The lith Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Status of the New SUBARU project
New SUBARU project teampresented by Yoshihiko SHOJILASTI, Himeji Institute of Technology, 2167 Shosha, Himeji, Hyogo, 671-22 JAPANSPring-S, Kamigori, Hyogo, 687-12 JAPAN
Abstract

Table 1: Main parameters of new SUBARU storage ring.

New SUBARU project constructs an 1.5 GeV synchrotron
light source ring in the SPring-8. The ring covers the region from VUV to soft X-ray, which is complemental to theSPring-8 storage ring. The ring has invert bending magnets
with which the momentum compaction factor can be varied
from +0.0012 to -0.001. Two very long straight sections(14m each) will be used for a study and a development ofnew light sources such as FEL. The first beam commissioning is scheduled at the end of September 1998.

Fundamentals
Injection energy
Operation energy
Stored current (goal)
Circumference L
Revolution period
Harmonic No. n
RF frequency
Betatron Tunes
Chromaticity (~)

1 INTRODUCTION
New SUBARU is a name of the project to construct a fa-.
cility with an 1.5 GeV synchrotron light source ring in theSPring-8 site which uses the 1.0 GeV Linac as an injector. LASTI(Laboratory of Advanced Science and Technology for Industry) of Himeji Institute of Technology is incharge of the construction collaborating with SPring-8. Theconstruction cost of the ring is borne by the local government, Hyogo prefecture. The ring covers the photon energy region from VUV to soft X -ray, and is capable of offering hard X-ray and IR using insertion devices. This energy
region is suitable for industrial uses, such as X-ray microlithography, LIGA for micromachining, material processings, etc. Besides the ring, the facility has a PEL-dedicated
15 MeV LINAC named LEENA (Laser Enhanced ElectroNAccelerator) [1]. With these all the facility covers photon
energy region from O.leV to 50 keV. The expected brilliance and energy region is shown in Fig.l.
The ring is designed to be a complement to the 8 Ge Vstorage ring (SR). It is not a low emittance ring, but having a high flexibility of operation and then to be convenientfor R&Ds. Two main characteristics of the ring lattice are( 1) variable momentum compaction factor (a) with invert
dipoles and (2) two straight sections as long as 14m (11mis free for a insertion) each. A quasi-isochronism or controllable momentum compaction factor would be one of key
techniques of future electron synchrotron. It would supply
a short pulsed light in synchrotron light source rings, possibly high gain of ring FEL, high luminosity for colliders andlow longitudinal emittance in damping rings. An operation
with negative a is another important theme. It is thought tohave an advantage in bunch shortening because a potential
well distortion by a inductive impedance would enlarge theRF voltage gradient. The other characteristic, long straightsections, will be used for a development of new insertion
light sources such as FEL.
The mission of the project is to stimulate industrial activities and supply seeds of new technology for industries inal

1 GeV
0.5"" 1.5 GeV
500mA
118.716 m
0.396 p, sec
198
500MHz6.21/2.17-19/-7.5+0.0012"" -0.001

Parameters at
Natural emittance
Coupling
Bending field
Critical photon
Radiation loss
Damping time X/YLongitudinal
Energy spread
RF voltage
Bucket height
Synchrotron tune
Bunch length (lo-t)
Touschek life

E = 1.5GeV, a = 0.001267nm
10%1.55 T
0.53 nm = 2.33 keY
176 keY/turn
6.56/6.73 msec
3.42 msec
0.072%
250kV
0.83%
0.002227 psec> 10 hrs

the local area. The ring will be used not only to promote industrial activities but also to develop research works of newlight sources and future accelerator technology. The facility
is expected to play an important role in a big research complex including SPring-8. The construction of the ring will
be finished by the end of March 1998, including four insertions and two beam lines. The first beam commissioning ofthe ring is scheduled at the end of September 1998.

2 STORAGE RING
The ring has a race track shape with two fold symmetry. It
has six bending cells and six dispersion free straight sections. The main parameters of the ring are summarized inTable 1. Fig.2 shows the envelope functions of two cases,
positive and negative a. Two short straight sections areused for an injection and RF acceleration and the other four
are used for insertion light sources. A type of the bending
cell is a modified DBA with two 34 degrees bends and one-8 degrees invert bend at the middle. The cell has three-124-The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Wavelength (nm)

10-4

102

101

10"210"110°10°Photon Energy (keV)

Figure 1: Expected brilliance of new SUBARU project compared with SPring-8.

