JAERI-Conf 95-021

3a2-4
VUV ·SX High-Brillian ce Light Source
VSX Accelerator Group ·(presented by Yukihide K.AMIYA)The Institute for Solid State Physics, The University of Tokyo+KEK, The National Laboratory for High Energy Physics
JAERJ, Japan Atomic Energy Research Institute*I. Introduction
A third-generation VUV and soft X-ray ring (VSX ringin short) with a low emittance of several nm·rad is being
designed at the Institute for Solid State Physics (ISSP) of
the University of Tokyo, in close collaboration with thePhoton Factory of KEK. The proposal for constructing
the light source facility (VSX Light Source) is now in
preparation for submission to the government. This
project was previously considered as one of the whole
future plans of ISSP that will move to a new site called
Kashiwa Campus. However, it is now proposed that thelight source facility should be constructed by a newly
organized body, the Center of Accelerator Science, which
directly belongs to the university: the new center isexpected to be established soon, probably within a year
(see Fig. 1). Following a recommendation on synchrotron
radiation science made last June by the Accelerator Science
Subcommittee of the Minister of Education and Science,the establishment of the new center is aimed to obtain full
support for the construction of the VSX Light Source fromall through the university and to make up its own firmbase of the necessary manpower and budget for the facility
construction, the administration and so forth. The center isalso aimed to concentrate the university's efforts of otheraccelerator related sciences; synchrotron radiation science of
X-ray region, a cyclotron facility for nuclear study and afacility for utilizing various low-energy ion beams.

Light Source and what to study there, and also take part inthe construction of the facility, specifically theconstruction of the beamlines and their operation; it isotherwise impossible for the in-house staff to construct andoperate about thirty beamlines available at the facility.
After the construction completed, this users group becomesa central body of the user community of VSX Light
Source. Furthermore, an official committee, the Advisory
Committee of VSX Project, has been established at ISSP
(see Fig. 2): the committee is a decision-making body ofthe project, and it coordinates two Users Groups and gives
advice and recommendation to the construction groups. Itwill be a steering committee of the facility in future.
Three working groups, accelerator, beamline and researchgroups, which are presently the driving forces of theproject, is being reorganized as three construction groups
under the Advisory Committee. Meanwhile, the Positron
Users Group with active researchers of Tokyo University,
who have expressed much interest in utilizing slow
positron beam produced by the facility, is being involvedin the project.

ITokyo University II
Kashiwa campusl The Center of Accelerator Science II
Facility ofVSX Light SourceI
Other facilities

for accelerator
related ScienceFig. I New organization
The SR (Synchrotron Radiation) Users Group of Tokyo
University organized a few years before has set a working
group in order to discuss the scientific opportunities
provided by the extremely high-brilliant VSX Light
Source, and to explore potential users and then get new
proposals from these users as well as from the alreadyactive X-ray users. In addition, a new nationwide users
group (VSX Users Group), in which several hundred
people arc expected to participate, will be established thisSeptember. The users group will discuss how to use VSXFig. 1 Users groups and the committee of the project
The accelerator scheme of the VSX project consists of alinac, booster synchrotron and storage ring. The storage
ring has an energy of 2 GeV, a circumference of about 388
m, an emittance of less than 5 nm·rad, four 12.5 m longstraight sections fmd twelve 7 m semi-long straightsections. Each of 12.5 m long straight sections is aimed
to install a longer undulator, or a few kinds of undulators
which may produce synchrotron light with different
polarities and/or wavelengths. The conceptual design
report of the VSX accelerators is now in preparation.

II. Facility
Figure 3 shows a layout of the facility buildings: LightSource Building, High-voltage Power Station, Utility
Center, Power Supply Station, Assembly Hall and Office
Building. The large building at the center of the figure isthe Light Source building that houses the injectors (Linac-425-JAERI-Conf 95-021

and Synchrotron), Storage Ring, Control Room,Experimental Hall and so on. Storage Ring is at groundlevel, while Synchrotron and Linac are underground andControl Room is on a second floor, The Experimental
Hall is surrounded by a large hall called Hall for SpecialExperiments, Experimental Preparation Rooms (first floor)and Users Offices (second floor). A general construction
company and a large construction design company havebeen already involved in the design work of the facility
buildings and their utilities. The basic design of buildings
will be completed early next year.

f...

