The lith Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Recent Progress of the UVSOR Storage Ring
Jun-Ichiro YAMAZAKI, Masahito HOSAKA, Toshio KINOSHITA and Hiroyuki HAMAUVSOR Facility, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444, JapanAbstract

The UVSOR electron storage ring at Institutefor Molecular Science has been operated for nearly 15years as a dedicated synchrotron radiation (SR)source. In the fiscal year 1996, approximately 3000
hours was devoted to provide SR, which includes
single-bunch operation of 4 weeks. Beam stability
and the lifetime have been improved by introducing adouble cavity RF system to suppress longitudinal
coupled-bunch instability. A free electron laser (FEL)experiment for basic research has also been done on
the ring. Because of frequent failures of old devices,many important parts of accelerator system have been
replaced and improved in these years.
1 Introduction

The UVSOR storage ring, a light source for thewavelength region from soft X-rays to far-infrared,
was constructed at Institute for Molecular Science in1983 as a 2-nd generation light source. As importanceof insertion devices is getting higher, the storage ringhas been developed to employ a couple of insertions,and performance of itself has also progressed. Among
four dispersion-free straight sections, one is occupied
Table 1 Parameters of the UVSOR Storage Ring
Lattice type
EnergyCircumference
Superperiodicity
Bending radius
Critical energy
Betatron tune
Momentum compaction aHarmonics
Main cavity RF frequency
Main cavity RF voltage
Energy spread
Natural emittanceBeam size at bend
Bunch Length
Beam current
Lifetime (multi-bunch)* 10 %coupling assumed.

Chasman-Green
750MeV53.2m
42.2m
425eV
3.16 (horizontal)
2.64 (vertical)
0.033
1690.115 MHz (nominal)
50kV
0.3MeV
115 xnmrad0.39 mm (horizontal)*
0.27 mm (vertical)*
170 ps (at zero current)
Multi-bunch 240 rnASingle-bunch 60 rnA
5hat200mA

by the beam injection system. Other straight sections
are arranged for a conventional transverse undulator(2.5 m-long) widely utilized by many user programs,
and for a superconducting wiggler of the wavelength
shifter type with 4 T magnetic field [1], which has
become to be routinely operated. In addition, an
optical klystron employing helical undulators wasrecently installed to provide polarized photons. The
optical klystron is also being used for a basic research
work of the storage ring free electron laser (SRFEL)[2].
By employing a third harmonic cavity [3], which
was commissioned in 1993, the longitudinal coupledunch instability is successfully suppressed byntroducing the Landau damping, then the beamtability has been greatly improved. Moreover theunch length of the electron beam is able to be varied
by changing the RF phase between the main cavityand the harmonic cavity. It is quite powerful tool tocontrol the optimum bunch length particularly in theSRFEL experiment. However, because of relatively
high induced field in the cavity, a complicate
operation for tuning angle and power feed is required.
Further study for operation of the double RF cavity
system is still under way.
Malfunction of devices due to worn-out
accelerator system has been severe problem. Most ofpower supplies for pulse magnets has been replaced
recently. In addition power amplifiers for both main
RF cavities of a booster synchrotron and the storage
ring were switched to all transistor ones. As aconsequence of these renewals of devices, the UVSOR

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-353-The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997accelerator complex is continuously working well.
2 Current Status of the UVSOR Storage Ring
Accelerator complex at the UVSOR facility isconsisted with a 15 MeV injector linac, a 600 MeV
booster synchrotron and a 750 MeV storage ring.
Beam injection into the storage ring is usually done
twice per day at 9 AM and 1 PM. Repetition rate of
the beam acceleration from 1S MeV to 600 MeV on thesynchrotron is - 3 Hz. The electron beam is ramped
up to 750 MeV on the storage ring. Whole procedureof beam injection to store several hundreds rnA beamtakes only 10 min, so that the user's machine time canbe consumed efficiently.
The electron beams at typical initial current of
240 rnA with multi-bunch mode and of 60 rnA withsingle-bunch mode are supplied for user experiments
in regular operation. The lifetime at the initial current
in multi-bunch mode is approximately 5 h byemploying the double RF cavity system. Figure 1
shows variations of the beam current and the lifetime
with the multi-bunch mode a day.
RF power amplifiers for the acceleration cavities
in the storage ring and the synchrotron were also
replaced by new ones completely composed of manytransistor amplifiers. Each identical unit of transistor
amplifier generates power of 700 W maximum. In
case of a couple of units are in failure, the wholesystem can, however, continue to run without any
fatal errors. Consequently the maintenance of thesystem is expected to be easy. Maximum output
powers of the RF amplifiers are 20 kW (30 units) and 8
kW (10 units) for the storage ring and the booster
synchrotron, respectively.
3 Development of Transverse Resonance Kicker

