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13th Int. Particle Acc. Conf.
ISBN: 978-3-95450-227-1

IPAC2022, Bangkok, Thailand
JACoW Publishing
ISSN: 2673-5490
doi:10.18429/JACoW-IPAC2022-THIXSP1A NEW COMPACT 3 GeV LIGHT SOURCE IN JAPANN. Nishimori†, QST, Miyagi 980-8579, Japan
Abstract
A new 3 GeV light source with a circumference of 350
m and an MBA lattice is being constructed in north-easternJapan. Aiming at stable and high-performance operations
with an emittance of about 1 nm rad, various design and
R&D activities are being performed: the four bend
achromatic lattice using combined-function bend magnets;
the compact RF system using a TM020 mode and in-cavity
compact HOM absorbers; the in-vacuum off-axis injection
scheme enabling stored beam oscillation-free injections
with a small injection beam amplitude; the injector linac
composed of a thermionic E-gun and C-band acceleratorswith a capability of extension to feed a future soft X-ray
FEL driver, and so on. The installation of accelerator
components is ongoing. The overall design of the lightsource, R&D results, and the latest construction status arepresented.

targets under various environments. Photoemission
spectroscopy beamlines are used to measure the electronic
structure of the materials to analyze the properties ofcatalysts, battery electrodes, and so on under the operating
environment. X-ray magnetic circular dichroism beamline
employs a four-segment APPLE-II crossed undulator for
research of magnetic materials and devices [2], because
fast and versatile control of polarization is feasible byphase shifters, and higher polarization up to 0.6 is obtainedwith four segments [3]. In addition, the generation ofhigher harmonic circular polarization is feasible by using
high flux higher harmonic linear polarized light from
APPLE-II.

INTRODUCTION
A new 3 GeV light source named NanoTerasu is underconstruction in Sendai, Japan [1]. The concepts of the lightsource are to build a highly brilliant compact soft X-ray(SX) source based on reliable and proven SPring-8 /SACLA accelerator technology, to be a complementary
partner of SPring-8 to mainly cover the SX region, and toprovide SX free-electron laser (SXFEL) in the future
upgrade. The brilliance of the 3 GeV light source as afunction of photon energy is represented by solid curves inFig. 1 and those of SPring-8 by dotted curves. The main
targets of NanoTerasu are EUV, SX and Tender X-ray
regions where the brilliance is one to two orders ofmagnitudes higher than SPring-8. The target brilliance is1021 photons/sec/mm2/mrad2/0.1% b.w. and coherent ratioof roughly 10 % for several keV photon energies. A multipole wiggler (MPW) serves as a hard X-ray source insteadof a bending magnet. The above requirements can besatisfied with a beam energy of 3 GeV, stored current of
400 mA and horizontal beam emittance of 1 nm rad.
The initial portfolio of the first phase 10 beamlines underpreparation was selected to meet the effective use of thelow-emittance light source, needs of both academia andindustry, and the complementary capability of other SR
facilities in Japan. As shown in Fig. 2, there are two
EUV/SX beamlines represented by orange, four SX bygreen, three Tender-X by purple and one HX by deep blue.
Polarization dependence in soft X-ray spectroscopy
allows the investigation of electronic states in materials. In
EUV/SX region, polarization is controlled by insertion
devices such as APPLE-II because of the lack of polarizers.
Resonant inelastic X-ray scattering will be used to probe
charge, magnetic and orbital degrees of freedom on
selected atomic species of various solid, liquid, and gas___________________________________________†nishimori.nobuyuki@qst.go.jp

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Figure 1: Brilliance as a function of photon energy.

Figure 2: Layout of the 3GeV light source NanoTerasu.
In vacuum undulators (IVUs) and MPWs will be used as
tender and hard X light sources above 2 keV. Hard X-ray
photoemission spectroscopy and X-ray absorption finestructure (XAFS) will be used to investigate bulk
MC2: Photon Sources and Electron Accelerators
A05: Synchrotron Radiation Facilities

IPAC2022, Bangkok, Thailand
JACoW Publishing
ISSN: 2673-5490
doi:10.18429/JACoW-IPAC2022-THIXSP1electronic and geometric structures under operando
conditions.
Coherent
diffraction
imagingandptychography will be used to visualize the spatial
distribution of electron density and lattice distortion of asample at mesoscale.
High intensity X-rays with a continuous spectrum from
MPW are used for small-angle X-ray scattering and XAFS
to obtain information on the chemical state and structure aswell as X-ray multiscale structure analysis.

