COMPACT STORAGE RING "NIJI-IV" FOR UV FEL EXPERIMENTT.Tomimasu. S.Sugiyama. H.Ohgaki. T. Yamazaki.
K. Yamada. T. Mikado. M.Chiwaki. and R.Suzuki
Electrotechnical Laboratory.
1-1-4. Umezono. Tsukuba. I baraki. 305 JAPANs. Suse. M. Yoshiwa and A. Iwata
Technical Institute. Kawasaki Heavy Industries. LTD.
1-1. Kawasaki. Akashi. Hyogo. 673 JAPAN
Abstract
Outline of a 500-MeV compact storage ring "NIJI-IV" witha 6. 2 m long optical klystron for the ultra-violet FEL
experiment is describe~ NIJI-IV has a hexagonal configuration with a circumference of 29. 6 m. consisting of
two cells of the triple bend achromat lattice. It will becompleted in 1990 on the basis of the works on compact
storage rings and the visible FEL conducted in thethejointly with
Electrotechnical Laboratory(ETL).
Kawasaki Heavy Industries. Ltd. <KHI ).
Introduction
With the increasing demand for tunable ultra-violet
chemical
photon-inducedforavailable(UV) lasers
processes. free electron laser (FELl is recently receivingmuch attention in japan due to its feasibility of highpower and wide tunability covering a quite wide range ofwavelength from mm to UV. The photon-induced chemical
processes using UV FELs will bring about prospective
industrial applications. since tunable UV FELs can control
photon-induced chemical reactions more precisely thanavailable excimer lasers can d~
After the successful operation of 3. 4 mm FEL using thesuper-conducting linac at Stanford Univ. in 1977 11 • FEL
oscillations have been achieved in the visible range using
ACO ring at Orsay in 1983 2 ' . and in the uv range
using VEPP - m ring at Novosibrisk in 1988 31 .
<~240 mm)
Recently the FEL is considered as sufficiently mature in
the FIR and IR spectral ranges. To my know 1edge. sevenprojects of FELs near the IR and the visible ranges
using linacs are favored for SOl projects and two projectsof the UV range using a 185-MeV NIST microtron and a 1-GeV
storage ring under construction at Duke Univ. in the USA.
The FEL of the UV range needs many technologies such as
accelerater physics of storage ring and linac. FEL
physics. optical technology including optical cavity.
mode propagation and diagnosis. magnet technology fora long optical klystro~ optical elements and so on. TheUV FEL sources available for chemical industries in thenear future. however. should be compact and operated
easily as the compact storage rings proposed and developed for ULSI lithography 41 and angiography 51 •Through the developments of compact storage rings forthese purposes and the visible FELs using a 1. 47 m opticalklystron61 • we have accumulated key technologies needed
for the compact strage ring for the UV FELs reported here.
In this paper. we present outline of a 500-MeV compact
storage ring with a 6. 2 m optical klystron for UV FELexperiment. It will be constructed in 1990 on the basis of
key technologies on compact storage rings and the visible
FEL accumulated in ETL. jointly with KHI.
Technical Backgrounds
Figure 1 shows the 500-MeV ETL Linac and Storage Ring
Facilities. The 500-MeV Linac and buildings have been
constructed in 1980 71 . The linac can accelerate a highenergy - high power electron beam in the energy range of
10~400 MeV.
A 75-MeV beam is used to produce highLow energy laboratory

Slow positron facility(4) Pair spectrometer{3) Betatron control room(2) Measurement and control room
181 Ion pump 191 Buncher ItO! occeleroling
161 Electron gun pulser 171 Electron gun
151 Betatron(12 l Accelerating section(Ill Pulsed deflection coilsection, lens, and ion pump cooling pipe a rrongement(151 Bending magnet (t6l Vacuum duct
{14) Klystron cooling device
cooling device !131 Klystron pulser(17) Quadrupole magnet and ion pump (181 R! irradiation equipment
and cooling pipe arrangement
1201 Compton spectrometer 1211 N 11 1- 1v
1191 Scattering chamber and ion pump1251 Magnet power supply
1241 N I 11-11 I
1221 Ion pump 1231 Beom line I planning I(29) Turbo molecular(28) ECS magnet(27) Beam catcherchannelpionformagnet(261 Quadrupole
1331 SR beam line
1321 RF accelerating cavity
1311 Ti getter pump
1301 Sputter ion pumppump(1) Management roomFig. 1 Layout of the ETL Linac and Storage Ring Facilities-347-

