The 9th Symposium on Accelerator &ience and Technology, Tsukuba, Japan 1993

Present Status of SOR-RING
Hirofumi KUDO, Kenji SIDNOE, Hiroyuki TAKAKI, Tadashi KOSEK!, Haruo OHKUMA and Yukihide KAMIYA
Synchrotron Radiation Laboratory, The Institute for Solid State Physics, The University of Tokyo~

has also been improved by changing the operating point of the ring (seeSec. IT). Recently, we measured the fundamental parameters of the ringsuch as betatron and dispersion functions, chromaticity and RF-cavity
parameters. Moreover, it was proved that SOR-RING is capable ofincreasing its energy up to 450 MeV or more. Some results of machinestudies are presented in Sec. m.

SOR-RING [1] is the oldest ring that has been constructed as a ring
dedicated to synchrotron radiation experiments from the start. Itsconstruction was completed in 1974. The ring is, however, being
improved and its accelerator studies are still active. In the 1992 summer
shutdown, beam position monitors (BPM's) [2][3][4] were installed in thering and the BPM system that used PIN diode switches showed a goodperformance; the relative accuracy was 0.3 to 0.4 J.lm Recently the beam
lifetime became by a factor of two longer; it was obtained by changing thebetatron tunes and by applying a few kV on the ion-clearing electrodes.
In this paper, we will present an operational status of the ring and some ofrecent machine studies [5].

Table I. Principal pammeters of SOR-RING+
Injection energy
Storage energy
Circumference
Bending radius
Bending field
RF frequency
Harmonic number
Revolution frequency
Horizontal tune
Vertical tune
Momentum compaction
Natural emittance
Horizontal damping time
Vertical damping time
Longitudinal damping time
Critical photon energy
Energy loss per tum
Energy spread
Bunch length
Synchrotron frequency
RF Voltage

308 MeV
380 MeV17.4 m
1.1 m
1.15 T
120.83 MHz (at present)
7
17.3 MHz
1.23 (typical)
1.19 (typical)
0.636-320 nm·rad
31 msec
26 msec
12 msec
110 eV
1.7 keY
3.0 x 10-4-10 em
110 kHz (typical)
22 kV (typical)

I. Introduction
SOR-RING is located in the site of the Institute for Nuclear Study(INS), the University of Tokyo, but the facility of the ring belongs to theSynchrotron Radiation Laboratory (SRL), the Institute for Solid State
Physics (ISSP) of the same university. Electrons with an energy of 308
MeV are injected into SOR-RING at a repetition rate of 1 Hz from ES,
Electron Synchrotron of the INS, which is a 21-Hz rapid-cycle machinewith a maximum energy of 1.3 GeV and provides the electrons to theirown users. Electrons injected into the ring are accelerated up to 380 MeV
and then stored until the next injection. Figure 1 shows the plan view ofSOR-RING. The ring is 17.4 min circumference and consists of eight
bending magnets and four quadrupole triplets. The ring parameters arelisted in Table I.
In last summer shutdown, four vacuum chambers for quadrupole triplets
were replaced by new ones in order to install BPM's. A purpose of theBPM's is to test a BPM system that has been developed for the future planof a VUV and soft X-ray high-brilliant light source [4], and the otherpurpose is to measure the C.O.D. of SOR-RING and correct it by beamsteerings that have been also installed at the same time as the BPM's. The+The parameters dependent on the beam energy are the values at 380 MeV.
beam steerings consist of auxiliary coils wound on every pole of all
quadrupole magnets, so that a quadrupole can produce both horizontal andII. Operational Status
vertical dipole fields by exciting appropriate pairs of four coils or change
The ring is usually operated from morning to night, sometimes theits quadrupole strength to measure betatron function. The conductor ofnext morning, with the beam injection three times per day, and the weekly
coils is 1.8 mm in diameter and the number of turn 196 per coil. At
schedule is from Tuesday to Friday in accordance with the schedule of ES.
present, auxiliary coils of two quadrupoles in a triplet are used for
The operation time in a fiscal year is continually increasing as shown insteerings and those of the remaining one for changing its quadruple field.
Fig. 2. Total operation time in. the 1992 fiscal year was about 2100 hours
In the summer shutdown we also replaced manually-controlled shunt
including injection and machine study. The initial current of stored beam
resistances for changing bending fields with computer-controlled electric
was around 200 mA and the beam lifetime about 200 minutes at 200 rnA.
loads. With these systems, we measured the closed orbit distortion
Figure 3 (a) shows a typical example of 1992 daily-operation of the ring.
(C.O.D.) at the first time since the ring had been constructed, and further
corrected both horizontal and vertical C.O.D.'s much less than 1 mm by Until then, the operating point was near a sum resonance (see Fig. 4) andit seemed that the growth of beam size due to the resonance helped toexciting the steerings and changing the RF frequency.
decrease the Touschek effect at a high current. However, the beamsometimes fluctuated in size, probably due to a combined effect of the sum
resonance and the ion trapping.
2500

