PRESENT STATUS OF JSR, K.Yanagida,H.Yokomizo,T.Harada,M.Yokoyama,T.Nagai,K,Mashiko,Y.Ishizaki, and H.Tayama,
Synchrotron Radiation Research Team,Japan Atomic Energy Research InstituteTokai-mura,Ibaraki-ken.319-ll,Japan
Table 1JSR.

ABSTRACTJSR .has been in operation since April
1989. Some quantities were measured at
135MeV that was an injection beam energy. A
beam current is accumulated up to 5.6mA. A
beam lifetime is observed to be -30min at
300MeV, which is mainly determined by acollision with residual gas and slightly
depends on the beam current. Tunes andnatural chromaticities were measured as
Vx=2.23, vy=0.84 and ~x=-1.82, ~y=-1.28. The
tunes agree with ones calculated by SYNCH
code.
INTRODUCTION

Principle parameters of Linac and~Energy
Repetition rate
Peak current
Pulse widthlJlsec.J.S.B.
Stored energy
Injection energy
Circumference
Bending radius
TunexyJSR is an electron acceleration/
storage ring which is located in the linac
building as shown in Fig.l. Principle
parameters of the linac and JSR are given inTable 1. JSR takes the Chasman-Green latticewith a superperiodicity of three. There arelong straight sections of -l.Sm even in thesmall ring(see Fig.2). Each cell iscomposed of two bending, a single quadrupole
and two pairs of doublet quadrupole magnets.
A dispersion function is variable bychanging the single quadrupole magnet. It is
possible not only to suppress the dispersion
but also to leave it on the long straightsection. The tunes can be selected bychanging the field strength of doublet
quadrupole magnets. The linac beam energy isavailable from several lOMeV to 150MeV. The
injection energy is chosen at 135MeV because
the linac is able to supply a high intensity
beam at this energy. After the electrons areaccumulated sufficiently in the ring thebeam energy is increased up to 300MeV.
The linac was used for several
experiments beside JSR. The machine-time for
JSR is dedicated only one or two weeks amonth. The experiment is performed indaytime.

Energy loss
RF frequency
Peak RF voltage

lSOMeV
1Hz-lmA

135MeV
O.SHz-SOmA

300MeVlSOMeV or less20.546m
0.835m
2.23
0.83
0.86keV/turn at 300MeV
116. 7MHz30kV

The description of design, construction
and performance of components, for example
magnets or rf cavity, are given in theprevious papers 1)2)3)4).
EXPERIMENTAL SET UP
The actual operating point of thebetatron tune is chosen around vx=2.23 andvy=O. 83.
Thebetatronfunctionsanddispersion function is shown in Fig.3.
The beam current stored in JSR ismeasured by DCCT(D.C. Current Transformer).
The tunes are measured by RF-KO(RadioFrequency Knock Out electrode) and the CCD
camera which observes the synchrotron

Fig.2 Plane view of JSR

Fig.l Plane view of linac building-4-10.---------------- ----------.
86E42.1 ~--~~--~-----L----~----~----L---~600
4002000246TIME (sec.)

LENGTH (m)Fig.4 Time evolution of beam current at 135MeV
Fig.3 Betatron and dispersion functions
radiation light. RF-KO gives a periodicorhorizontally
eitherperturbation
vertically to the beam. The resonance will
occurs if the frequency of RF-KO fKo follows
fKo= (m±v) f rev where m is some integer. Hereis taken m=-2 for vx and m=l for Yy. frev isthe revolution frequency. The magnitude ofresonance is observed as an increase oftransverse beam width on the TV monitor.
The chromaticity is measured by theconventional method like that the rf
frequency frf is changed to measure the tune
shifts Av. The relation is Av=-~dfrtlfrfll· a
is a momentum compaction factor calculated
as a=0.12 by SYNCH.
The acceleration of the stored electronis slowly carried out with a time period of
5 min, because all magnet are made of ironblock type. The characteristics of the eddycurrent are different in the bending magnets
theAftermagnets.
quadrupoleandcharacteristics are well studied, it is able
to reduce the time for ramping.

ABc'01 ow_.......r__s..Jo_o_ __,__1_o..J.o_o_ _.__1_5..Lo-o-~--2-'ooo
TIME{sec.)

