PROGRESS OF 7-GeV SuperKEKB INJECTOR LINAC UPGRADE AND
COMMISSIONING
K. Furukawa∗ , F. Miyahara, M. Akemoto, D. Arakawa, Y. Arakida, H. Ego, A. Enomoto,
Y. Enomoto, S. Fukuda, Y. Funahashi, T. Higo, H. Honma, N. Iida, M. Ikeda, H. Kaji, K. Kakihara,
T. Kamitani, H. Katagiri, M. Kawamura, M. Kurashina, S. Matsumoto, T. Matsumoto,
H. Matsushita, S. Michizono, K. Mikawa, T. Miura, H. Nakajima, K. Nakao, T. Natsui, M. Nishida,Y. Ogawa, Y. Ohnishi, S. Ohsawa, F. Qiu, I. Satake, D. Satoh, M. Satoh, Y. Seimiya, A. Shirakawa,
H. Sugimoto, H. Sugimura, T. Suwada, T. Takatomi, T. Takenaka, M. Tanaka, N. Toge, Y. Yano,
K. Yokoyama, M. Yoshida, R. Zhang, X. Zhou
High Energy Accelerator Research Organization (KEK), Oho, Tsukuba, 305-0801, Japan, andSOKENDAI (The Graduate University for Advanced Studies), Oho, Tsukuba, 305-0801, Japan
Abstract
KEK injector linac is being upgraded for the SuperKEKB
project, which aims at a 40-fold increase in luminosity overthe previous project KEKB. SuperKEKB asymmetric electron and positron collider with its extremely high luminosity
requires a high current, low emittance and low energy spread
injection beam from the injector. Electron beams will begenerated by a new type of RF gun, that will inject a muchhigher beam current to correspond to a large stored beam
current and a short lifetime in the storage ring. The positronsource is another major challenge that enhances the positronbunch intensity from 1 to 4 nC by increasing the positron
capture efficiency, and the positron beam emittance is reduced by introducing a damping ring, followed by the bunch
compressor and energy compressor. The recent status of theupgrade and beam commissioning is reported.

INTRODUCTION
The electron positron injector linac at KEK has delivered electrons and positrons for particle physics and photon
science experiments since 1982. It has been rejuvenatedsince 2010 towards SuperKEKB collider, which aims at a40-times higher luminosity over the previous KEKB projectin order to increase our understanding of new physics beyond the standard model of elementary particle physics [1].
SuperKEKB asymmetric electron and positron collider with
its extremely high luminosity requires injection beams withhigh current and low emittance in transverse and longitudinal
directions [2].
Many hardware components will be installed this year inorder to deliver beams to the electron and positron accelerator complex (Fig. 1).

Figure 1: Layout of electron/positron accelerator complex.

ficiency. And a quasi-travelling wave side-coupled cavity(QTWSC) accelerates electrons with high electric field to
avoid space-charge effect. It has successfully injected thebeam into the SuperKEKB high-energy ring (HER) at about
1 nC per bunch for 10 days during the Phase-I commissioning in 2016. The beam charge is gradually increased towards
the 5-nC target in the Phase-III commissioning. The beam
charge stability is also improved to be about 3% rms.
In order to increase the availability, a new 90-degree RFgun was constructed (Fig. 2). It is equipped with a newly
designed cutdisk structure to have a larger aperture to accept a frontal laser injection, and Ir2 Ce cathode for higher
conversion efficiency (Fig. 3).
As the beam quality management is so important that
it is investigated with beam instrumentations for laser andELECTRON BEAM DEVELOPMENT
The low emittance and high charge electron beam is generated with photo-cathode RF guns. High power laser wasconstructed with an Yb-doped fiber oscillator, several stagesof fiber amplifiers and Nd:YAG thin-disk multi-pass amplifiers [3, 4]. An Ir5 Ce cathode shows stable quantum ef∗ kazuro.furukawa@kek.jp

Figure 2: Birdview of straight and 90-degree photo-cathodeRF-guns and a thermionic gun at the top.

Figure 3: Large aperture cutdisk cavity for the 90-deg gun.

the beam at several places comparing with the simulation
results [5, 6].
A thermionic gun is maintained for high-charge 10-nC
primary electron beam in order to generate positron beam.
The beam optics was analyzed and corrected at the 24-degree
merger beamline. The bending magnets will be replacedwith pulsed bending magnets to switch beams at 50 Hz as
described later.

A positron damping ring (PDR) is being constructed todamp the positron beam emittance. An energy compressor
and a bunch compressor with S-band RF power modulators will be installed on the beam transfer lines before andafter PDR in order to match the beam bunch between thelinac and the ring. Beam instrumentation and beam bunch
synchronization scheme are constructed carefully as well tooptimize the overall beam delivery performance.

Figure 6: Fabrication of a hardened FC.

POSITRON BEAM DEVELOPMENT
The high-current positron beam is generated with a 14mm thick tungsten target, a flux concentrator (FC), largeaperture S-band structures (LAS), series of solenoid magnets, and so on (Fig. 4, 5) [7]. The FC experienced a severe discharge in 2015 and the magnetic field was degraded.
A new FC was fabricated with hardening process (Fig. 6),and long-term off-line processing was performed. A retraction mechanism for the FC assembly was designed andconstructed to improve the availability.