r--------- -.

'iii'iS 2oooe 1500
Q,O

E=
1':1~1000

Q,O500EQ,

00 'i:s4'ts~sHs~6.-!87!-8~8H8~9~9~o!'!91H9e'2

Fiscal Year
Fig 1

Hi 2

Schematic of SOR-RING

When new vacuum chambers for triplets were installed, ion-clearing
electrodes were also incorporated in them.' At present, a few kV Devoltage is applied on the ion-clearing electrodes in the routine operationof the ring. With the DC voltage ·applied, the beam lifetime has been
improved by a factor of two at a high current. The lifetime at a low current

Operation time versus fiscal year

Therefore, we changed the operating point to a new one, near thedifference resonance of Vx - vy =0, as shown in Fig. 4. As a result, thebeam lifetime was increased by a factor of two at a low current. In
addition, about 2-kV DC voltage was applied to ion-clearing electrodes.
Then the lifetime was improved even at a high current as shown in Fig. 3-44-(b). Figure 5 shows an example of the lifetime when the operating pointis the new one but no DC voltage is applied on the electrodes.
250 ~~~~--~--~--~1~l

800200t""'

600i'§'=g

8400!..
9azoo.§:=

percent of the average density of electron beam. Here it was assumed thatthe electrodes with a few kV completely cleared otherwise trapped ionsoutside the beam orbit; in Fig. 3 (b) the lifetime does not apparently
depend on the beam current, while in Fig. 5 it increases inversely
proportional to the beam current. For the Touschek lifetime, thecalculated value is much less than the measured one as seen in Fig. 7,
where we assume that zero coupling horizontal emittance be the naturalone, x-y coupling the full coupling, and the bunch length 16 em, which is
the measured one at 200 mA [6]. The discrepancy between calculation andmeasurement has not been settled yet; probably the actual beam size would
be larger than the calculated one.

12250
TIME

<.s 200

250 ~~--~~~--o-~1000

jzooc 150

800 t""'r;;
600 ~-!'50

01::

u" 100"400~u 100§"""Ill200~= 50

500
CE:Ciearing Electrode500090468
Operating time (hour)

2TIMEFii 3

Daily o.peration of SOR-RING (a) jn 1992 and (b) {rom 1993 ApriluTune diagram

Estimated life!jme (Touschek ± ~:as-scatterin~:lIII. Recent Machine Study
It was found with the BPM system that maximum values of uncorrected
C.O.D.'s are horizontally about 3 mm and vertically 4 mm at 380 MeV, as
shown in Fig. 8 (a). It was also found that the present RF frequency does
not conform to the ring circumference since the average of horizontal
C.O.D. along the ring is about 2 mm. At the injection energy. themaximum horizontal C.O.D. is about 9 mm. In SOR-RING, however, it
seems that the large orbit distortion at the septum helps the injection. Tocorrect both horizontal and vertical C.O.D.'s, we excited the beamsteerings. In addition, we changed RF frequency by about 100 kHz tocorrect the horizontal C.O.D. As a result, both horizontal and vertical
C.O.D.'s were corrected within 0.3 mm as shown in Fig. 8 (b). The user
run with the corrected C.O.D. is, however; postponed until the next
autumn, since the SR beamlines have to be realigned to meet the neworbit.

