DEVELOPMENT OF A SUPERCONDUCTING COMPACT STORAGE RING "NIJI- ill" FOR INDUSTRIAL APPLICATION
Katsuji Emura , Yasumitsu Tsutsui , Fujio Miura , Hiroshi Takada
Osaka Research Laboratories, Sumitomo Electric Industries,Ltd.
Shimaya,Konohana,Osaka 554,Japan
Takio Tomimasu
Electrotechnical Laboratory
Umezono,Tsukuba,Ibaraki 305,JapanABSTRACT

GENERAL DESCRIPTION OF NIJI- ill

We have developed a superconducting compact
storage ring "NIJI-ill" for industrial application. The
configuration of NIJI- ill is a four-cornerd type whosesize is typically 3m x 5m. Since this ring is designed
for x-ray 1 i thography, a peak wave 1ength of thesynchrotron radiation spectrum is set about 5 Aandthis ring is capable of wide exposure by the electron
undulating method. We succeeded in the first beamstorage with one superconducting bending magnet andthree conventional magnets on September 27,1989 and astored current is estimated at 20 rnA at present. The
general design and the present status of this ring will
be reported in a later section of this paper.

Since x-ray lithography needs a severe resolutionof less than 0. 25 p. m, several specifications are needed
as follows.
(1) A peak SR spectrum is set in the range of 510 A, because of the resolution determined by Fresnel
diffraction and the secondary electrons.
(2) A stored beam current of more than 200 rnA isneeded, because of the photon energy density on thesurface of semiconductor wafers taking account of thesensitivity of resist material and the absorption
property of Be window.
(3) A stored beam size of less than 1mm at the SR
source points is needed in order to reduce a penumbrablurring.
The main parameters which satisfy thosespecifications are shown in Tab.l and calculated SR
spectrum is shown in Fig.l. The schematic configurationof NIJI-m is shown in Fig. 2. NIJI-m is a fourcornered type whose size is typically 3m x 5m. Thisring consists of four superconducting bending magnets,
two vertical-focusing quadrupole magnets(Q2,6) and six
horizontal-focusing type(Q1,3,4,5,7,8). The structureof lattice functions and a beam size at the conditions
listed in Tab.l are shown in Fig.3 and Fig.4
respectively. Achromatic conditions are realized in thelong straight section (4.1m long). This brings aseveral advantages as follows.
(1) It is capable of avoiding a deterioration ofinjection efficiency due to an energy dispersion ofinjection beam.
(2) Suppressing syncro-betatron resonance becauseof keeping achromatic conditions in the rf cavity.
(3) By exciting a sextupole magnet at thissection, it is capable of magnifying a dynamic aperture
without a change in chromaticity.
The maximum beam size of both horizontal andvertical direction at the bending section are less than
0.5 mm, which satisfy the above specifications.

INTRODUCTION
Recently synchrotron radiation(SR) has been
regarded as a practical light source for x-ray
lithography and photon-induced chemical vapor
deposition. The compact rings, in order to apply anindustrial use, have been developed around the world
since the early 1980's. The key issues for realizing acompact ring system are a low-energy injection system
and a superconducting bending magnet. The benefit ofusing a low-energy injection system is a lower cost
system, but it has been pointed out that it is not easy
to store a high beam current at this scheme.
Electrotechnical Laboratory (ETL) and Sumitomo ElectricIndustries,Ltd. (SEI) developed a compact ring, NIJI-I, in order to examine a low-energy injection. In thoseexperiments, it was demonstrated that the high beam
current storage above a 500 rnA was achieved at aninjection energy of 100 MeV. On the other hand, acompact ring with superconducting bending magnets has
been developed in recent years due to the advantage ofbeing able to decrease a bending radius with its strong
magnetic field. SEI has been developing asuperconducting compact storage ring, NIJI-m, since1986 in the high energy experimental room of the ETL
linac facilities. Since this ring is designed for x-ray
lithography, a peak wavelength of the SR spectrum is
set about 5 A and this ring is capable of wide SR
exposure by the electron undulating method1J. Before
the superconducting magnets are installed, NIJI-ill withconventional magnets has been already constructed inJune 1989 in order to study a beam optics and theoptimum injection parameters. The conventional magnets
will be replaced with superconducting magnets one byone. One of four conventional magnets has been alreadyreplaced with a superconducting magnet, and wesucceeded in the first beam storage on September
27,1989.
In this paper, the general design and the present
status of this ring is reported.