PULSED MAGNETSIn the previous KEKB project, injection beams were pulseto-pulse modulated with moderate beam optics, and optics
matchings were performed at corresponding beam transport lines [8]. However, for SuperKEKB injection the precise beam orbit and optics management is necessary within0.1 mm in order to suppress the emittance blow-up [6].
Small form-factor (3U) power supplies were developedfor quads with advanced design of specifications of 1 mH,330 A, 340 V and 2-ms pulse width with recovery of energy
from the magnetic coils up to 75%. The same pulsed power
supplies are used to drive bending magnets to switch beams
from a thermionic gun and RF guns. Power supplies forsteering magnets were designed as well for 3mH and 10A.
Girders were also designed in-house which is ready for 0.1mm alignment in Phase-III commissioning (Fig. 7).
Those power supplies were designed with 0.5-ms flat top,
and need pre-trigger before 3 ms before the beam. Suchtiming signals can be directly generated for SuperKEKB
beams because linac and rings are tightly synchronized. It is,however, complicated to generate timing signals with a long

Figure 4: Flux concentrator assemply.

Figure 5: Positron target and a hole in front of FC and LAS.

Figure 7: Girder design with precise alignment movers.

delay for light sources, because those rings are injected on
accidental timing coincidence and those rings compensate
the circumferences changing RF frequencies. The timing
generation algorithm was developed to prepare pre-trigger
and was confirmed.
Those pulsed magnets were examined at a test stand for along term up to two months continuously in 50 Hz, and wereconfirmed to satisfy the specification of 0.1% (rms) stability(Fig. 8). They were also confirmed to operate at pulse topulse with beams in 2016. Pulsed magnets of 30 quads, 2bends and 36 steerings will be mass-produced and installed
during 5-month shutdown in 2017.

Figure 8: Two months and 50 Hz measurement of pulsed
magnet stability.

CONCLUSION
Overview of the schedule is depicted in Fig. 10. We havesuccessfully performed light source injections even during
constructions for SuperKEKB as well as the large earthquake
recovery. We will soon initiate the Phase-II commissioning with much advanced fabrications, simulations and beamstudies. Remaining equipment for SuperKEKB will be installed during 5-month long shutdown in 2017 just before
the Phase-II commissioning. While we may still face certain
challenges, they would be resolved with careful analysis.

Figure 10: Overview of the injector linac schedule.

REFERENCESSIMULTANEOUS INJECTION
Newly installed equipment and monitors are designed
to operate at 50 Hz. They will be operated through eventbased, global and synchronized controls in order to inject
beams with different properties into four separate storagerings simultaneously [8, 9].
A single injector linac would behave as four virtual accelerators operating independently with hundreds of independent
parameters modulated pulse by pulse at 50 Hz (Fig. 9). Anew beam transport line for PF-AR direct injection helps thisconcept not to interfere between PF-AR and SuperKEKB
HER, which shared the same beam transport line in the
KEKB project [10].
Event-basedControl System

F.B
e− GunF.B

PF Injectione– (2.5GeV, 0.2nC)

F.B
e− GunARC

Damping ring

SuperKEKB-LER Injection

F.B

e– (3.5GeV, 10nC)

F.B

e+ Targete+ (4GeV, 4nC)

e− GunARC

SuperKEKB-HER Injection

F.B

F.B

e– (7GeV, 5nC)
e− GunARC

PF-AR Injection[2] M. Satoh et al., “Commissioning Status of SuperKEKB Injector Linac”, in Proc. IPAC’16, Busan, Korea, May 2016,
paper THPOY027, pp. 4152–4154.
[3] X. Zhou et al., “Developing an Yb/Nd Doped Hybrid Solid
Laser of RF Gun for SuperKEKB Phase II Commissioning”,presented at Proc. IPAC’17, Copenhagen, Denmark, May2017, paper THPVA047.
[4] R. Zhang et al., “New Achievements of the Laser System for
RF-Gun at SuperKEKB Injector”, presented at Proc. IPAC’17,
Copenhagen, Denmark, May 2017, paper TUPAB056.
[5] F. Miyahara et al., “Response of Scintillating Screens to High
Charge Density Electron Beam”, presented at Proc. IPAC’17,
Copenhagen, Denmark, May 2017, paper MOPAB067.
[6] Y. Seimiya et al., “Investigation of Beam Variation and Emittance Growth Simulation with Misalignments and Beam Jitterfor SuperKEKB Injector Linac”, presented at Proc. IPAC’17,
Copenhagen, Denmark, May 2017, paper TUPAB005.

Every20 ms

ARC[1] H. Koiso et al., “Commissioning Status of High Luminosity
Collider Rings for SuperKEKB”, presented at Proc. IPAC’17,
Copenhagen, Denmark, May 2017, paper TUZB2.

F.Be– (6.5GeV, 0.2nC)

Figure 9: Single linac behaves as four virtual accelerators toinject their beams into four separate storage rings.

[7] T. Kamitani et al., “SuperKEKB Positron Source Construction Status”, in Proc. IPAC’14, Dresden, Germany, June 2014,
paper MOPRI004, pp. 579–581.
[8] K. Furukawa et al., “Pulse-to-pulse Beam Modulation andEvent-based Beam Feedback Systems at KEKB Linac”, inProc. IPAC’10, Kyoto, Japan, May 2010, paper TUOCMH01,pp. 1271–1273.
[9] H. Kaji et al., “Construction and Commissioning of EventTiming System at SuperKEKB”, in Proc. IPAC’14, Dresden,Germany, June 2014, paper TUPRI109, pp. 1829–1832.
[10] N. Higashi et al., “Construction and Commissioning of Direct
Beam Transport Line for PF-AR”, presented at Proc. IPAC’17,
Copenhagen, Denmark, May 2017, paper WEPAB044.