TIME

Lifetime without DC vo!ta~:e awlied on the electrodes

54

54Fjg 60

There are accelerator problems in SOR-RING yet to be solved; (1)relatively high vacuum pressure around the RF-cavity probably due tooutgassing from the elastic vacuum seals of the cavity, and pressure
growth with the beam current, which might be caused by heating of two
glass windows near the cavity due to synchrotron light (see Fig. 6), (2) alongitudinal instability caused by a higher-order-mode of the RF-cavity;
for multi-bunch mode the threshold currents of longitudinal instability areabout 3 mA at 380 MeV and 1 mA at 308 MeV, and (3) the biggest
problem is that every ring component is aging rapidly. The first problem
will be fixed in this summer shutdown by replacing the elastic seals withHELICOFLEX seals and also by replacing an existing light port with anew one; two glass windows of the port being used for profile and current
monitors are directly irradiated by synchrotron light and at present thetemperatures on the windows become more than 100 °C. The second will
be cured, for example, by inserting damping antennas in the RF-cavity.
Finally, the best solution for the third one is to construct a new ring, ahigh-brilliant light source.

v.
Fig. 4Fii 7

103322I 01

TIMEvacuum pressure in the rio~:

80 -1

We have estimated the lifetime due to residual gas (coulomb scatteringand bremsstrahlung) using the measured vacuum pressure around the ring(see Fig. 6). The estimated result is shown in Fig. 7. We have also
estimated the lifetime due to trapped ions; this lifetime may be inversely
proportional to the beam current, if the density ratio of trapped ions tostored electrons is kept constant. The calculation using measured
lifetimes indicated that the density of trapped ions would be about 5-45-u -2-3-4-5

QlFig.!j(a)Q2

Q3Q4Ql10-1-2-3-4-5--o-- Xc.o.n.
- ...o.- • Jc.o.n.

Ql. .

(b)
Q2II

Q3Q4!l!)I!!!~;Qrr~ted C.O.D. !In!! !hl correct~ C.O.D.

Ql

Continuous measurement of the beam orbit revealed that (I) the orbit
slowly varies by the order of several tens of J.tm during a storage mode, (2)before and after injection it also jumps by several tens of J.tm, and (3)horizontal orbit sometimes fluctuates in a period of a few ten minutes or
have variations like square waves. A typical orbit drift is shown in Fig. 9.
We measured betatron function f3 at quadrupole magnets by exciting
auxiliary coils wound around the magnet poles, and dispersion function TJ
at BPM's. The measured fractional variation, !lf3/f3, was within 20
percent, and the distortion of TJ within 0.2 m (see Ref. 5 for these figures).
We also measured chromaticity. The measurement showed that thechromaticities in both directions are positive and large in spite of a smallring, whereas their theoretical values are horizontally -2 and vertically
0.2 (also see Ref. 5 for these figures). This discrepancy has not been
settled yet.

I~~"§0.8 -----.::-.)--,...-------...... 0.2j,0.0'------·;;~'.au.=====-~~
Vertical

0.6 HI
0.4 ,__0.2-c2li;:r:- -0.2.

Horizontal~ - ~ ,._,. ...,...,

11'i""~'.-;1,ll"""...............

-0.2";-\I.

Ii'I

12

16

18

20

22

14

Q

g:

-0.6

0.0
10- -0.4

l'lAM.

-0.8
24

where Vbr = loRs /(! + {3), V}r = 4{3 · Pg · J?. /(1 + {3) 2 , ~=synchrotron phaseand t=-2QL "4/!f. f being the resonance frequency of cavity. In a case ofSOR-RING where the RF cavity is largely detuned and Va is relativelysmall, the t.f is approximated by (the exact expression for the optimumtuning),
M- -fRF J?.sintjl M~- 2QL Vc(1+{3) .
We can therefore observe an effect of beam loading by measuring Llf in afunction of beam current. Figure 10 shows the measured result, which wellagrees with the theoretical prediction.
In a recent machine study, one of the BPM's was connected to a hybrid
circuit that can produce RF signals directly proportional to the beam
positions. The RF signals were then fed into the BPM system and in turninto a FFT analyzer in order to find how the beam positions werefluctuating in a low frequency region.. Figure 11 shows the Fourieranalyzed signals of vertical beam position. In the figure, (a) is the casewhere the synchrotron, ES, is operated with a repetition rate of 21.25 Hz.
while (b) is the case where ES is turned off. Clearly, some of lowfrequency fluctuations have their sources in ES. On the other hand, thefrequency spectra around 10 Hz seen in both figures are probably generated
from SOR-RING itself. Presently, however, we are not sure which sources
cause the fluctuations; magnetic field, AC line noise or mechanicalvibration of ES, and air-conditioner, cooling water system or the othersystems of SOR-RING. WithES operational, the amplitudes of fluctuation
were horizontally 2.6 J.tm and vertically 0.6 J.!ffi at 21 Hz.