SUPERCONDUCTING MAGNET2)
The most important issue for realizing a highcurrent storage in the superconducting storage ring isthat the superconducting bending magnet has precise
magnetic field. Since the designs of thesuperconducting magnet for NIJI- ill was carried out at
the above point of view, a cos e winding type and an
air-core type were introduced in it. A cos e winding
type, as well known, has an attractive property ofhaving a good field region widely in comparison withthe any other winding type. The magnetic field
homogeneity of less than 5xlo-4 was obtained within ±30 mm in the radial direction ,which was in good
agreement with the values calculated by 3-D magnetic-344-

analysis. Also the compensation for the sextupole
f1eld at the magnet coil ends is easy by means ofmodifying a coil shape in order to produce the inverse
field of t~e originally produced sextupole field.
Although th1s type has a defect in difficulties oftaking SR light out of inside the superconducting
magnet, two SR ports can be installed in asuperconducting magnet in practice. On the other handan air-core type has the advantage that a magneti~
field distribution scarcely changes during an exciting
phase because of no existence of magnetic material.
This is ~ ve~y important property in the compact
storage r1ng w1th a low-energy injection scheme becauseof the enormous change in an exciting current. Thesu~erconducting magnet consists of two coils, a mainco~l to produce a dipole field and a quadrupole coil toadJust a magnetic field gradient called field index.
~his index can be varied from 0 to 0.5 by an
Independent operation of both coils. Since Nb-Ti
material was used for superconducting wire, the coils
must be.cooled down by immersion into liquid helium.
Its boll-off rate is about 10 1/h at the maximum
exciti~g current of 1774 A. This rate is dominantly
determined by the thermal penetration through a power
lead. Therefore, if a high temperature superconducting
wire is used as a power lead or a permanent current
mode is used, this rate will be able to decrease.
f~eldVACUUM SYSTEM3)
Since both Touschek and quantum lifetime at thebeam energy of 615 MeV can be sufficiently lengthened
due to high rf voltage, the lifetime of a stored beam
is dominantly limited by the scattering effect caused
by a residual gas at the early stage of beam
experiments.
The vacuum system in NIJI- m is designed to keep
an ultra-high vacuum of less than 1x1o-9 Torr in thebeam duct even at the stored beam current of more than200 mA. In order to realize the above condition, thetotal pumping speed of 9000 1/s is needed taking
account of that the photon stimulated gas desorption
coefficient is kept small owing to the sufficiently
exhausted SR absorber. Eight sputter ion pumps andeight Ti getter pumps are installed in the four
straight sections and the estimated total pumping speed
reaches 8500 1/s. At the bending section, since thebeam ducts which are cooled down at 4.2 K act as thecryogenic pump, the estimated total pumping speed willreach about 28000 1/s. This value is large enough incomparison with above specification because the photon
stimulated gas desorption coefficient is expected toolarge at the early stage of beam storage experiments.