Fig,S Time evolution of beam current
Beam energy is increased up to 300MeV.

EXPERIMENT
Fig.4 shows a time evolution of thebeam current just after stopping injection.
Here the beam energy is 135MeV. The decayrate of the beam current is slightly
depending on the beam current. Below 2mA thelifetime becomes constant and it is 8min.
This value is deduced to be explained by thecollision with residual gas. At a better
vacuum condition, the lifetime becomes
longer around lOmin. Fig.S also shows thetime evolution of the beam current at threedifferent mode; storage at 135MeV denoted A,acceleration denoted B and storage at 300MeV
denoted C. The lifetime at 300MeV isobserved to be -20min. In ;o, better vacuum
condition the lifetime is obt.ained to be-30 min.
In order to evaluate the lifetime ofbeam current two effects are considered. OneThe Touschek
is the Touschek effect.
lifetime tT is calculated at 135MeV by ZAP.
They are tT=900sec without the effect of theintra-beam scattering and tT=l.lxlO 4 sec
with this effect. It is reported5) that theeffect of the intra-beam scattering appears
especially in the low energy and low naturalemittance ring. The Touschek lifetime issupposed to be longer than 900sec. Other isthe photodesorption effect. A vacuum chamber
is not sufficiently aged by synchrotron
radiations. The photodesorption effect may
affect the beam lifetime especially at
300MeV. To study these phenomena, furtherexperiment and analysis are necessary. It isespecially important to measure the beam
momentum spread,bunch length,
size,

-5 -

betatron function, and vacuum pressure atdifferent conditions.
The synchro-betatron resonance isobserved horizontally and vertically. Fig.6
shows the normalized beam width when theresonance tune is changed. The tune with themaximum width is regarded as the betatrontune. The interval between the resonances
are measured to be -1.0x1o-3 and thesynchrotron tune is calculated as 0.996x1o3. The satellite resonance appears away thebetatron tune by mv 5 , where m is an integer.
If there is the instability due to the ion
trapping or other effects, the tunes ofsatellite resonanceshift
toward thebetatron tune. It is thought any instability
is not observed in this experiment with thecurrent of -0.3mA.
2.5 ,----...------,----.--~--,

til

f<

t:l

H

a:2.0~

Pol1%1..

Fig. 7 shows the tune shift tJ.v whenmomentum is changed by scanning the rf
frequency. Then the chromaticities aremeasured~x=-1. 82
and ~y=-1. 2 8.
Thechromaticities calculated by SYNCH are ~x=1. 42 and ~y=-2. 20. It is reported that thevalue of chromaticity does not agree with
one calculated by SYNCH in the case of asmall ring?>. It is needed to calculate byanther code or method. While the tunes at
dp/p=O are vx=2. 23 and vy=O. 84.
Theyreasonably agree with expected value
calculated by SYNCH; vx=2.26 and vy=0.86.
This means all the magnetic components work
correctly as they are designed.
CONCLUSION
Through the experiments with low
current JSR and its components are proved towork correctly. Here is described theexperiments at the typical operating point;
vx=2.23, vy=0.83 and the dispersion remains
onthelong straightsection.
Other
operating point was surveyed for example
with double achromatic.
The lifetime of the beam current isobserved to be -10min and -30min at theenergy of 135MeV, 300MeV respectively. The
lifetime seems to be mainly determined by
the vacuum condition, and slightly depends
on the beam current above 2mA.

t:l

Pol

ACKNOWLEDGEMENT

H

..:1~

1.5

The author wish to thank K.Nakayama forthe computation. I also wish to express mythanks to the collaborators.

0:z:

REFERENCES
1.0 L--~-LI..L....J....L..-..JL..L-..LJ'--.....I..J.....__~_.....J;l.;234
2.236
2.238
2.240
2.242
TUNE

X

Fig.6 Synchro-betatron resonance00.010•dv xt.v y

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S)J.Leduff,Nucl.Instr.and Meth.,A239,83(1985)
6)J.Janger,D.Mohl,PS/DL/LEAR/Note,81-7(1981)

00.006

•>

<I0•

0II

0.002

0II•
.0.002-0.006-0.004-0.002-0.0000.002

dp/p
Fig.7 Measurement of chromaticity-6-