7mr,!"\/ \1!Ill! ' I!JIIW ' \Iiiill ' I!JilW ' 'B

ill ' I!JiiW' U~

Figure 2: Twiss parameters of a half of the ring for a-0.001 (above) and a= +0.001 (below). Solid lines, broken lines and dotted lines represent Real line: f3x, broken: /3yand the dispersion(?]), respectively.

dipoles but its neck-tie diagram is basically that of DBA.
The linear momentum compaction factor (at) is controlled
by changing dispersion function in the invert bend keeping the achromatism. The designed emittance of the ring isroughly 707rnm, which is close to the theoretically attainable limit for that bending structure [2].
The natural energy spread is 0.072% at E = 1.5 GeVwith a = 0.0012 where the natural bunch length is Ut =27ps. Our first goal of the bunch shortening is Ut = 3ps,or lmm, which would be obtained at a--- 10- 5 . Here the intrinsic bunch shortening limit came from the quantum fluctuation of the path length is O.lps [3].
The ring has three sextupole families in dispersive sections in order to control two chromaticities and the .second
order momentum compaction factor (a2). This would be an
essential part of the quasi-isovhronus opeartion. One family is pole-pace windings set inside the gap of each invert
bend in order to minimize the coupling between the families. This enables to keep the enough dynamic aperture withadditional two families at dispersion free sections [4].
One HOM damped cavity with SiC duct developed andused at INS-SOR and KEK-PF[5] is installed. The SiC
absorber eliminates the resonant impedances up to n =800. The DC power supply for the klystron is a newly designed crowbarless power supply using IGBT inverter unit[6], which voltage ripple is very small in low frequency region. This characteristics is very important because the synchrotron oscillation is so slow in a quasi-isochronus operation that it could be resonant with the ripple.
Main part of the vacuum chamber is made of aluminum.
Its cross section at the straight section is a flat hexagon with-125-

The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

insertions
S-U
L-U

SC-W
OK (undulator)

Table 2: Main parameters of insertion light sources of New SUBARU.
Number of perid gap (mm)Kphoton wave length (nm)763025"'58
1.3"'5.38.1"' 149
5420025"'44.50;8"'2.51.4"'29
30262
0.1"'0.23
3501401.7"' 12200"' 12000
160/32032.5/16.5

Au (mm)5 REFERENCES

Table 3: Beam lines to be constructedPurpose
Source Energy(keV)
EUVLBM
0.08"'0.3
LIGABM3
Coherenct exposure L-U
0.08"'0.3
Material processing BM< 1Material analysis
BM<1FELR&D
OK0.006
X-ray microscopeS-U0.3"'0.6
Topography
SC-W>2[1] T. Mochizuki et al., "First Lasing of LEENA Free Electron
Laser at LASTI", Proc. 18th Int. FEL Conf., Rome, August
1996.
[2] Y. Shoji etal., "Emittance Optimization of New SUBARU",
Proc. of 16th RCNP Osaka Int. Symp. on Multi-GeV HighPerformance Accelerators and Related Technology, Osaka,
March 1997.
[3] Y. Shoji et al., Phys. Rev. E 54 (1996) R4556.

inner height of 28mm. The structures in the vacuum chamber, such as vacuum slots or tapers, are designed according to a simple guide line; the longitudinal impedance Zo,Lshould satisfy IZo,L/nl < H1 for n < 10 3 and IZo,L/nl <10- 1 n for n > 103 . The pumping system is designed tokeep an averaged vacuum of 4 x 10- 7 Pa when 500mA isaccumulated in the ring. It guarantees a Touchek life time
longer than 10 hours.

[4] Y. Shoji etal., "Sextupole Correction Families of New SUBARU", Proc. of 16th RCNP Osaka Int. Symp. on Multi-GeV
High-Performance Accelerators and Related Technology, Osaka, March 1997.
[5] M. Izawa etal., Rev. Sci. Instru. 66 (1995) 1910 & 1926.
[6] H. Kozu etal., "A Crowbarless Power Supply for Klystrons",
Proc. of SRI'97, Himeji, August 1997.
[7] T. Watanabe et at., "Design of Beam Line Optics for EUVL",
Proc. of SR1'97, Himeji, August 1997.

3 INSERTION LIGHT SOURCES
Table 2 summarizes the parameters of four insertions, theyare the long undulator (L-U), the short undulator (S-U), thesuperconducting wiggler (SC-W) and the optical klystronfor the FEL (OK). L-Uis 10.8 m long, however it consistsof separable 8 units in order that its length is changable byreplacing units. SC-W is a three pole wiggler of which maximum field strength is 8 T. The undulators of OK are plannertype using electric magnets. One can choose their period
160mm or 320mm. The period is changed by re-connecting
the coils. The storage ring will be operated at 0.5 ""' 0. 7 GeV.
for FEL. The energy spread widening by the microwave instability was estimated using Keil~Shnell criteria. However
the FEL would have gains more than a few thens % withpeak current of 1OA and the impedance of IZL IJn = 0 .10.
A distance between mirrors is one fourth of the ring circumference.

4 BEAMLINES
The ring has rooms for 4 beam lines from insertions and9 beam lines from bending magnets (BM). Table 3 lists 8beam lines scheduled to be constructed. Two beam lines
will be constructed every year. In this first year, Japanesefiscal year 1997, the lines for EUVL and LIGA are underconstruction [7].

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