HI~

IfI
II

Table I. PrinCipal parameters of Storage Ring
Energy E [GeV]
Lattice type
Superperiod N8
Circumference C [m]7-m straight section
12.5-m straight section
Natural emittance exo [nm·rad]
Energy spread oJE
Momentum compaction aHorizontal tune Vx
Vertical tune vy ·Horizontal natural chromaticity !;xVertical natural chromaticity !;yHorizontal damping time 'tx [msec]
Vertical damping time 'ty [msec)
Longitudinal damping time 'te [msec]
Revolution frequency fr evlMHz]
RF voltage VRF [MY]RF frequency fRJ'" [MHz]j I Harmonic number ho
Synchrotron tune v8;1:!1 .! Bunch length Oz [mm]RF-bucket height (~E/E)

2.0
DBA
4

388.45124

4.78
6.66x1o-4
6.87x1o-4
18.29
9.66
-48.27-29.64
24.17
24.25
12.14
0.77181.4
500.1
648
0.007
4.00.028~riFig. 3 Layout of the facility

III. Storage Ring & Injectors
The 2 GeV Storage Ring has a lattice type of DBA andfour superpcriods with sixteen cells. The betatron anddispersion functions in a superpcriod are shown in Fig. 4.
The principal parameters of Storage Ring are listed inTables I. The chromaticity will be corrected by six
families of sextupole: two of them are put in dispersion
sections (four chromatic sextupoles in a cell), and two in
dispersionless semi-long straight sections, the remaining
two in long straight sections (four harmonic sextupoles ina straight section). Figure 5 shows a typical example ofhorizontal and vertical dynamic apertures versus
momentum deviation in a case without magnet errors. Awide momentum aperture is required to obtain a long
Touschek lifetime.
Gas-scattering and Touschek effects are sever factors ofdetermining the beam lifetime for a third-generationsynchrotron light source. The vacuum pressure less than 1nTorr is a design goal to be attained at a maximum beam
current of 400 rnA and the design value of the minimumgap of vacuum ·chamber is 16 mm at insertion devices.
Total RF voltage is about 1.4 MY in order to increase theTouschek lifetime. This value c.an be easily obtained bythree RF-cavities to be installed in Storage Ring. The
lifetimes due to gas-scattering and Touschek effects areshown in Figs. 8 and 9 of Ref. 1.

~tiD0.9].,.

...

M-426-

0.1

0.0 0

Fig. 4 Optics of a super:period~-----------------------.50

403020100~o-0--o--·o-.o-o-.o....

v~-3-o--o-/-2-1

10-o...O...-o0

230

dp/p [%]

Fig. 5 Horizontal and vertical dynamic apertures versus
momentum deviation

JAERI-Conf 95-021

generation is put in the middle of the linac. A short pulseof 1 nsec makes possible a single-bunch operation of thering. On the other hand, when the ring requires a multibunch mode of positron beam, the linac is able to deliver asemi-long positron pulse of a few tens nsec. For electron
beam, the linac can provide 800 MeV short pulse (1 nsec)
and about 250 MeV long pulse (2 f.!Sec). In addition, thisdesign of linac makes possible an option, the production ofslow positrons with a pulse length of 2 f.!Sec. The target
for slow positron production will be located at the end oflinac. When the ring is in a storage mode, the linac canprovide slow positrons for material science experiments.

The present ring design does not need C-type quadrupole
or sextupole, so that all ring magnets would be robust for
deformation caused by magnetic field or thermal load.
Almost all vacuum ducts of the ring will be made ofaluminum alloy, except for flanges, bellows and vacuum
ducts for undulators, which will be made of stainless steel.
A challenging point of the vacuum design is that in-situ
baking of vacuum ducts is not made, though they are bakedout before installation in the ring (see Figs. 10, 11 and 12of Ref. 1 for the cross-sectional views of the vacuum ducts
for bending and quadrupole magnets and undulators). For
the control system, its conceptual design has been almostfixed. The core of C~?ntrol system will consist of several
UNIX workstations. FDDI is adopted for the main data
highway and Ethernet for the branch lines. VME and VXI
is a standard of the computer interface to accelerator
components. For the undulator, the basic designs oftypical undulators, both planer and circular undulators, havebeen finished. The brilliances of synchrotron light to beobtained by some typical undulators as well as bending
magnets are shown in Fig. 13 of Ref. 1. A second- or
third-order harmonics may be utilized for higher energy
photon experiments.
For Synchrotron, the lattice design has been finished.
The extraction energy of the synchrotron is 2 GeV in order
to meet the full-energy injection to the ring. The injectionenergy is, however, variable around 300 MeV; it depends
on electrons or positrons and on the pulse length of theLinac beam. The principal parameters of Synchrotron arelisted in Table II.