intensity slow posi trans. Electrons of 90~320 MeV are
injected into four compact storage rings; TERAS. NIJI-ll.
NIJI-ill and NIJI-IVCNIJI-means rainbow).
TERAS has been operated on Oct. 19813 '. ETL has also
operated three compact rings. NIJI- I ~m. jointly with
the Sumitomo Electric Industries <SEI ); that is. NIJI- I
has been opera ted on Feb. 1986 9 • 1 0 ' , NI JI-ll on Aug.
198 91 1 ' • 1 2 ' and NI J I- m on June 19 89 H '- NI J I " rr andNIJI-ill have been developed as soft x-ray sources used for0. 25 p. mscale ULSI fine processing.
The visible FEL experiment has been also continued in ETLusing a 1. 47 m optical klystron installed in the 1. 8 m
straight section of TERAS. Total system including an
optical cavity was completed on Aug. 1989. The length ofthe optical cavity is 5. 238 m. Therefore. three bunch
operation at 240 Mev is needed when the visible FEL
experiment is carried out. The cavity loss is less than
1 X lo-• and a gain per pass of 1 x 10- 4 for 2 rnA bunch
The present system
at 570 nm is obtained.
current
including TERAS. however. can yield a gain per pass of
1 X 10- 3 at most at the visible region because of the shortstraight section of TERAS.
Compact Storage Ring NIJI-IVIn the case of compact storage rings with two cellstructure of these lattice. however. the triple bend
achromat type can yield lower emittance beams because theemittance is inversely proportional to the cube of thenumber of dipole magnets. Ditailed study on the choice ofthe magnetic lattice is given in elsewhere''·'.
aFigure 3 shows a schematic layout of NIJI-IV. It is
500-MeV conventional type compact ring with straightsections longer than 7 m where a 6. 2 m optical klystroncan be installed to generate the UV FELs. NIJI-IV has ahexagonal configuration with a circumference of 29.6 m.
consisting of the two cell structure of the triple bend
achromat lattice. The magnetic structure is a combinationof six 60° dipole magnets( p oj, 2m. noQ) with the same
entrance and exit angle of 16.1° and twelve quadrupole
magnets. The lattice order is 0/2 Qf Qd Bd Qf Bd Qf
Bd Qd Qf 0/2 and the periodicity is two. The betatron anddispersion functions for one superperiod of the lattice
are shown in Fig. 4. One of the long dispersion free spaces
is used for the 6. 2 m optical klystro~ The 162. 1 MHz old
RF cavity previously used for TERAS will be used as an
RF cavity. The harmonic number is sixtee~ A stored
current higher than 60 rnA is expected at two bunch
operation. The calculated beame mi ttance is 5 X 10- 8 m. rad.
at 350 MeV.

NIJI-IV should be compact and its straight section wherean optical klystron can be installed is long enough togenerate the UV FEL. The choice of the magnetic lattice isthe beam storage of low
also important to achieve
andhigh current.
emittance. small energy spread.
dispersion free at the optical klystron.
Figure 2 shows ratios of the length of straight section
Ls to the cell length of the magnetic lattice Lc as
a function of Lc on the existing and planned storage rings
worldwide 14 ' . The closed circles show the storage rings oftriple bend achromat lattice. the open circles double
achromat lattice. the closed square FODO lattice. the open
square triblet achromat lattice. and the closed triangle
extended double bend achromat lattice. the solid line of
Ls=6 m indicates storage rings with 6 m straight section.
New storage rings of the third generation such as ALS.
APS. ESRF. SPRING(Kansai), SRRC(Taiwan), Pohang(Korea). TRI
ESTE(Italy) near this line can install many 5 m
undulators to generate high brilliant radiations. The
lattice of these rings is triple achromat type or double
achromat type. The both lattices can achieve dispersion
free drift spaces for insertion devices.