Tab.1 Main parameters of NIJI- ill
Stored Energy [MeV]615
Bending Magnetic Field [T]4.10
Bending Radius [m]0.5
Circumference [m]15.54
Synchrotron Radiation Loss [keV/turn] 25.3
Periodicity
2
Harmonic Number
8Radio Frequency [MHz]154.317
rf Voltage [kV]100Stored Beam Current [mA]200
Critical Wavelength [A]12
Betatron Tune (vertical)
1. 25(horizontal)2.25
Momentum Compaction Factor
0.077
Energy Spread
7. 28x1o-4
Emittance (vertical) [mmmrad]
0.025(horizontal)[mmmrad]
0.25
Injection Rate (maximum) [pps]10

Fig.2 Schematic configuration of NIJI-m
B1-4
Ql-8
Sl-3
K

1.0,-----,..----,---~-~<bending magnet
quadrupole magnet
sextupole,octupole magnet
kicker magnet

10-'

!:

:,

e 10-'

E.;;:~

s. 1Q-3z.

·u;c:£"a: 1 o-•(/)

1 a-• '-----'----'--___j__.L.J
0.1
1.010
100 1 000
Wavelength (A)Fig.3 Structure of lattice functions

Fig.l Calculated spectrum of SR from NIJI-m-345-estimated at 20 mA at present. The measured horizontal
and vertical betatron tune were 2.2 and 1.1
respectively, they were scarcely changed by that
replacement. The horizontal and vertical beam size were0.07 and 0.13 mm respectively, both values were alittle large in comparison with the designed values .
This phenomenon can be explained by the effect for thelongitudinal coupled bunch instability, because thesynchrotron side band is observed. It is suspected thatsuch a beam size growth will be negligibly small at theconditions of 615 MeV and 200 rnA according to atheoretical analysis.

2.0~-------------------,

Cfx

E'.s"'
N·;;;

E"'"'

CJ

Fig.4 Calculated beam sizes

RF SYSTEM
The rf cavity is a re-entrant type and rf
frequency is 154.3 MHz. Temperature of rf cavity iscontrolled within 40±1 degree in order to stabilize aresonant frequency • The rf power source with a tetrodeis capable of 30 kW maximum. It is even enough to store
high beam current 200 rnA at 615 MeV. The measured
values of shunt impedance and Q-value were 2. 4 MQ and
14000 respectively, those values are large enough torealize a compact rf system.

Fig.5 SR from a superconducting bending magnet

DIAGNOSTIC SYSTEM
Many diagnostics apparatus are installed in NIJIm in order to be easy in the replacement tosuperconducting magnets. Four destructive screen
monitors to search for a suitable injection point areinstalled. Since the position of a screen monitor
located near a septum magnet is externally controlled,
it is very useful to certify a beam position of oneturned beam. The best suited beam positions of an
injection beam were studied in detail in NIJI-ill withfour conventional bending magnets. Therefore a suitableinjection point is easily obtained by this data when
the superconducting magnets are installed.
Also eight beam position monitors for closed
orbit distortion (COD) correction are installed. It isa button shape and its output signal is detected by asuperheterodyne system.
The stored current measurement was carried out
using Silicon photo diode (SPD) which was irradiated bySR. The DC-CT which is often used in compact rings was
not used due to a leakage magnetic field from thesuperconducting magnet.

ACKNOWLEDGMENTS
This project is entrusted by the Research
Development Corporation of JAPAN.
REFERENCES
1) T.Tomimasu, Jpn.J.Appl.Phys. 26, 741 (1987)
2) T.Okazaki et al.,Proceedings of the 11th
International Conference on Magnet Technology(MT-11), August, (1989)
3) F.Miura et al., in Proceedings of the present 7th
Symposium on Accelerator Science andTechnology, Osaka, December, (1989)

INJECTION EXPERIMENTS OF NIJI-III
At first, injection experiments were done withfour conventional magnets in order to search for asui table injection point, tune surveying, COD
measurement and to adjust all components except forsuperconducting magnets. A stored current of 10 rnA wasachieved on July 1989 at injection beam energy of 185
MeV.
The replacement to superconducting magnets wasstarted from early in September and we succeeded in thefirst beam storage on September 27 with one
superconducting magnet and three conventional magnets.
Fig.5 shows a SR light at a viewing port ofsuperconducting bending magnet. A stored current is-346-