TIME

Fi& 9~

Orbit drift

We newly measured RF power and transmission/reflection coefficientsof the RF-cavity. The measured parameters of RF-cavity are listed in Table
IT. The value of Va in the table is a theoretical one and the V c is deduced
from Va and the measured synchrotron frequency. Resonance frequencies
and Q-values of the higher-order-modes (HOM's) were also measured andtheir changes due to the cavity tuners (called flappers) were examined, but
the data of HOM's have not been fully analyzed yet.

"§0'§8'<1.)(/)

i:.Ll

120.83 MHz
5 kW (typical)
0.4 kW (typical)
22 kV (typical)
1.68 kV at 380 MeV
1.1 MQ

Coupling coefficient f3
Tuning range of flappers

1.22500kHz~~~~~ ~ ~~~~~ ~ i~~~·==100:::::::: i::::;:;: ;;;;:;·

10~s:

rnae0.1("t>0.
00.01

0.1

0.001

O.Dl-5·a:Table IT Parameters of RF Ci!vity
RF frequency fRF
Generator power Pg
Cavity power Pc
Cavity voltage Vc
Accelerating voltage Va
Shuntimpedance Rs
Unloaded Q-value Qo
Loaded Q-value Qr..

100102030

40~~50frequency [Hz]Fi~,llFr!.JQll!i:n!:Y :ll2~ra Qf Y!l!li~al beam 12Q~iliQn

It was proved that SOR- RING has a capability of accelerating the beamup to 450 MeV or more with a minor modification; the critical photon
energy then becomes about 200 eV. Indeed, a low-current beam of a few
tens of rnA was successfully accelerated to 450 MeV without any
appreciable beam loss. To accelerate a high-current beam as much as in
the present user run, however, we have to replace the glass windows as
described in Sec. II. After replacing them in this summer shutdown, wewill try the 450-MeV operation for a high current.

6.4xl032.9xl03

0.05

VII. Acknowledgments
We would like to thank Prof. T. Ishii. Director of Synchrotron
Radiation Laboratory of ISSP, and the other staff members for theircontinuous encouragement and full support.

0.00~ -0.05

6... -0.10

[1]

<l

[2]

-0.15

[3]
Fi~. 10

Measured beam loadin~
The solid line is the theoretical calculation.

[4]

Using these data. we measured the beam loading of RF-cavity.
Generally the beam loading may be expressed by;(Vet+ vbr sintjl) 2 + (Vc + vbr costjl) 2 = vg~•

[5][6]-46-VIII. References
T. Miyahara eta!., SOR-RING An Electron Storage Ring Dedicatedto Spectroscopy, Part. Accel.. Vol. 7, pp. 163-175. 1976.
K. Shinoe et a!., Design and Calibration of Pickup-Electrodes for
Beam Position Monitoring at SOR-RING, submitted to 1993
Particle Accelerator Conference, Washington. D.C.
K. Shinoe et a!., Beam Position Monitoring System using PIN
Diode Switches, submitted to 1993 Particle Accelerator Conference,Washington, D.C.
Accelerator Group, A Future Plan of VUV and Soft X-ray HighBril/iont Light Source, in these proceedings.
H. Kudo eta!., Measurement of the Orbit Parameters at SOR-RING,
submitted to 1993 Particle Accelerator Conference, Washington,D.C.
T. Koseki eta!., Measuremem of Beam Bunch Length in SOR-RING,
in these proceedings.