DESIGN AND MEASUREMENT OF MAGNETS AND RF CAVITY
FOR THE 1 GEV ELECTRON SYNCHROTRON AT SORTEC
K. Kondo, T. Chugun, M. Kodaira, Y. Yoshiwara and T. Iimura
Keihin Product Operations, Toshiba Corporation,
Suehirocho 2-4, Tsurumi-ku, Yokohama, 203, Japan
S. Nakamura and M. Ohno
SORTEC Corporation, Wadai 16-1, Tsukuba, 300-42, Japan
T. Tomimasu
Electrotechnica l Laboratory,
Umesono 1-1-4, Tsukuba, 305, Japan
Abstract
Design and performance of the magnets and RF cavity
for 1 GeV electron synchrotron which has been installedin SORTEC are presented.
The precise magnetic field measurement apparatus
was developed and applied, then it was shown thatmagnetic field unif~rmity AB/B of the dipole magnets
and magnetic field gradient
was less than 2xl0
uniformity ~!/G of the quadrupole magnets was better
than 2 x 10 •The shape of RF cavity is re-entrant type andaccelerating frequency is 118 MHz. From thecharacteristic measurement in low power level, Rsh of
1.28 Mn and Q value of 15,200 were obtained.
Magnet-Dipole magnet designFig.

The design parameters required for the dipole
magnets of 1 GeV synchrotron are shown in Table 1.
Magnetic field of the magnets is 1.1 Tesla, good fieldregion is +45 mm, bending radius is 3030 mm and magnet·type is re~tangular. The synchrotron consists of 12
dipole magnets.
So as to satisfy the magnetic field uniformity inthe good field region, the shape of cross section wasdetermined by magnetic field analysis used finite
element method. Fig. 1 shows flux line of the dipole
magnet obtained by analysis. For widening effective
field region, the dipole magnets have shims in the bothsides of each pole. Because symmetry of field
distribution is better and deformation of iron core islesser, H-type magnet is adopted.
The synchrotron is operated by 1.25 Hz with risingtime of 400 msecond, so the magnets is made of stacked
laminated 0.5 mm thickness electrical steel. Reducing
the difference of magnetic characteristic among themagnets, electrical steel from the same lot was used
for all magnets.

Flux line of the dipole magnet

Both ends of the magnet were cy) by 4 steps which
The Length ofapproximated the Rogowski's curve.
laminated core was determined based on the result ofmagnetic fringing field obtained by field analysis.
Main coils were cooled with water and consist of 40
turns. Correction coils were installed for correcting
the difference among the magnets at beam injection, but
those were not used.
The assembling accuracy of the magnets was ~0.05 mm
at gap and was ~0.5 mm in iron core length.
Magnetic field measurement of the dipole magnets
The magnetic fiel~)measurement apparatus shown in
It has Hall probe as magneticFig. 2 was developed.
field sensor and moves on 4 axes (x,y,z,a). As theac:uracy of magnetic field measurement depended on
temperature of Hall probe, temperature change was held
within.0.1°C. The Hall probe ~as calibrated by nucl~tr
magnet1c resonance method and 1ts accuracy was 1 x 10

Table 1
Design parameters of the dipole magnets
1540 mm
Core length
55 rnm
Gap height0.044 T
Flux density of gap at injection
1.1 T
at extraction
3030 mm
Bending radius
30°
Bending angle+45 mrn
Good field region
3:5 x 10-4
Field uniformity in the good'field region
12
Number of magnets
Correction coil
Main coil
Coil60 A1300 A--cii'rrent
120Turns/PoleAir
WaterCoolingCore
spicon steel,~terial
0.5 nunRectangularShape
H-type..

Position reproducibility of the Hall probe was less~han 10 11m and magnetic. field was measured by personal
computer automatically.
Fig. 3 shows a result of the magnetic field
uniformity of the magnet. From the measurement resultso~ all m~gnet~, it was confirmed that the mag~~ticin theheld undorml.ty LJB/B was better than 2 x 10
required good field rggion and satisfied thespecification of the synchrotron.
Fig. 4 shows the comparison of analysis andmeasurement about magnetic fringing field at the coreends of the magnet. From this figure, it is clear thatthe analysis value about effective magnetic fringing
field length is good agreement with the measurement
value.
The deviation of the effective length among 12magnets was 1 x 10- 3 • -The dipole magnets for thesynchrotron was arranged with the results of magnetic
field measurement so that closed orbit distortion was
as small as possible.