To improve the beam handling on the storagering, a transverse resonance kicker (TRK) system has
been developed lately. On the UVSOR ring, a partial
filling method is used to reduce an effect of the iontrapping in multi-bunch mode. Electron _bunch filling
was controlled by selecting the RF bucket using aFig. 3 Satellite bunch sweeping by using TRK applying toa bucket follows the main electron bunCh.

timing control system for the fast kicker extraction of
the booster synchrotron so far. However it wasdifficult to erase specific bunches so that thetransverse beam instability due to ion-trapping has
been not completely damped and the purity of singlebunch mode has been not very well. The TRK systemgenerates electromagnet ic field with a very shortduration less than 3 ps. To avoid distortion of thepulse due to reflection, whole system including
electrodes and a vacuum chamber was designed to bematched to the intrinsic impedance of 50 n [4]. The
short pulse is synchronized with the revolution of a
specific bunch, which is, moreover, modulated by the
betatron oscillation frequency. Because the electron
momentum on the ring is high (750MeV I c), a huge
power is required to kick out the bunch at once.
Meanwhile, using the TRK system the electron bunchis transversely kicked at each tum, and the amplitude
of betatron oscillation grows rapidly even with arelatively low kick power. The electrons finally may
touch the wall of vacuum chambers or go out of thedynamic aperture. As a result, for example, theimpurity ratio of the single bunch became less thanw- 4- 5 by sweeping the satellite bunches using theTRK (see Fig. 3).
4 UV-FEL Oscillation Using Helical Optical~ysaon·230rAA'1®

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I 0:203 flange
A·A'Fig.2 Side view and cross section of the TRK chamber.

A helical optical klystron employing theSPring-S type undulators was installed in 1996 [5].
The permanent magnet array is consisted with threelanes. The vertical and the horizontal magnetic fields
are provided by the center lane array and the side lane
arrays, respectively. Phase between the center lane
and the side lanes can be changed mechanically, sothat complete helical with both helicities, ellipsoidal
and planar modes of magnetic field are able to beproduced. Because the beam chamber is not fully-354-

The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

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Wavelength (nm)200Gap (mm)Fig. 5 Measured FEL spectr:um ar_ound ~ewavelength
region of 240 nm. Round-trip cavity loss IS also plotted
as a function of the wavelength.

Fig. 4 Measured focusing powers (circles) and calculated
ones (solid lines) against the gap length. Peak magnetic
field of undulator is also shown

surrounded by the magnet arrays like a conventionalhelical undulator, an ante-chamber type vacuum pipe
containing a NEG pump became to be available andthe optical klystron is fully retractable.
Figure 4 shows measured vertical andhorizontal focusing power of the UNK0-3 andpredicted ones deduced from the calculation of themagnetic field. One can see a good agreement
between the calculation and the experiment, andnotices the focusing power is very strong. By using
additional windings of the quadrupoles, the latticefunction can be completely corrected in a gap range
down to 55 mm for the beam energy of 600 MeV. The
distortion of the beta functions increases up to ± 20 %in a smaller gap less than 40 mm because thecorrection current for the quadrupoles is insufficient,however we have not observed a serious bad
influence for the beam at the such small gap [6].
In the lasing experiments, we have used dielectric
Hf02/Si02 multilayers fabricated by an ion-beam
sputtering for the cavity mirrors. Number of layers
has been optimized to obtain the maximum
reflectance, so that the transmittance was rather low.
Although photon absorption rate of Hf increases
rapidly as the wavelength becomes shorter than - 260
nm, we have obtained an FEL oscillation around theshortest wavelength of 240 nm as shown in Fig. 5.
Because the band width of the mirror reflectance isvery narrow, a region which the FEL wavelength wasable to be varied was only from 239 nm to 243 nm .
Acknowledgement
The authors are greatly in debt to Dr. Shiro
Takano of SPring-S who designed the TRK electrodes
with complex consideration of impedance matching.
It is also a pleasure to appreciates the staff member of
the UVSOR facility for their help. These works arepartly supported by the special research program ofInstitute for Molecular Science.
References[1] E. Nakamura, H. Hama, J. Yamazaki, T. Kinoshita,0. Matsudo, H. Yonehara, T. Kasuga, G. Isoyama andM. Watanabe, J. Elec. Spec. 80 (1996) 421.
[2] S. Takano, H. Hama and G. Isoyama, Nucl. Instr.
and Meth. A331 (1993) 20.
[3] K. Tamura, T. Kasuga, M. Tobiyama, H. Hama, G.
Isoyama and T. Kinoshita, Jpn. J. Appl. Phys. 33 (1994)
59.

[4] S. Takano, private communication.
[5] S. Kimura, M. Kamada, H. Hama, X.M. Marechal,T. Tanaka and H. Kitamura, J. Elec. Spec. 80 (1996)
437.
[6] H. Hama, K. Kimura, M. Hosaka, J. Yamazaki andT. Kinoshita, Nucl. Instr. and Meth. A, in press.

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