ACCELERATOR SYSTEM
The accelerator complex of the new 3 GeV facility iscomposed of a compact storage ring with a circumferenceof 350 m and a compact 110 m injector linac. The design
details are described in Refs. [1,4]. A 4-bend achromat(4BA) lattice with 16 cells is chosen for the ring to achieve
the low emittance. The lattice functions of NanoTerasu areshown in Figure 3. The red and blue curves are horizontal
and vertical β-functions and the green curve is dispersion
function. Four combined-function bends, 10 quadrupoles
and 10 sextupoles are employed in the 4BA lattice. Eightquadrupoles are used to horizontally focus the beam atbends and 4 combined-function bends and two quadrupoles
are used to vertically focus the beam. Each cell serves along straight of 5.4 m for an undulator and a short straightof 1.6 m for an MPW except for the cells assigned for beam
injection, RF cavities, and beam diagnostic instruments.

power supplies are prepared. Our concept requires a small
field deviation between mass-produced magnets.
The number and parameters of all the type of SR magnets
are listed in Table 1. The core of multipole magnets islaminated silicon steel with a thickness of 0.5 mm. The
bore diameter is 34 mm for quadrupoles and 40 mm for
sextupoles. The pole gap is 12.4 mm to obtain a highgradient. The effective length is 200 mm. The requirementof field deviation is within ±0.4%. An auxiliary power
supply is connected to an individual quad for independent
adjustment of the magnetic field. The sextupoles areequipped with auxiliary coils working as steering magnets
as well as fine-tuning of sextupole. The core type of
combined-function bend is massive steel. The crosssection is a truncated hyperbolic curve to incorporate
defocusing quadrupole and to decrease emittance. The pole
gap is 28 mm along the beam trajectory. The effective
magnetic length is 1130 mm along the arc orbit. The
requirements for dipole and quadrupole field deviations areless than 0.2 % and 0.4 %, respectively.
All the multipole magnetic fields were measured with asingle stretched wire system. The field deviations from theaverage for a family of 32 quadrupoles or 32 sextupoles arewell within 0.4 % specification. The magnetic field ofcombined-function bend is measured with a 3D Hall-probe
system. The bending field deviations from the average arewithin 0.2% and those for quadrupole are within 0.4%
satisfying requirements.
Table 1: The Number and Main Parameters of SR Magnets

Figure 3: Lattice functions of NanoTerasu.

MagnetOur concept is to build a system with a small number ofmagnet types and power supplies which results in anadvantage for mass production and low failure probabilityof power supply, that is for low cost and easy maintenance.
Figure 4 shows a lineup of magnets in one cell. The
combined-function bends are all the same. Quadrupoles are
two types, Q1 and Q3 which is designed to avoid
interference with X-ray beamlines. Sextupoles are also two
types, S1 and S4. Therefore, only five types are used as
main magnets.

Figure 4: Magnet system in each cell.
There are 11 sets of family magnets: 1 bend, 5
quadrupoles, and 5 sextupoles. Each family of magnets is
powered in series by a common power supply and 11
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A05: Synchrotron Radiation Facilities

VacuumThe vacuum system is designed to allow gas scattering
lifetime of more than 20 hours at a stored electron beam
current of 400 mA, requiring the average vacuum pressureof 1×10-7 Pa equivalent to CO. A thin stainless steel (316)chamber with 2 mm thickness and copper plating inside isemployed to meet the short magnet gap of our 4BA lattice
and to reduce resistive wall impedance. The shortest gap ofmultipole magnets and the height of vacuum chambers are
12.4 mm and 10 mm, respectively, and the clearance
between magnet and chamber is 1.2 mm, as shown in
Figure 5.