-149-Table 2
Design parameters of the quadrupole magnet
250 mmCore lengthFig. 2

Field measurement of the dipole magnet
by Hall Probe

Bore diameter

110 mmField gradient
Good field region
Field gradient uniformity
in the good field region
Number of magnets
CoilCurrent
Turns/PoleCoolingCore

5.5 T/m+50 mm _ 3~terial:;_2X

1Q

18585 A
12Water
Silicon steel
to.s mm

6GL/G0 L

Go=5.5 T/m(x1o-2

1.0

6B/Bo(x1 o-4)
Bo=1.1T- - Calculation

05Measurement---,~~~~~~~-e~m=~~~~~~----x(mm)Fig. 3

Radial magnetic field distribution ofthe dipole magnet

B/BoL

CORE END CUT CASE 1'Fig. 5CORE END CUT CASE 2

Radial magnetic field distributionof the quadrupole magnets

Magnetic field measurement of the quadrupole magnets
Reducing the error of position measurement, theintegral magnetic field measurement apparatus with longtwin coil shown in Fig. 6 was d~4e~~ped and its
From themeasurement accuracy was 1 x 10 •measurement results of all magnets, it was confirmedthat the magnetic !~eld gradient uniformity ~GL/G 0 L wasin the required good field region
better than 2 x 10and satisfied the specification of the synchrotron.
The magnetic field gradient distribution along beamaxis was measured by the magnetic field measurement
apparatus with short twin coil. From thesemeasurement, it was known that the effective fringing
field gradient length_~as 53 mm and the deviation among
18 magnets was 2 x 10 •Bo=1.1T
Measurement--~--~~~--L-~--~-~---z(mm)100 200 300-300 -200 -100

Fig. 4Beam axial magnetic field di~tributionof the dipole magnet

Quadrupole magnet design
The design parameters required for the quadrupole
magnets are shown in Table 2. So as to satisfy
magnetic field gradient uniformity in the good fieldregi~n, the shape of cross section was determined bymagnetic field analysis used finite element method.
The shape of core ends was determinted by integral
magnetic field gradient measurement 3 ,bout two kinds of
The integral
core end model, as shown in Fig. 5.
gradient uniformity of case 2 was better than that ofcase 1, then the shape of case 2 was adopted.
Though the rated magnetic field gradient of thequadrupole focus magnets is different from that of thedefocus magnets, these fabrication is same; but these
exciting current is changed according to purpose.

-- 150--Fig. 6

Field measurement of the quadrupole
magnet by long twin coil

RF caiTity
RF caiTity design
The design parameters of the RF cavity are shown inTable 3. The cavity voltage of 60 kV is necessary toobtaine a reasonable quantum life time. The shape of
the RF caiTity is re-entrant type and the computer
program code SUPERFISH was g~ed to determine the innerFig. 7 shows electric
structure of the RF cavity.
line of TMOlO like mode in the RF cavity. Consideringa few opening are bored, the half of Q value andeffective shunt.impedance obtained by above program areshown in Table 3.
RF power system has cavity voltage feedback loop.
As detuning frequency at beam loading is small, thetuner is not movjd by feedback loop, but moved by
It is mainly used to compensate theremote contro1. 6
temperature increase effect.
OFHC copper was used in the body and the electrodesof the RF caiTity. The outer surface of the cavity
body, the electrodes, the tuner and the input coupler
are cooled by water.

The coupling coefficient between the RF cavity andthe input coupler, 6 = 0 to 6 was obtained by rotating
the input coupler. Now the input coupler is adjusted
to be ll=l.2.
Resonant frequency of the RF cavity was adjusted byvarying the gap length between the electrodes. The
measurement results in the vacuum at 40°C were resonant
frequency fr=ll8.0 MHz, effective shunt impedance
R h=l.28 MQ and Q=l5,200. It was known that them~asurement value of R h and Q was better than thesdesign value.

Table 3
Design parameters of the RF cavity
Resonant frequency
Q value
Effective shunt impedanceCavity voltageCoupling coefficient
RF power

118 MHz+0.25 MHz
9400
0.785 MHz
60 kV
1.2
10 kW
Fig. 8RF cavity-Analysis
Measurement

TMOlO like mode

LOcationFig. 9Fig. 7

Electrical field distribution of the RF cavity

References

Electric line of the RF cavity
1)
2)
3)

Measurement of the RF cavity
The low power test in the air was performed by thenetwork analyser. The RF cavity under the measurement
is shown in Fig. 8.
Fig. 9 shows the comparison of analysis andmeasurement about electric field of TMOlO like modealong beam axis. From this figure, it is clear thatthe analysis value is good agreement with the4)5)6)measurement value.

Maximum variation of resonant frequency obtained by
the tuner was 580 kHz and satisfied the specification.
Now the tuner is situated at 50 mm from the RF caiTity
surface.

-151-

A. Itano et. al., Proc. of the 5th Symp. on Ace.
Sci. & Tech. 1984, P.200.
T. Hori et. al.; INS-NUMA-24, 1980.
M. Kumada et. al., Proc. of the 2nd Symp. on Ace.
Sci, & Tech. 1978, P.75.
N. Kumagai, OHO '84 Seminar (in Japanese), 1984,P.lJI-27.
J.C. Slater, Microwave Electronics, D. van Nostrand
Co., 1950, p.232.
Y. Yamazaki, OHO' 84 Seminar (in Japanese), 1984,
P. IV-3.