Table III. Principal Parameters of the LinacElectron gun
Klystron
Number of SLED cavity
SLED output power
Accelerator guideTotal length
Maximum repetition rate
Normalized emittance (electron)
Normalized emittance (positron)

200 kV X lOA
80 MW x4
2400MW
3m x 10,2 m x 1about 60 m
50Hz
100 Jt mm·mrad
3000 Jt mm·mrad

R&D's of BPM and RF-cavity are now underway. We
have developed a BPM system that uses PIN diodes forswitching and attenuating RF-signals from pickup
electrodes. This system has already been installed in SORRING. The relative accuracy of the system obtained so far
with a real beam of SOR-RING is horizontally 0.3 f.!mrms and vertically 0.4 f.!m rms [2]. With the BPM systemdeveloped, a global orbit feedback has been applied toSOR-RING. For the horizontal feedback the orbit iscorrected by exciting the steerings and by changing the RFfrequency, while for the vertical feedback it is corrected
only by exciting the steerings. The orbit drifts have been
suppressed horizontally less than ten f.!m and verticallywithin a few f.!m; otherwise the orbit fluctuates around theorder of 100 f.!m. The examples are shown in Figs. 14 and·
15 of Ref. 1.
The R&D of Rr'-cavity is going well. The feature of
the RF-cavity is that resistive material of SiC attached toboth ends of the cavity is used for damping the HOM's.
Two model cavities were made and their low power test
was completed. The production process of SiC and themethod of welding SiC to metal have been well studied.
And further a hot model cavity that can store the sameamount of RF power as the design value or more wasfabricated last March. Presently about 100 kW RF powerhas been successfully stored in the cavity [3].

Table II. Principal Parameters of the Booster Synchrotron
0.3
Einj [GeV]
Injection Energy
2.0
Emax [GeV]Maximum Energy
4.0
frcp [Hz]Repetition Rate
97.11
C [m]
Circumfen..'llce
5.17vxHorizontal tune
4.79
"yVertical tune
0.058
aMomentum compaction
262
ExQ [nm·rad]
Natural emittance
7. Ox 1o-4
CJE/E
Energy spread-6.34l;x
Horizontal natural chromaticity-6.38l;yVertical natural chromaticity
5.48
Tx [mscc]
Horizontal damping time
5.50
'ty [mscc]
Vertical damping time
2.76
[msec]'tEtimeLongitudinal damping
0.8
VRF [MV]RF voltage
500.1
[MHz]
fRF
RF frequency
162hHarmonic number
0.024
v5
Synchrotron tune
26Oz [mm]Bunch length
0.004(t..E(E)RF-bucket height
The parameters dependent on the bCam energy are at 2 GeV.

References
Y. Kamiya et al., A Future Project of VUV and Soft
X-ray High-Brilliant Light Source in Japan, Proc. of1994 EPAC, pp. 639-641.
[2) K. Shinoe ct al., Beam Position Monitoring Systemusing PIN Diode Switches, Proc. of 1993 PAC, pp.
2295-2297.
[3] T. Koseki et al. ; High Power Test of a Damped
Cavity for lligh-Brilliant S_ynchrotron Radiation
Suurcc, in these proceedings.
[1]

Linac is about 60 m long including an ECS system: it
can provide 300 MeV positron beam together with electron
beam. This design has become only possible by adopting
the SLED scheme for RF generation and also by
incorporating recent results of R&D for high-gradientlinacs. The design parameters of Linac arc listed in Table
III. To realize the positron beam. a target of positron-427-