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13th Int. Particle Acc. Conf.
ISBN: 978-3-95450-227-1

Content from this work may be used under the terms of the CC BY 4.0 licence (© 2022). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

13th Int. Particle Acc. Conf.
ISBN: 978-3-95450-227-1

IPAC2022, Bangkok, Thailand
JACoW Publishing
ISSN: 2673-5490
doi:10.18429/JACoW-IPAC2022-THIXSP1Figure 5: Cross section of a vacuum chamber in aquadrupole magnet.
Discretely arranged 10 photon absorbers, 2 crotch
absorbers, and 4 supplemental absorbers together withvacuum pumps nearby are used to absorb SR from bending
magnets and to localize and evacuate photon stimulated
desorption (PSD) gas effectively. The absorbers are placed
at 17 or 29 mm apart from the electron beam trajectory. The
vacuum chambers are therefore horizontally compact aswell as magnets. Only 4 types of photon absorbers aredesigned and manufactured for low cost and easy
maintenance. They are one for absorbers (AB), two forcrotch absorbers for undulator and MPW, and one forsupplemental absorbers (SAB). Absorbers and crotch
absorbers are made of GLIDCOP and SABs are made ofoxygen free copper. The maximum SR peak power density
on absorbers is estimated to be about 200 W/mm2. The
vacuum pressure distribution in a unit cell at 400 mA
operation after 1500 Ah conditioning is calculated and theaverage pressure of CO is estimated to be 6 × 10-8 Pa
corresponding to the gas scattering lifetime of about 22
hours.
A stored electron beam needs to be dumped in acontrolled way during beam abort, which is initiated by RF
power off. The beam loses energy turn-by-turn andeventually hits vacuum chambers. To avoid vacuum
incidents, an elaborately prepared electron beam absorberis installed in every cell for the high-density beam to be
spread out before striking chambers.
A vertical beam shaker with a frequency close to verticalbetatron tune is employed to decrease the beam verticaldensity by 300 [5-7]. Graphite beam absorbers, the surfaceof which sticks out by 5 mm from the inside of the vacuum
chambers, are installed where dispersion function is
maximum and the ring tunnel wall is most distant from thechambers. That is the chamber near 8-th quadrupole in
Figure 4.

RF
The radiation loss per turn in NanoTerasu is estimated tobe 1.26 MeV where 0.62 MeV is lost in bends and the rest
is lost in insertion devices. An RF power of 500 kW is thus
required for compensating the radiation loss of a 400 mA
beam. To make the beam lifetime longer than 10 hours, an
RF accelerating voltage of 3.6 MV is required. We install
4 sets of 509 MHz acceleration cavities on one of 5.4 m
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long straight sections. A new type of compact TM020mode normal conducting cavity has been developed toaccommodate the space limitation [8]. The TM020 cavity
has nodes of the magnetic field at the fundamental mode
inside the cavity. We prepared slots along the nodes andinstalled ferrite to damp higher-order modes (HOMs)
entering the slots, because those HOMs excited in thecavity cause coupled-bunch instability. HOMs are
dissipated on the ferrite dampers while the fundamental
mode is not damped.
The shunt impedance of the new cavity is estimated to be
6.8 MΩ and RF power of 120 kW per cavity is required for
0.9 MV acceleration, which corresponds to 3.6 MV
acceleration and 480 kW RF power per four total cavities.
The klystron RF power of 1 MW is thus required for 400
mA stored beam operation.
We performed high power test of a TM020-mode cavity
and 120 kW power was successfully fed into the cavity
equipped with 12 HOM absorbers with a vacuum pressureof 1.5×10-6 Pa.

