JAERI-Conf 95-021

PA21
Construction of 100 MeV Electron Linac in Kyoto University
Toshiyuki Shirai, Takeshi Sugimura, Masaki Kando, Masanori Ikegami,
Yoshihisa !washita, Hiromi Okamoto, Sigeru Kakigi, Hideki Dewa,Hiromu Tonguu, Hirokazu Fujita, Akira Noda, and Makoto Inoue
Nuclear Science Research Facility, Institute for Chemical Research,
Kyoto University, Gokasho, Uji-city, Kyoto 611, Japan
Katsuo Mashiko
Nihon Kensetsu Kogyo Co Ltd., 5-13-11 Shinbashi, Minato-ku, Tokyo 105, Japan

Abstract
Table 1 Beam parameters of the linear accelerator.
An electron linear accelerator and a compact storage ring
have been constructed at Kyoto University. The beam energy ofthe storage ring is ·300 MeV and will be utilized as a synchrotron
radiation source. The output beam energy of the linac is 100 MeV
and the designed beam current is 100 rnA at the pulse width of 1j.lsec. The construction of the linac had been finished and the test isunder going. The electron beam of 300 rnA is extracted from theelectron gun and the peak RF power of 20 MW is successfully fed
to the accelerating structures at the pulse width of 2 j.lsec.

100MeVEnergy
Beam Current
Pulse Width
Maximum Repetition

lOOmA
1j.lsec
20Hz

1. INTRODUCTION
A compact electron storage ring (Kaken Storage Ring, KSR)
and the linear accelerator are now under construction at the Institutefor Chemical Research, Kyoto University [1); The layout of theaccelerators is shown in Fig. 1. The KSR has a race track shapeand the maximum beam energy is 300 MeV. It will be used as thesynchrotron radiation source from the dipole magnet and theinsertion device. The critical wave length of the synchrotron
radiation is 17 nm. It will be also used for the research of the freeelectron laser.
The beam energy of the electron linear accelerator is 100
MeV. Table 1 shows the main beam parameters. For the linac
constriction, some components of the JAERI linac were transported
from the Japan Atomic Energy Research Institute (JAERI) to theKyoto University [2]. The linac is used for the beam injection tothe KSR and some beam experiments. The beam parameters are
determined by the condition of the beam injection to the KSR andthe restriction of the size of the building, Photo 1 s-hows the view

Photo 1 View of the front part of the accelerator. The electrongun, the buncher, and the first accelerating structure fromthe right to left.

Electron Strage Ring

Optical Beam Course

Undulator
or Wiggler
5mElectron Injector

Quadrupole
Magnet No.I

Quadrupole
Magnet No.2

Quadrupole
Magnet No.3

Quadrupole
Magnet No.4

Figure 1. Layout of the electron linac and the KSR.

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Mag11etNo.S

BeamDump

JAERI-Conf 95-021

of the front part of the accelerator.
Table 2 Main specification of the injector.

2. ACCELERATOR
The electron gun has the Pierce electrode and the cathodeassembly is the Y-796 (Eimac). The maximum extraction voltage
is -100 kV. The pulse width of the grid pulseris variable from 10
nsec to 1 jlSec. The beam current of 300 rnA has been achieved at
the pulse width of 1 jlSec.
The pre-buncher is a single reentrant cavity. It is designed
to bunch the beam within the phase spread of 60 degree. Thebuncher is a disc-loaded and 3 step constant gradient structure. It
has 21 cells and the total length is 777 mm. The designed phasespread is within 3 degree at the beam current of 100 rnA when
the input power is 12 MW.
There are three main accelerating structures. The main
characteristics of the accelerating structure are listed in table 2.
The maximum electric field is 45 MV per an accelerating structure
without beam loading at the input power of 20 MW.
The doublet of the quadrupole magnets is used as a focusing
element between the accelerating structures. The calculated beam
radius along the beam axis is shown in Fig. 2. It is assumed thatthe normalized emittance is 100 1t·mm·mrad. The calculated beam
radius is kept within 6.5 mm along the beam axis. The steeringcoils are placed at the entrance of the first and the third accelerating
structures.

