JAERI-Conf 95-021

3p1-4
The Tohoku University Stretcher-Booster Ring
Masayuki OYAMADA, Bibo FENG, Jirohta KASAGI, Osamu KONNO, Akira KURIHARA,Masakatsu MUTOH, Toshiharu NAKAZATO, Masashi NANAO, Tadahiro OONUMA,Yoshinobu SHIBASAKI, Masumi SUGAWARA, Shigenobu TAKAHASHI, Tadaaki TAMAE,Shigekazu URASAWA, TatsuyaYAMAKAWA, lMasahiro KATO, 2Takashi MOMOSE
and 3Goro ISOYAMA
Laboratory of Nuclear Science, Tohoku University
1-2-1 Mikamine,Taihaku-ku, Sendai 982, Japan
1KEK, National Laboratory for High Energy Physics
1-1 Oho, Tsukuba 305, Japan
2Miyagi National College of Technology
48 Aza-Nodayama, Shiode, Medeshima, Natori 981-12, Japan
3Institute of Scientific and Industrial Research, Osaka University
8-1 Mihogaoka, Ibaraki 567, JapanFor the booster and internal target modes, the injected
Abstract
electrons are accelerated using an RF cavity up to 1.2 GeV
The Tohoku University Stretcher-Booster Ring Project
within 0.4 second. Since the storage ring is dedicated towas approved this year. This ring plays three roles: the pulse
synchrotron radiation and electrons are injected at thebeam stretcher, the booster and the storage ring for the internal
target nuclear experiment. It has four 3.1 m long straight maximum energy, we can expect the high stability of theelectron orbital motion. Except the period of injection to thesections and its circumference is 50 m. The maximum energy
storage ring, the STB may be used for the nuclear experiments
is 300 MeV as the stretcher and 1.2 GeV as the booster.
simultaneously. The vacuum system of the storage ring will be
isolated using a thin foil or differential pumping system, weI. INTRODUCTION
can use gases for the internal targets in the STB.
In the 1970's, the intermediate energy electromagnetic
Figure 1 shows the layout of the STB. The circumference
nuclear physics had made the compelling needs for new highof the STB is 49.75 m and it has four 3.1 m long straightintensity continuous electron beam accelerators. Several
laboratories in the world had actively studied design sections which are used for the injection, the extraction, theinternal target experiment and the RF acceleration. Parametersalternatives with the objective of constructing acceleratorsofthe STB are listed in Table 1.
which can meet the needs of future research program. Some ofThe beam is extracted fast by using kicker magnets forwhich have been realized as the MAMI, Mainz microtron, thethe booster mode and is done slowly using the third integer
pulse stretcher rings with existing linacs at Saskatchewan,
Bates and NIKHEF, and the entirely new superconducting
linac at CEBAF. We have proposed the pulse stretcher ringprojects since 1978.[1]-[7] A prototype 150 MeV stretcher
ring (SSTR) [8] was constructed in 1981 and has been used forcoincidence experiments for 14 years. The Tohoku UniversityStretcher-Booster Ring was approved this year and will becompleted in 1997.

II. GENERAL DESCRIPTION
The stretcher~booster ring (STB) plays three roles: thepulse stretcher ring mode which accepts pulsed beam from the300 MeV Linac and delivers external continuous beam for thenuclear coincidence experiments, the booster ring mode which
accelerates electrons up to 1.2 GeV and injects them intoanother storage ring by fast extraction, and the storage ringmode which holds the beam at 1.2 GeV for internal target
nuclear experiments.
Pulsed electron beam from electron linacs is not suitable
for the coincidence experiments, and then we need a pulse
stretcher which stretches pulsed beam to continuous one. Theenergy of electrons extracted from a stretcher is the same as
the injected energy, 300 MeV in this ring-463-

Figure 1. The layout of the STB.

JAERI-Conf 95-'021

resonance (vx = 3.33) for the stretCher mode. The later casethat the electron energy should be kept constant by RFacceleration is so-called "achromatic extraction." The STB has
two RF acceleration systems, a 2856 MHz system is for thestretcher mode and a·500 MHz system for the booster and theinternal target modes. No RF system is needed for stretcher
mode operation under 250 MeV and electrons are extracted bymeans of "monochromatic extraction".
Table 1. Parameters of the STB.
Machine Parameters
Circumference
LatticeSuper Period
Betatron Tune
Momentum Compaction
Factor
Chromaticity
RF Frequency
Beam Parameters
Stretcher mode
EnergyEnergy Loss per Rev.
Energy Width
Damping Time

Emittance
Booster Mode
EnergyEnergy Loss per Rev.
Energy Width
Damping Time

Emittance

49.7512m
DBA

4
Vx=3.300
Vy= 1.200
a=0.037767~X= -5.7861~y= -4.9791

500.1/2856.24 MHz

300MeVUo = 2.39x10 4 MeV
AE/E = 1.209x10-4
tx = 7.921xlo-1 sec
ty = 7.13lxlo-1 sec
ts = 3.396x1o- 1 sec
Ex = 8.585x1o-9 m·rad

