THE ACCELERATOR SYSTEM FOR HiSOR
T. Kasuga, T. Ohta, M. Taniguchi, M. Tobiyama
Department of Materials Science, Hiroshima University, Hiroshima 730
I. EndoDepartment of Physics, Hiroshima University, Hiroshima 730
S. HoshiResearch Institute for Nuclear Medicine and Biology, Hiroshima University, Hiroshima 730

Abstract

Basic features

Vve have studied detailed features of the main componentsof the 1.5 Ge V storage ring and the injector machine forHiSOR. Here we briefly report on some selected items; vacuumsystem, single bunch operation and superconducting wigglers.
The conceptual design of the buildings is also described.

The storage ring for HiSOR is designed to have small circumference, 100 m, to be manageable by small number ofoperating crew. The lattice structure is a six-fold symmetric
Chasman-Green DFA type to be operated at 1.5 GeV. The
beam emittance is comfortably small, 7x 10- 8 7!' m rad, which
is a compromise of a high brilliance and a stable operation.
Since the electron energy is relatively low, the SR from thebending magnet does not contain hard x-rays. This feature
is most appreciated by the scientists working with VUV andsoft x-rays. Hard x-rays, whose intensities are comparable tothe one available at KEK-PF, are produced by the high-field
wigglers placed in the dispersion-free straight sections. Mainparameters for the storage ring is summarized in Table 1.
The injector is a combination of a 45 MeV linac and a
1.5 GeV synchrotron. Multiturn injection to the storage ringat 1.5 GeV is envisaged. Since the synchrotron and the linac
are free except at the injection time , twice a day, some plans
are going on to utilize them for nuclear physics and otherapplications. Table 2 shows parameters of the synchrotron.

Introduction
Conceptual design of the accelerator system for HiSOR, a
synchrotron radiation facility proposed by Hiroshima University, has been published in several articles.l11 Since then, we
have been studying practical problems which might affect thecost and performance of the accelerator system. In this paper
we first review the basic features of the HiSOR accelerator
system and then describe some specific parts on which recent
works have been concentrated.

Table 2. Parameters of the boooster synchrotron.

Table 1. Parameters of the storage ring.

Electron energy
Circumference
Mean radius
Revolution time
Superperiodicity
Synchrotron radiation
Energy loss per turnCritical energy for normal
bending section
Long straight section
Betatron tunes

E21rR
RTUo

127.2 kVtc

1.809 keV
6 x 4.875m
5.25
2.25
26.48 kHz
300 rnA
0.0117-10.86-6.90
8.24 ms
7.93 ms
3.98 ms
0.00071
7.20 x 10- 8 1r m radVx
Vy

Synchrotron frequency
Beam current:Momentum compaction factor
Natural Chromaticities

J,Damping times

Tx

Ia:~X~yTy

Energy spread
Emittance (zero coupling)

1.5 GeV
100.71 m
16.03 m335.9 ns
6r,O'e/Etx-341-Maximun Energy
Injection Energy
Repetition rate
Maximum circulating current
Lattice
TypeSymmetry
CircumferenceRF
Harmonic numberFrequency
Peak voltage
Operation mode
Betatron tune
Vx
Vy

Average (3 function
f3x
f3v
Dispersion~'Iaximum 1)x

minimum 1)xEmittance at maximum energy "x

1.5 GeV
45 MeV
0.5 Hz
50 rnAD0 1 FD0 2 F
683.925 m

35125.025 MHz
150 kV

4.25
2.25
3.64 m2.25 m1.78 m
0.23 m
1.2 X 10- 71r m radFig.1 An arist's view of the HiSOR buildings.

Site and building
The site for HiS OR is supposed to be at the foot of a hill in
the new campus of Hiroshima University in Higashi- Hiroshimacity. According to the survey there is a stable granite layer
under the shallow soil. We found that the amplitude of theearth vibration is very small; ideal place for constructing astorage ring. One shortcoming is that the site is not wide
enough for future extension.
An artist's view of the HiSOR building is shown in Fig. 1.
The main entrance for HiSOR is at the leftmost cylindricalbuilding where an auditorium and meeting rooms are situated.
Above the main experimental hall, the central cylinder of SOm
in diameter, there is a corridor connecting the third and fourth
floors of the left cylindrical building to the central tower where
the machine control room is situated. Along the corridor wehave offices for the crew and the visiting scientists. To theright, there is a building for the synchrotron and the linear
accelerator. The upper level of the synchrotron is a utility
room for power sources etc.
The radiation shielding problem for these buildings has
been worked out, the result of which is reported elsewhere.12l

Vacuum system
The shape of the vacuum chamber for the bending section of the storage ring needs a special design because of thefollowing reasons:1) The bending angle in a single magnet is large, 30 degree, so that considerable part of SR will directly hit
the vacuum chamber.
2) We provide two SR ports for each bending section.
3) Single bunch operation is foreseen which requires a low
coupling impedance.