Electron Gun (Pierce type)
Cathode Assembly
Extraction Voltage
Accelerating Structure
Mode
Number of Cell
Bore Radius
LengthOperating Frequency
Maximum Electric Field
Klystron (ITT-8568)
Cathode Voltage
Output RF PowerGain

2/37t, Const. Gradient85
11.74- 13.4 mm
3m2857MHz
15 MV/m at 20 MW
250kV, 250A
21MW
53 dB·):'- AIIJj-'J

Hl=? ~~mv p.;H"=" ~~mv
ll~mV;~~·~'mv p.;H4=::.
Ot; P*Ioc f' *IDC P~I•rvr

3.RFSYSTEM
The block diagram of the RF system is shown in Fig. 3.
The master RF oscillator is a synthesized signal generator (HP8664A). The booster klystron (TH-2436, Thomson) has a gain of40 dB and the output power is 10 kW. The pulse width is 3.5
jlsec. The output power is divided by the 4-way RF divider andsupplied to the four main klystrons. RF attenuators and phaseshifters are inserted between them.
The main klystron is ITT-8568. The maximum output poweris 21 MW. Figure 4 shows the input RF power of the buncher
and the three accelerating structures. The peak RF power is 12
MW at the buncher and 20 MW at the accelerating structure. TheRF frequency is 2857 MHz and the repetition is 7 Hz. The RFpulses are picked up by the directional couplers and detected by
the RF diodes.
The modulator is composed of the high voltage power
supply, the pulse forming network (PFN) and the pulse
transformer. The stabilized power supply for the modulator isY-796 (Eimac)-lOOkVDC\ tf·'1~,.

--)/I/'"'t---- v

.....

..

I~~f;

[r'- ...A.

,,~.)\ ........ 1 l.l~.

"\I',J...

f__lj

Ii

Figure 4 Input RF pulse to the buncher and the three
accelerating structures. The peak power is 12 MW
and 20 MW, respectively. The repetition is 7Hz.

~~
0Buncherc::m--A,...c-c...-1----.
Q-mag.l

15000

(mm)

20000

~~~==~~~====~0
BeamQ-mag. 5Dump

Figure 2 Calculated beam radius along the beam axis. The normalized emittance is assumed to be 100 7t·mm·mrad.

-83-•f.j

I100:J I· f.f

JAERI-Conf95-021

Wave GuideControl RoomAccelerator RoomDirectional Coupler(·60dB)

Figure 3 Block diagram of the RF system

adopted to keep the electron beam energy constant. The maximum
voltage is 25 kV a'ld the current is 500 rnA. The voltage stability
is less than 10·3.1t feeds the electric power to the three PFNs forthe accelerators at the repetition of 20 Hz.
4. BEAM MONITOR
The current monitor is installed between the acceleratingstructures. The monitor is the ferrite core with the coil. The current
sensitivity is 1 mV/rnA.
The beam profile monitors will be installed at the close tothe current monitors. The material of the beam screen is analumina ceramic in which a little chromium oxide ishomogeneously doped (Desmarquest, AF995R). The beam profile
monitor is also used for the emittance measurements combinedwith the upstream quadrupole magnets

connected by the optical fiber each other. The fiber cable isolates
each devices and reduces the noise. The master controller is apersonal computer IBM-PC/AT with ISA GP-IB card (AT-GPIB,National Instrument). The control software works on the Microsoft
Windows system. A user can operate by the mouse or a touchpanel.
6. SUMMARYThe construction of the 100 MeV electron linac had been
finished and the tests of the main components such as the klystrons
and the electron gun were carried out. We succeeded to feed the20 MW into the accelerating structure at the repetition of 7 Hz.
The conditioning work is now in progress. The beam acceleration
test of 100 MeV is scheduled in autunm 1995.
7. ACKNOWLEDGMENTS

5. CONTROL SYSTEM
The block diagram of the device control system is shownin Fig. 5. The controller units have the GP-IB interface andThe authors have grateful thanks to the Dr. Kobayashi andDr. Shoji at JAERI for their advises about the electron lina9. We
also thank to Mr. Shoda and the staffs of the Nihon Kensetsu
Kogyo Co Ltd. for their work. Mr. Kazama at ICR helped us forthe construction and we would like to present our thanks to him.

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REFERENCES

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Optical!fiber-----r---Control
Room[1] A.Noda, et al., "Electron Storage Ring, KSR for Light
Source with Synchrotron Radiation" , Proc. of the Particle
Accelerator Conferecnce, Dallas, USA, 1995, May,in press[2] H.Takekoshi, et al., "Design, Construction andOperation of JAERI-Linac", JAERI-Report 1238, 1975

AcceleratorRoomFigure 5 Block diagram of the control system.

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