THE INJECTION LINAC FOR THE 8 GeV SYNCHROTRON RADIATION FACILITY IN JAPANH.Suzuki, H.Yokomizo, H.Yoshikawa, K.Mashiko,M.Iizuka, T.lshida, N.Nakamura, K.Yamada, Y.Suzuki
JAERI-RIKEN Synchrotron Radiation Facility Design TeamJAERI, Tokai-mura,Naka-gun,lbaraki-ken,319-1I.JapanABSTRACT
The injection Iinac for the 8 GeV synchrotron
radiation facility has been designed. It is so designed as
to accelerate both electron and positron beams up to 1 GeV.
The construction of the Iinac wi II be started in 1990. The
research and developments are carried out in several
COIPOnents.
This paper describes the outline and the fundamental
design of the linac.
INTRODUCTION
The new facility for a high brilliant synchrotron
photon source is planned to be established in Nishi-harima,
Hyogo prefecture. The project is carried forward by Japan
Atomic Energy Research Institute (JAERI) and thelnstituteunder theof Physical and Chemical Research (RIKEN),
supervision of Science and Technology Agency (STA).
This facility consists of three accelerators; a 1 GeV
injection Iinac, a 8 GeV booster synchrotron and a 8 GeV
storage ring. First of all, the construction of the linacwill be started in 1990, and the commissioning of thestorage ring is planned in 1995.
The linac consists of three parts; a 100 MeV positronlinac, a 100 MeV electron linac, and a 0.9GeV main linac.
For the future extension of the facility, several beam
extraction area will be considered in the linac.
The current status of the linac design for the 8 GeV
synchrotron radiation facility in Japan is described.
GENERAL DESCRIPTION
The aain parameters of the linac are given inTable 1. These parameters are set by the requirments ofthe acceptance of the synchrotron.
A diagram of the linac is shown in Fig. 1. Theelectron Iinac consists of a 100 MeV accelerating sector.
and a beam transport line. The positron linac consists ofa 250 MeV high-current electron linac, a converter target
to generate the positrons and a 100 MeV accelerating sector.
The main linac accelerates 100 MeV electrons or positrons
up to 1 GeV. The linac is about 200m long. The energy
compression system (ECS) is planned to be placed after themain linac in order to achieve small momentum spread.
There are four beam switchyards ; the confluence of theelectron linac and the positron linac (100 MeV) , twobranches for experimental uses (250 MeV and 500 MeV) andthe end of the 1 GeV linac. The beam diagnostic system of
the linac consists of beam current monitors, screenmonitors, emittance monitors, energy analizer systems and
The 20 m length beam-diagnostics
beam loss monitors.
transfer line is used to measure linac beaa properties.
Fig.2 shows the illustration of the beam pulse
waveforms for the each case of the operation modes.
A long pulse mode and a short pulse mode are designed forboth electrons and positrons. A burst mode which showsin Fig.3 is under consideration to shorten the accumulation
For the future extension, thetiae for the storage ring.
for other purpose, such as thebeams
its
providewill
Iinac
free electron laser in the ultraviolet region and positron
production etc.
Table 1 Linac parametersl. 0 GeV
60 Hz
2856 MHz±0.25 %
1.51!' mm·mrad

EnergyRepetition rate
Frequency
Moaentum spread
Emittance

INJECTOR
The ultimate qualities of the electron (positron) beameaerging from a Iinac depend on the design and operation of
the injection system. We describe the fundamental design ofthe injection system.
The beam characteristics required for the injection
system of the linac is following. The energy is 30 MeV andthe maximum pulse repetition rate is 60Hz. In the case ofelectron linac, one operation mode is 100 mA peak current
for long pulse duration of about 1.3 t.tsec, the other is
300 mA peak current for short pulse duration of about 1nsec. In the case of positron linac, one operation 110de is
10 mA peak current for long pulse duration of about 10 nsec,the other is 10 mA peak current for short pulse duration ofHowever we take aim at more high current
about 1 nsec.
beam in order to shorten the accumulation time for thestrage ring.
Electron linac injector
A diagram of an electron linac injector is shown inFig.4. A beam of 100 keV electrons from a gun is initiallybunched by a subharmonic buncher (which is not used in caseof the long pulse mode) and prebunchers. It is further
bunched and accelerated to 15 MeV in a one meter longstanding-wave buncher. The beam then enters the one meterlong accelerator section in which it is still further
bunched into narrow phase spread and accelerated to 30 MeV.
Solenoidal focusing is used along the entire length of the-355-injector.
The electron gun is of the triode type with 0.5 cm2
dispenser cathode. It will be capable of producing 2.8 A ofpeak current at 100 kV with emittance of 6.5n mm·mrad.
The emission current can be pulsed for the duration of 1.3
p_ sec and 2-3 nsec by varying the grid vo I tage in thetriode.
The subharmonic buncher is a quater-wave re-entrantresonant cavity. The gun pulse beam is bunched within one
half cycle of the 24th subharmonic (119 MHz) of the linac
This allows the beam pulse widthfrequency (2856 MHz).
from the gun to be 2-3 nsec long. The subharmonic buncher
will deliver an electron beam of approximately I nsec pulse
width at 100 kV to following a 2856 MHz prebuncher. In caseof the long pulse mode (1.3 t.tsec), the subharmonic buncher
is not used.
The prebuncher is a re-entrant resonant cavity(2856MHz). The velocity modulation by the prebuncher causes70 %of the electons to be bunched into a 50 degrees phasespread at the entrance of the buncher.
The buncher is a standing-wave structure with aThe accelerator section isvarying a phase velocity.
standard one meter standing-wave structure. The 50 degrees
bunches are caused to enter the accelerator section aroundthe phase stable field null, become bunched to 5 degrees
width, and asymptotically approach the crest of the wave as
they are accelerated.
Positron linac injector
The fundamental constitution of the positron linacTheinjector is similar to the electron linac injector.
isinjector
principal difference between the twoThe gun of the positron linac
specification of the gun.
injector is required high intensity for the sake of a low
conversion (e•;e-) efficiency. The gun is of the triode
type with 2.0 cm 2 dispenser cathode, and will be able todeliver 20 A pulsed beam at 150 kV. The preliminary
calculated emittance is 87 n mm·mrad.

