bunch charge at the end of linac
corresponds to SP_58_0 in the same figure. We havealready archived the peak electron bunch charge of 5.6 nC
and 0.75 nC at the first BPM location and end of linac,respectively. The bunch charge stability is about 2.5%
during KEKB operation, however, the typical one
obtained by the current beam commissioning isapproximately 10%. It should be improve by stabilizing
the pulse-to-pulse fluctuation of laser system. Though thefinal goal is the bunch charge of 5 nC at the end of linac,
the bunch charge of 1 nC is enough for the Phase 1operation. In the next beam commissioning starting in thisJune, we will aim to obtain the stable bunch charge ofaround 1 nC together with the stable beam orbit control.

Bunch compression
The bunch length of electron beam emitted from the rf

gun is around 30 ps to mitigate the longitudinal wakefield
effect. The chicane has been constructed at the injector
section for the bunch compression from 30 ps to 10 ps.
Figures 3 (a) and (b) show the electron bunch lengths
measured by a streak camera before and after bunch
compression, respectively. The bunch length of 30 ps
before bunch compression is consistent with the laser
duration applied to the photocathode of rf gun. Figure 3(b) shows the measured bunch length with the optimized
bunch compression parameters of the magnetic fieldstrength and rf phase in the upstream of chicane. Theseresults show that the bunch compression is successfully
carried out by the chicane. Furthermore, the bunch length
will be compressed down to around 5 ps at the J-ARC for
mitigating the transvers wakefield generated in the sector
C to 5 though the isochronous optics was applied at theKEKB operation. We will evaluate the effectiveness ofthe bunch compression in reducing the emittance growth.
Its result will be reported elsewhere in the near future.

Low emittance preservation of electron beam
The final requirement of injection beam charge ofelectron and positron are 5 nC and 4 nC, respectively. The
low emittance preservation of electron beam is a crucial
issue because the high intensity electron beam should betransported to the end of linac without a damping ring.
Toward the emittance preservation at the end of linac, a
lot of simulation works are now going on [8]. For ourtarget emittances, as listed in Table 1, the target values ofcomponent alignment are less than 0.3 mm and 0.1 mm in
the standard deviations for the whole linac and eachsector of 100 m long, respectively. These values havebeen almost achieved. The result of emittance growthsimulation shows that the suitable beam orbit
manipulation can satisfy the target emittance of 20mmmrad at the end of linac [8], however the highprecision BPM is inevitably required. For this purpose, a
new BPM readout system based on VME bus has beensuccessfully designed [9]. The mass production of around
100 modules was already completed in this March. They
will be installed soon for the fine beam orbit control.
Figure 4 shows the results of emittance preservation
study at the end of sector B. The emittance was measured
Horizontal steering scan nominal: 0.9 (A)200x(a) Before bunch compression.

70

y

180

60

14050

120

40

100
8030602040

10200-3(b) After bunch compression.
Figure 3: Bunch length measured by a streak camera
before (a) and after (b) bunch compression at thechicane of injector section.

 y (mm mrad x (mm mrad 160-2-1012340

SX_A4_1 (A)Figure 4: Results of emittance preservation study at theend of sector B. The black and red filled circles are thehorizontal and vertical emittances, respectively.

100

Quad scan (Gun)xy90  mm.mrad

80
70
60
50
40

CONLUSIONS

30
20100012345

Bunch charge (nC)

Figure 5: Emittance measurement results at theinjector section by using the quadrupole scan method.
300

Wire scanner (Sector B)xy250mm.mrad

conducted by using the flux concentrator full currentoperation of 12 kA with the upgraded electricity andcooling water system. In addition, the safety assurance offlux concentrator operation is an important because wehave already experienced the cable burning andoverheated modulator problem.

200

Toward SuperKEKB operation, the injector linac beamcommissioning is now in progress since the October of2013. We have already measured the required electron
bunch charge of 5 nC at the first BPM, positron
generation, and bunch compression from 30 ps to 10 ps at
the injector section. Currently, the commissioning team isdevoting to increase the bunch charge at the end of linac
and improve the beam charge and position stability. Afterthese efforts, the low emittance preservation scheme will
be studied in detail for aiming at the beam injection toSuperKEKB main ring in the next year.

150
100

REFERENCES

50[1] Mitsuo Akemoto et al., “The KEKB injector linac”,
Prog. Theor. Exp. Phys. (2013) 03A002.

00.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Bunch charge (nC)

Figure 6: Emittance measurement results at the end ofsector B by using the multiple wire scanners.
by the multiple wire scanners. In this figure, the black andred filled circles are the horizontal and vertical emittances
as a function of excitation current to the steering magnet,respectively. We obtained also the similar results in thecase of changing the vertical steering value. From theseresults, the emittance preservation with the fine beam
orbit manipulation is feasible in the realistic beamoperation.
Figures 5 and 6 show the emittances measured at theinjector section and the end of sector B as a function ofbunch charge, respectively. The former and lattermeasurements were conducted by the quadrupole scanmethod and multiple wire scanners, respectively. Theemittance measured at the end of sector B is larger thanthat at the injector section since the measured beam size
can be enlarged in the wire scanner measurement due tothe beam position jitter. We are going to establish themethod of emittance preservation at the end of sector B
prior to one at the end of linac.

Positron beam commissioning
The positron beam with the bunch charge of 1 nC is
required for the Phase 1 operation starting the beginningof next year. We successfully observed the first positron
beam produced by the flux concentrator in the June of2014. The positron beam of 0.18 nC was produce by theprimary electron beam of 0.6 nC tough the operation
current of flux concentrator was limited by 6.4 kA due tothe shortage of electricity and cooling water. In thisautumn, the positron bam commissioning will be[2] T. Miura et al., “Progress of SuperKEKB”, TUYB1,
these proceedings, IPAC’15, Richmond, VA, USA(2015).
[3] S. Matsumoto et al., "LARGE-APERTURE
TRAVELLING-WAVE
ACCELERATORSTRUCTURE FOR POSITRON CAPTURE OF
SuperKEKB INJECTOR LINAC", in Proceedings ofIPAC2014, Dresden, Germany, May 15–20, pp.38723874 (2014).
[4] T. Kamitani et al., "SuperKEKB POSITRONSOURCECONSTRUCTIONSTATUS",
inProceedings of IPAC2014, Dresden, Germany, May
15–20, pp.579-581 (2014).
[5] T. Natsui et al., "Quasi-Traveling Wave RF Gun andBeam Commissioning for SuperKEKB", TUPJE003,
these proceedings, IPAC’15, Richmond, VA, USA(2015).
[6] R. Zhang et al., "Improvements of the Laser System
for RF-Gun at SuperKEKB Injector", TUPWA071,ibidem.
[7] R. Zhang et al., "25 Hz, Sub-mJ Ytterbium Laser
Source of RF Gun for SuperKEKB Linac",
WEPMA044, ibidem.
[8] S. Kazama et al., “Emittance Preservation inSuperKEKB Injector”, MOPWA053, ibidem.
[9] R. Ichimiya et al., “DEVELOPMENT OF HIGHPRECISION BEAM POSITION MONITORREADOUTSYSTEM
WITH
NARROW
BANDPASS FILTERS FOR THE KEKBINJECTOR
LINAC
TOWARDSTHESUPERKEKB”, in Proceedings of IBIC2013,Shanghai, China, September 16-19, pp.698-701(2013).