Ring Beam Injection
An in-vacuum windowless off-axis beam injection
system from the ring inside is employed for stable andtransparent beam injection together with the capability of
top-up operation [9]. The injection system consists of awindowless beam transport, two DC septum magnets, anin-vacuum pulse septum magnet, and a pair of twin kickers
having identical magnet characteristics. The system allows
a small oscillation amplitude of injected electron beam ofaround 7.5 mm and stored beam oscillation amplitude lessthan 10 μm satisfying transparent beam injection during
the top-up operation. A differential pump-system upstream
DC septa separates the ring vacuum from beam transport.
The bumped beam trajectory is 7.5 mm apart from thestored beam and the injected beam is located 7.5 mm fromthe bumped beam. The septum wall of thickness 1 mm islocated 2.5 mm from the bumped beam and 4 mm from theinjected beam. The length and kick angle of each kicker are
300 mm and 6 mrad, respectively, those of pulse septum
are 500 mm and 70 mrad, and those of DC septum are 400
mm and 48 mrad.
Twin kickers are driven by a single solid state pulser togenerate identical kicker magnetic pulses [10]. The pulser
consists of a charging circuit up to 55 kV, a main capacitorof 65 nF and a fast IGBT switch to provide peak current of
1.6 kA and half-sine pulse width of 3 μs. The fluctuation of
the charging voltage is measured to be 0.01 %, indicating
good reproducibility. The magnetic property of the kicker,
such as inductance, should be identical with another kicker[11]. We measured the inductance as a function of
frequency and the difference is found to be less than 0.2 %up to 1 MHz, which can be corrected with a variableinductor of the pulser. The difference between measured
temporal profiles of magnetic fields of twin kickers isdemonstrated to be ± 0.1 % satisfying specification.
Ceramic vacuum chambers with uniform titanium (Ti)coating with 3μm thickness are used. The magnetic field is
attenuated by 3 % due to the eddy current in the coating
MC2: Photon Sources and Electron Accelerators
A05: Synchrotron Radiation Facilities

IPAC2022, Bangkok, Thailand
JACoW Publishing
ISSN: 2673-5490
doi:10.18429/JACoW-IPAC2022-THIXSP1and the attenuation will be compensated by increasing thepower supply output. Ceramic chambers with patterned
inner Ti-coating to reduce the eddy current is underdevelopment.
The in-vacuum pulse septum has a thin septum wall witha thickness of 0.5 mm for stored and injected beams to getcloser for small injected-beam oscillation amplitude. The
magnet gap is 2 mm which is narrow enough to provide
1.4 T pulsed magnetic field uniformly along the horizontal
axis over 4 mm. The stray field integral outside of the
septum goes down to 10-5 Tm or less by using a permalloy
magnetic shield. The vacuum pressure is measured to beless than 3×10-8 Pa. We measured the pulsed magnetic field
as a function of horizontal position with a thin search coil.
The field is almost flat within ±0.2 % from 2 mm to 5 mmfrom the septum wall, where the injected beam passes.

Injector Linac
A compact full-energy injector capable of driving
SXFEL in the future is employed. A high gradient C-band
disk-loaded traveling-wave-type accelerating cavity with a
42 MV/m gradient [12], which is modified from theoriginal choke mode type cavity developed at SACLA [13],is employed to achieve 3 GeV full energy acceleration.
Twenty units of the C-band accelerator system are installedin the linac tunnel. The unit consists of two C-band 2 mlong-cavities fed by a 50 MW pulsed klystron. Each
klystron is driven with 350 kV, 310 A pulse power supplied
by a modulator, and 300 W RF input supplied by a driver
amplifier. The RF output power from the klystron iscompressed by an RF pulse compressor (SLED) by a factorof 4 to supply 80 MW peak power to each accelerator
cavity.
A newly developed 500 kV electron gun consisting of a
50 kV DC gun equipped with a commercially available
gridded thermionic cathode (CPI Y845) and a 238 MHz RF
accelerator cavity is employed [14,15]. While theemittance is believed to be deteriorated by a grid effect, it
is demonstrated that a low emittance beam can begenerated in a transparent grid scheme where the grid
potential is matched to the potential formed by cathode
anode voltage as if no grid exists. We measured the beam
current, bunch charge and normalized emittance as afunction of grid voltage and found the emittance isminimum when the transparent grid scheme is satisfied[16]. The measured minimum normalized emittance for acore part which represents 60 % of a 1 nC electron bunchis 1.5 μmrad making the transparent-gridded thermionicgun an electron source for an SXFEL.

installed in the linac tunnel. Many components such as SR
magnets, vacuum chambers, RF cavities, and an electron
gun are first tested at SPring-8 after production andtransported to the 3 GeV site.