Table 2. A quarter lattice of the STB
Configuration
Ot- QF-02-QD-~-BM- ~ -QC-~-BM-~-QD-02-QF -01
Drift Space
1.5625 m
Ot
02
0.50m
Bending Magnet
Bending Angle
45°
Bending Radius
3m
Length
2.355mooEdge Angle
Quadrupole Magnet QM
Length
QF=QD=0.3m
QC=0.4m
Bore Radius
R=0.05mQF k = 2.0617 m-2
Focus (horizontal)
QC k = 2.737 m-2
Defocus (horizontal)
QD k = -2.2287 m-2
Modulated Quadrupole Magnet PQM
Length0.1 m
Bore Radius
0.05 mk=0.2m-2
Modulated Sextupole Magnet PSX
Length0.1 m0.06 mBore Radius
k =10m-3
i0 . ll

i1s

DFi!IDi

ccc:::J 0 c:::J cc

1.2GeVUo = 6.11x1o-2 MeV
AE/E = 5.8xto-4
tx = 7.23x1o-4 sec
ty = 6.51x1o-4 sec
ts = 3.10x104 sec
Ex= 1.717xi0-7 m·radlll. STRUCTURE OF THE STB

I.

The STB lattice has a DBA (Double Bend Achromat)
structure and consists of eight bending magnets, twenty
quadrupole magnets, a modulated quadrupole and a modulated
sextupole. Laminated iron plates are used for all STB magnets.
The bending radius of the magnets is 3 m in order to install theSTB in the existing experimental room which is 16m wide,
and to realize a long straight section for the internal target
system. The magnetic field of bending magnets is 1.33 T at
1.2 GeV. Electrons are injected inside of the ring and theinjection beam line from the linac crosses STB orbit. The
outside extraction line meets the pulse beam line from thelinac. Table 2 shows parameters of a quarter lattice of theSTB. Also Figure 2 shows betatron and dispersion functionsof a half part of the STB.

FD3!'IllDi

c0 c:=J 0 c::::::J cc
1.~

0I

I

1.0.~

0.~

rcu

3

ccc::::::J 0 c:::J cc(:§:·~

FDcaf

f:

I(LL

0.0

Path Length (m)Figure 2. Betatron and dispersion functions of the STB.

-464-

JAERI-Conf 95-021

IV. RF SYSTEM

Table 3. Parameters of the RF system.

Two types of RF system are installed in the STB. One is
500 :MHz system for the booster ring and internal target modes
and the other is 2856 MHz system for the stretcher ring mode.
Parameters of RF system are listed in Table 3.
For the booster ring and internal target modes, the 500
MHz system is chosen since a high power RF source isrequired for acceleration up to 1.2 GeV. Devices around 500:MHz are commonly used at many accelerator facilities and areavailable at reasonable price. The cavity is a single cell withtwo nose cones which has been optimized at KEK and its
shunt impedance is 5 MQ. A 100 kW klystron is adopted toaccelerate and to compensate the synchrotron radiation energy
loss in the bending magnets as well as the energy loss forhigher order mode excitation.
The 2856 :MHz system is installed for the stretcher mode toaccept all the electrons from the linac without spill. In thismode, the stored current jumps up from zero to 300 rnA within
0.5 ~sec. and falls down linearly to zero until the next
injection. This scheme is repeated at 300 cycles per second.
Because it is difficult to control RF voltage and phaseaccording with such rapid change, we adopt a cavity with very
low shunt impedance and with input coupler of very large
coupling constant (~=15). Then the voltage and phase ofaccelerating field are kept within small fluctuation.

V. CONCLUSION
All components of the STB, except RF system and magnet
power supplies for booster operation, will be installed next
spring, and we will start commissioning for stretcher mode
operation.
The Tohoku 1.5 GeV low emittance storage ring proposal
is under investigation, and it shall hopefully follow completionof the STB. The STB will provide electrons to the storagering.

Maximum Energy
Maximum Current
RF Frequency
Harmonic Number
Shunt ImpedanceOver-voltage Factor
Acceleration Voltage
Quantum Lifetime
Synchronous Phase
Synchrotron Freq.
Klystron Output
Wall Loss
Number of Cavities

Booster Mode
1.2GeV
300mA
500.1 :MHz83
5MQ
6.0367kV
38 hours
80.4°
59.5 kHz
lOOkW
27kW
1Stretcher Mode
300MeV
300mA
2856.24 :MHz474
0.25M.Q
122.87 kV
85.2°
197kHzsoow

32.9W
1VI. REFERENCES[1) Y. Torizuka, Proc. 2nd Symp. on Ace. Sci. and Tech.,Tokyo, 277 {1978).
[2] T. Tamae, Proc. 3rd Symp. on Ace. Sci. and Tech., Osaka,343 {1980).
[3] M. Sugawara, Proc. 4th Symp. on Ace. Sci. and Tech.,
Saitama, 287 (1982).
[4] M. Sugawara, Proc. 5th Symp. on Ace. Sci. and Tech.,
Tsuk:uba, 406 (1984).
[5] M. Sugawara, Proc. 6th Symp. on Ace. Sci. and Tech.,Tokyo, 307 (1987).
[6] M. Oyamada, Proc. 8th Symp. on Ace. Sci. and Tech.,
Saitama, 453 (1991).
[7] M. Oyamada, Proc. 9th Symp. on Ace. Sci. and Tech.,
Tsuk:uba, 486 (1993).
[8] T. Tamae et al., Nucl. Instr. & Meth. A264, 173 (1988).

-465-