CHARACTERISTICS OF THE SUPERCONDUCTING VERTICAL WIGGLERAND OPERATION STATUS IN THE PHOTON FACTORY
H. Kitamura, M. Kihara, S. Sato, T. Shioya,
E. Takasaki, I. Mikuni and T. Yamakawa
National Laboratory for High Energy Physics
Oho-machi, Tsukuba-gun, Ibaraki-ken, 305, Japan
I. Nagakura
Faculty of Education, Gunma University
Maebashi, Gunma-ken, 371, Japan

M. Niwano
Miyagi University of Education
Sendai, 980, JapanThe closed orbit during excitation is corrected byapplying appropriate correction currents on two outercoils, so as to keep the position of electron orbit
unchanged, which is observed by the beam profile
monitor 4 •Figure 2 shows the correction current as a function of the main current. The correction current is acomplex function of the main current especially at low
fields because of the each iron pole and magnetic
shield is in different magnetized state in the processof excitation.
In order to make the residual orbit distortion
small enough not to disturb the experiments using
photons, the correction currents have to be controlledwith an accuracy of 0.01 ampere. Actually, the exciting currents are controlled by a pattern generator
using a micro-computer, so as to ascertain the reproducibility of the excitation.
The reproducibility of the beam position have been
confirmed by' observations at several experimental
stations and turned out to be satisfactory.

INTRODUCTION
The superconducting vertical wigglerl 2 3 of thePhoton Factory has been installed in the storage ring
The first operation with 2. 5 GeV
in October 1982.
electron beam was successfully achieved in February
1983. The wiggler radiation was observed by a fluorescent plate via a Be window in the beam line. The
spectra of the wiggler radiation were measured with asolid state detector, by changing the field strength of
the wiggler, under the condition of small current.
From November the operation of ·the wiggler started
again. The main purpose of the operation in November
and December was tuning-up of the wiggler itself, suchas to decide the wiggler excitation pattern which does
not introduce closed orbit distortion, and to find thebest operating tunes with respect to the beam lifetime.
At the same time, experimental beam lines weretuned up using the wiggler radiation. Since February
1984, the wiggler has been operated in the user's timein parallel with other beam lines.
ORBIT CORRECTION
The vertical wiggler magnet of Photon Factory is a
3-pole superconducting magnet. The schematic drawing
There are a central coil ofis shown in Fig. 1.
nominal field strength of 6 Tesla and two outer coilsof 3 .Tesla. Three coils are connected in series andexcited by a main power supply. Also, two auxiliary
power supplies are connected to the outer coils.

10<I:cQ)
.....
.....

5:::1(.)

c0+=(.)
Q)
.....
.....

tank0100
Main Current (A)

0(.)

-5
chamberFig. 2magnetic
shieldcasing
shaped beam
duct

Correction current as a function of themain magnet current.

TUNE SHIFT OF THE BETATRON OSCILLATIONAs the wiggler consists of three short dipole
magnet with parallel pole edge and generates magnetic
field in the horizontal direction, the betatron tune
should be shifted only in the horizontal plane by anamount of /:;v given approximately byawet;v = !TpFig. 1= 2.1 x 10-3 2Bw

where a is the betatron function at the location for
the wig~ler, e is the half bend angle in the centralpole with radius p, and B is the excitation of thew
wiggler in Tesla.

Cross-se.ctional view of the superconducting
vertical wiggler.
189

On the other hand, in the first commissioning of thewiggler with 2.5 GeV electron beams, no correction wasTheneeded to excite the wiggler up to 4. 5 Tesla.
initial tunes at the first stage of the wiggler
operation were measured as v = 5. 265 and \! = 4.174,
respectively. Afterwards, iChas become cle~r throughthe tune diagram survey that the tune shift curve, suchas in Fig. 3, does not overlap the dangerous resonanceregion if the starting operation point is chosen appropriately. But, correction is need for the present
initial tunes, v = 5.390 and v = 4.153 because they
are chosen so as ~o avoid beam irlstabilities as well as
to improve injection efficiency.

Figure 3 shows the variation of the betatron tune
as a function of wiggler field. As seen in Fig. 3, thehorizontal tune shift agrees well with calculated
value. However, the betatron tune varies also vertically due to the non-linearity in the magnetic field of
the wiggler. Details on this problem will be discussed
As increasing theelsewhere in this Proceedingss.
wiggler excitation, dangerous resonances appear near of
Therefore, precise control of
the operating point.
betatron tunes is essential to obtain the long enoughlifetime. The tune shifts are corrected automatically,so as to keep the operating point unchanged in the tune
diagram. This is done by changing currents of the ring
quadrupole QF and QD' by the aid of a control computer.

OPERATION STATUS
By means of the tune correction, the beam lifetime
became longer as in Fig. 4.
The wiggler magnet has operated at 4.5 Tesla
usuaLly, because the long lifetime enough for theuser 1 s run has not been achieved at the fields morethan 5 Tesla.
The beam lifetime is also limited by vacuum
The vacuum pressure in the down stream ofpressure.
the wiggler increase by one order of magnitude due toheating up of the vacuum chamber by wiggler radiation.
The pressure dependence of the lifetime can beseen clearly also in Fig. 4. Liquid helium are supplied with a container by the central cryogenic
facility of the low temperature group located two
kilometer apart from the storage ring.
Helium are transferred every four hours to thewiggler cryostat through a 12 meters long transfer linefrom the container which was placed in the service areaof the storage ring building.
Consumption of liquid helium is 4 liters per hour,
and transfer loss is about 50% of it.

Tune shift due to wiggler

5.3

4.3

5.2

4.2

----- ---o-'0--o- -o..

Vertical ( vy)"Vx-o...-o..--a.

..... .....

vy'

4.1

5.1

02

54

3B (Tesla )Fig. 3

Variation of the betatron frequency at 2.5~} measured,
GeV with wiggler excitation,-----predicted from parallel pole edgemodel.

LIFE TIME (-)(min.)
1200

Pave. ( • )

1000

0.8

800

0.6

I0- 9 torr
I600
0.4
400
0.2

200
20Fig. 440 60 80 100 120 140 160 180
RING CURRENT (rnA)
Beam current dependence of the beam lifetimeand the average vacuum pressure.
190

REFERENCES
1.

2.
3.
4.

5.

K. Huke, T. Yamakawa: Nucl. Inst. and Meth. 177(1980) 253-25 7.
C. Lesmond KEK Reports KEK80-17 March (1981).
T. Yamakawa, H. Kitamura, S. Sato, E. Takasaki, T.
Shioya and C. Lesmond: Proc. of the 4th Symp. onAccel. Science and Tech. Nov. (1982) 315-316.
S. Shibata et al.: Contributed to this symposium,
Synchrotron sidebands in betatron oscillation
measured by means of RF knock out in the PF
storage ring.
M. Kihara et al.: Contributed to this symposium,
Stability of the betatron oscillation during theoperation of the superconducting wiggler in thePhoton Factory.

191