StatusAll the magnets for the storage ring are assembled on thegirders in the magnet production factory. The final precisealignment for each girder is performed in the on-sitealignment area at the experimental hall, as shown in
Figure 6. A vibrating wire method (VWM) technique isemployed for the alignment of on-girder multipole magnets
with an accuracy of 50 μm for all the girders [17] and alaser tracker is used for alignment between girders andbends with an accuracy of 90 μm.
We prepared 4 temperature-controlled booths with thestability of <0.1 ℃ at the experimental hall where 4 VWM
alignments are performed at the same time as well as astock area where 24 girders corresponding to 4 cells can bestocked is also prepared at the experimental hall.
We perform VWM alignments for 6 girders
corresponding to 1 cell in a week and install them to thestorage ring tunnel and transport new 6 girders from theproduction factory. The girders are transported to thetunnel through the temporary opening of the tunnel andplaced on the two supporting pillars. Those pillars areplaced on a specially prepared flat floor surface made of
epoxy resin by self-leveling technique. The tilt of thesurface is less than 50 μm/m. No shim plate is necessary
between floor and pillar. The vibration transfer from thefloor to the girders is greatly suppressed by the surface
flatness. The radiation hardness of the epoxy resin has been
experimentally verified by Cobalt 60 source up to 1 MGy[18]. It takes 16 weeks for 16 cells alignment andinstallation in the ring tunnel.
We fabricated a vacuum chamber prototype andassembled it to the magnet system to check interferencewith magnets and other components at SPring-8. A leak test
and 150℃ baking for 20 hours followed by NEG activation
were performed for the prototype and ultimate vacuum
pressure less than 10-8 Pa satisfying the requirement was
obtained. No interference was found during the assemblyof the prototype. The mass-production of vacuum
chambers is on schedule and installation to the accelerator
tunnel begins this June.

SCHEDULE AND STATUS
Schedule
Most of the components were designed by 2019, and the
production phase started in 2020. Some of the magnets
were already installed in the storage ring tunnel. The beamcommissioning will start in 2023 and user operation isscheduled in 2024. The linac components such as C-band
accelerators were already produced and some of them were
MC2: Photon Sources and Electron Accelerators
A05: Synchrotron Radiation Facilities

THIXSP1
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13th Int. Particle Acc. Conf.
ISBN: 978-3-95450-227-1

Content from this work may be used under the terms of the CC BY 4.0 licence (© 2022). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

13th Int. Particle Acc. Conf.
ISBN: 978-3-95450-227-1

IPAC2022, Bangkok, Thailand
JACoW Publishing
ISSN: 2673-5490
doi:10.18429/JACoW-IPAC2022-THIXSP1[5] T. Hiraiwa et al., “Interpretation of Particle Motion in a
Circular Accelerator as Diffraction of Light”, presented at
IPAC’22, Bangkok, Thailand, Jun. 2022, paper WEIZSP1,
this conference.
[6] T. Hiraiwa, K. Soutome, and H. Tanaka, “Forced harmonic
oscillator interpreted as diffraction of light”, Phys. Rev. E
102, 032211 (2020).
doi: 10.1103/PhysRevE.102.032211[7] T. Hiraiwa, K. Soutome, and H. Tanaka, “Formulation ofelectron motion in a storage ring with a betatron tune
varying with time and a dipole shaker working at a constantfrequency”, Phys. Rev. Accel. Beams 24, 114001 (2021).
doi: 0.1103/PhysRevAccelBeams.24.114001[8] H. Ego, “Design of a HOM-damped RF Cavity for the
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[9] S. Takano et al., “Renovation of off-axis beam injection
scheme for next-generation photon source”, in Proc.
IPAC’19, Melbourne, Australia, May 2019, pp. 2318-2321.
doi:10.18429/JACoW-IPAC2019-WEPMP009

Figure 6: On-site alignment area for SR magnets at theexperimental hall.

SUMMARY
Our concept of a new compact 3 GeV light source ispresented. Hardware production and installation are in
progress. We will finish the installation phase and start
beam commissioning by the middle of 2023. User
operation is scheduled to start in FY2024.

ACKNOWLEDGMENTS
We would like to thank all the members of the 3 GeV
accelerator working group at QST, JASRI and RIKEN for
their contributions to the 3 GeV compact light source
project.

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