CROTCH ABSORBERION PUMPGETTER
12" LINE50100 emFig.2 The vacuum chamber for the bending section.

An example of the designed vacuum chamber is shown inFig. 2. The RF shield with small holes are provided to reduce
the RF impedance. A large part of the SR is absorbed at thecrotch absorber. The out gas due to photodesorption is meant
to be pumped out from the port at the crotch. According to acomputer simulation, good vacuum, 10- 9 torr CO equivalent,is achieved under the circulation current of 350mA with useof high power distributed ion pumps (DIP), 400 C/s/m, titangetter pumps (TGP) and sputter ion pumps (SIP).
There has also been much progress in the design of thevacuum system around the straight section. \Ve are happy tofind space, though not luxurious, for beam monitors, kickers,steerers etc., as schematically shown in Fig. 3. A simulation
has shown that the closed orbit distortions can be corrected
to 0.1 mm with this arrangement.

-342-DCCT

P1-P30DCCTCTRFKO
F1-F5
V1-V12
H1-H24
K1-K4
GVPosition monitor s
DC current transfor mer
Current transfor mer
RF knock out electrod esFloresce nt plates
Vertical steerers
Horizon tal steerers
Pulsed magnets for injection
Gate valves

CTFig.3 The arrangem ent of various compon ents along the circumfe
the storage ring.

Single bunch opera tion and RF
There is a strong demand for single bunch operatio n at
HiSOR because the existing SR facilities are not quite adequate for the time-res olving measure ment of various type.
In order to enjoy flexibility in number of bunches , a single,
double and triple bunch modes as well as the ordinary 168bunch mode, we are developi ng an electron gun which has acapabili ty of RF modulat ion and fast gating.
It has been known that a part of the electron s escapes fromtheir own RF bucket and is captured by another one due tothe Toushec k effect.[3l This is most serious in the accelera tion
stage of the electron synchrot ron. In order to ensure a goodsingle pulse purity, we have to selectively knock out the electrons in the unwante d RF bucket by applying the fast RF
pulse on the RFKO electrod es. This requires that the neighboring buckets are separate d widely enough for the tail of theRFKO pulse to damp.
Thus we are tempted to use 125 MHz RF frequenc y for thesynchro tron while maintain ing the 500 MHz for the storage
ring. The latter is dictated by the high power requirem ent.
Accordi ng to a standard calculati on, the longitud inal beam
spread at 1.5 GeV for 125 MHz RF is sufficiently small; theportion of electron s to be lost at the injection to the storage
ring is less than 10- 4 •rence ofsmall as 10 /m 2 [tJ. We are designin g a supercon ducting wiggler of which the multipol e field compon ents are extreme ly
small. Another importa nt features impleme nted are a semiautomat ic operatio n and virtually mainten ance-fre e nature.
4A 4.4 T wiggler with required quality seems to be feasible.f lConcl uding remar ks
We have devoted ourselve s on some selected items which,
we deemed, should be studied to some depth before finalizing the detailed design of the HiSOR accelera tor system. The
results are mostly satisfact ory; we are confiden t that the conceptual design propose d earlier, i.e. a small X-ray ring, isfeasible.
In the next step, we are going to study some optionalfeatures to be realized in the second phase of HiSOR project;such as an operatio n mode with a smaller emittanc e, ex. 3 X
l0- 8 1rm rad and very high field, say 6 T, supercon ductingwigglers.

Super condu cting wiggle rs
Possible effect of the strong field wiggler on the beam dynamics in the HiSOR storage ring has been well studied ; thetune-shi ft caused by the quadrup ole compon ent of the wiggler magnet can be compen sated by readjust ing the three Q
magnets , two of them being situated upstream and one downstream the wiggler while the sextupol e field should be kept as-343 -Refere nces
[1 ] M. Tobiyam a et al. Rev. Sci. lnstrum . 60 (1989),
1713;
I. Endo et al., Proc. 6th Sympos ium on Accelera tor
Science and Technology (1987),304.

[2 ] S. Hoshi et al., Contribu tion to this symposi um.
[3 ] T. Kasuga et al. JJAP 28 (1989), 541.
[4 ] K. Aizawa et al. Proc. of 11th Internat ional Con£. on
Magnet Technology, Tokyo (1989).