ACCELERATOR SECTION
Energy gain , beam current , beam pulse width ,accelerator frequency and repitition rate are the mostimportant parameters. They lead an accelerator structures,a length of accelerator section and a klystron power.
The linac accelerator sections consist of disk-loaded
waveguides operating in the 2n /3 traveling-wave mode with
There are 25 traveling-wave
constant field gradient.
sections in the main linac. Section length of 3m (effective
length is 2.835m ) for both electrons and positrons is acompromise between the energy gain and the brazing of long
The basic performance criterion is an energy
structures.
gain of 36 MeV per section, with 20-25 MW input power and afield gradient of 13-15 MV/m. Each section consists of 81
elementary cavities except the two end couplers. The
characteristics of the accelerator section are listed in
To achieve a satisfactory field gradient , theTable 2.

vacuum and the surface processing in the accelerator
Bakeout of thesections are under consideration.
accelerator sections is also considered.
The linac operating in the electron long pulse mode
( 100 mA , 1. 3 tJ. sec ) is designed in consideration of theproblem of a beam breakup . One of the design to suppress
beam breakup , is to arrange six kinds of sections. The
effect of this remedy expects to suppress the cumulative
type of beam breakup. Another remedy is to put a quadrupole
triplet every two sections in order to make the wavelengthof the betatron is about 10 m.

Table 2 Ch.aracter ist ic of the accelerator sect ion

Frequency
Accelerator structure
Accelerator mode
RF structure
No. of cavity
Length2856 MHz
traveling-wave
2n /3

constant gradient81
2. 835 II

POSIT RON SOURCE
The linac is required to provide positrons andelectrons with high intensity and high beam quality.
Utilization of positron beam will eliminate the ion
High intensity
trapping phenomenon in the storage ring.
electron beam is requested in order to emerge highintensity positron beam, because of its low conversion
ratio. It is essential to enhance the conversion ratio and
Therefore the positron linac andtransport efficiency.
A small angle
the main linac will be setting straightly.
bending section is set to select positron beam from
It is estimated that positron beam has large
electron.
So the beam transport line
emittance and momentum spread.
must have large acceptance, and ECS should be placed after
the main I inac.
Now we are planning research and developments two
One istypes of positron source at JAERI linac facility.
the conventional type converter which is composed ofa converter target, a pulsed solenoid with strong focusing
field and a positron accelerator section with de solenoid.
Fig.5 shows the experimental apparatus of the conventional
The other is rf focusing type,
type positron source.
in which positrons will be accelerated immediately after
the converter target by the standing wave type accelerator
section with de solenoid.
Positrons emerging from the target have the typicalenergy distribution predicted by bremsstrahlung followed
The energy distribution
by pair-production mechanisms.
Theis inversely proportional to the positron energy.
energy acceptance of the conventional type positron source
is set to utilize the positron energy of 10±5 MeV.
The energy acceptance of the rf focusing type positronsource is set to ntilize lower energy of 2 MeV.
The purpose of the research and developments is tooptimize the position and thickness of the target. We are-356-

also planning to measure the conversion ratio and thecharacteristics of the accelerated positron beam.

REFERENCES

beam

I. T.Harami, H. Yokomizo, et a!., 14th International Conf.

on High Energy Accelerators , Tsukuba, Japan, August22-26, 1989, to be pub! ished.
2. M. I izuka, H. Yokomizo, et al., Proc. 14th Linear
Accelerator Meeting in Japan, Osaka, 181 (1989).
3. T. Ishida, H.Yokomizo, eta!., Proc. 14th Linear
Accelerator Meeting in Japan, Osaka, 181 (1989).
4. P.M. Lapostolle and A.L. Septier, "Linear Accelerator",
North-Holland Pub. Co. (1970), Bl.l.

CONCLUDING REMARKSThe general design of the injection linac and it's
beam parameters was described.
To achieve the reliability, flexibility, and easyis the philosophy of theoperation and maintenancedesigning.
linac
Positron(e-250MeV, e•lOOMeV)/Mainlinac(0.9GeV)~/

Extract ion(250MeV)
Switchyard

D-0-0-i-0-lj
I
Gun

Accelerator sections

Gun

Beao diagnostics I ine

Accelerator sections

Accelerator sections

I
linac

Electron(lOOMeV)

Fig.! Illustration of the linac.
Positrons

Electrons

Long
Pulse

Short
Pulse

~[fllillL ~m++~Ins3nsIOns

1.3ttsIill ~mc- 325 pulse)+IIns-4+Ins~ig.3

Burst mode positron beam

Fig.2 Macropu!se waveforms provided by the linac
pulsed solenoid~'focus coilr-h~ ~~~ ~ ~·(g] ~,--run
IOOkVquadrupole-triplet

subhar1onlc

prebuncher

prebuncher

buncher

No.l

No.2

llSNHz2856NHz

2856MHzbuncher

accelerator

2856MHzsection28561tHz-t"~~~~~HCZJ--+~
analizing magnet

Fig.5 Experimental apparatus of the conventional typepositron source.

Fig.4 Electron source injector.

-357-