OfOd
OPTICAL KLYSTRON (-6.2m)
NIJI-IV (ETL-KHI)

C = 29.6m

Fig. 3 Schematic layout of NIJI-rv.

NIJI-IV

0.5u~ALSSRS2zMAX§m

ACO:c<"' 0.2!!:VITERAS

UVSOR

...

iSi

HISORo ADONESOR~oNSi~uog • NSLS;
8HE{s~~L• 0• • OCI
SUPERACO'PEP

BEoS5V2::::KANSAI

ID
.....

~__....-- ls = 6m

ALADDINID~~

VIw"'z9coSPEAR

Ls"' 2m--

0,1u

PF

~

BEPC

o,o 5 L_J____.___.__._.L...L_ _ _ _J.___
10__.._~_L....J.__,_L_.L_J_""'---__.J

20

50

100200

Lc: CELL lENGTH ( m)Fig. 2 The ratio Ls/Lc as a function of Lc on the existingand planned storage rings.

-348-0.0

1.93.?

5.6?.19.3
S<ml

11.1

13.0

1'1.8Fig. 4 Betatron and dispersion functions of NIJI-IV.

where N is the number of wiggler magnet periods. Nd thenumber of periods of light of wave length .! passing overan election in the dispersion section. JJ the Bessel
function factor. f the modulation rat& p the peakelectron density in m- 3 • and Ff a filling factor due tothe electron and light beams all along the optical
klystron.
For an electron energy spread of 7X 10- 4 • the value of Nd
attains 100. Therefore. the gain per pass given by Eq. < 2)is roughly proportional to the square of the length of the
optical klystron Lo for the length Lo shorter than 10 m
since Lo = 2N.! 0 + 3.! 0. where 3.! 0 is the length of thedispersion section .
Figure 6 shows a shematic layout of the 6. 2 m opticalklystron. whose main parameters are as follows: the total
length is 6. 2 m. .! 0 is 70 rum and N = 43. A gain per passhigher than 2.3 I is expected for 350 nm at 20 rnA bunch
current from Eq. (2) and a scaling law obtained from thegain measurement of the visible FELs.

0.10,05u0'";;.
...JSR52001

PFBEPC

Ls = 6 m /ESRF
APSKANSAI0005

10Fig. 51000

100Referencesc = 21tR (mlThe ratio Ls/C as a function of C on the existingand planned storage rings.

Figure 5 shows ratios of the length of straight section
Ls to the circumference C as a function of C on theexisting and planned storage rings worldwide.
NI J I-N isthe most compact ring with 7 m long straight section.
6.2 m Optical Klystron
THe FEL wavelength ~ R is related to a wiggler magnet
period ~ o of an optical klystron and to the electronenergy r in units of rest mass m0c 2 by the resonancecondition( 1)

where K 93. 4B(T) ~ o(m) with B being the peak magnetic
field at the wiggler midplane. For instance. B = 0. 315T.
,\ 0 = 0. 07 m. r = 560 (286. 2 J!eV) gives ~ = 348 nm from
Eq. ( 1 ). A gain per pass of the optical klystron for awavelength .! R given by Eq. ( 1) is 1 6 '1)
2)
3)

D. A. G. Deacon at al. : Phys. Rev. Lett. 38. 892(1977 ).
L Billardon et. al.: Phys.Re~ Lett. 51. 1652(1983).
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3523(1981 ).
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No.4. 3133(1983).
9) H. Takada et al. : Proc. Soc. Photo-Opt. Instrm. Eng. 773. 257( 1987 ).
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Sci. and Tech. (INS. Oct. 1987)P. 53.
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12) Y. Oka et al. (This proceedings).
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15) H. Ohgaki(This Proceeding).
16) M. Billardon et al.: IEEE J Quantum Electronic Vol.
QE-21. No.7. 805(1985)

6.2m

A.o= 7Qmm

Xo= 70mm
N43=FIG. 6N= 43

Schematic layout of 6. 2 m optical klystron.

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