DEVELOPMENT OF THE SUPERCONDUCTING BENDING MAGNETS FOR THE SR RING
T.Okazaki,Y.Hosoda,S.Isojima,T.Keishi,C.Suzawa,and T..Masuda
Osaka Research Laboratories, Sumitomo Electric Industr1es,Ltd.
1-1-3,Shimaya,Konohana-ku,Osaka,554 Japan
Abstract

Outline of the S.C. bending magnet

The superconducting bending magnets with a bending
radius of 0.5m and magnetic field of 4.0T have beendeveloped. The bending angle is 90 degrees therefore
four magnets are installed in the synchrotron radiation
ring. The main coils of the bending magnets are theiron-free curvature dipole coils and the conductors are
3-divided keystone type. The shim coils are epoxymolded quadrupole coils installed directly on the beamduct. The design of these coils was accomplished using
computer simulation. The designed electron beam energy
is 615 MeV and the radiation power from the beam to themagnet is 1kW so that the absorber cooled by liquid
nitrogen is set in the beam duct. Test results
validated the design.

This magnet is made of two groups of coils. One iscurved dipole coil, and the other is a curved quadrupole coil. Its cross section is described in Fig.1.
Among the coil types for application to the SR ring, adipole type coil(cosO winding) was chosen. The advantage of this type is that the magnetic field distribution is the most homogeneous, but it is difficult to
get many S.R. beamports. However, it is estimated that
two beamports can be taken from the coil end. Thisdipole and quadrupole,coil can be operated independently, so the magnetic field gradient (field index) of
this bending magnet can vary with the quadrupole coilcurrent. The magnetic field produced by the dipole coilis 4.0T when the main dipole coil cu~rent is 1774A andthe current density is about 270A/mm • The field index
can be varied from 0 to 0.5. The excitation rate is0. 34T/min.
No magnetic materials are used in this magnet to
avoid magnetic saturation problems. Since the magnetic
field distributions do not change with exciting current, their accuracy depend on onl~ the power source's
accuracy whose design value is 10- •The structure of dipole coil is a double pancake
coil, with an inner radius of 100mm and an outer radiusof 123.5mm. The conductor type used in the dipole coil
is a compacted strand cable. It is made of eight Nb-Ti
strands and insulated by two kinds of Kapton thin tape(see Fig.2). The keystone angle is the average size ofthe outer and inner layers. The keystone figure cable
is divided into three cables to reduce the current onethird. These 3 strands are wound in parallel and cured
in a hot press. After forming this coil, these threecables are joined at the magnet end serially. Thismethod has many advantages for making SR system compact. To make the same magnetic field, the volume ofthe power source, and current leads become smaller, andthe consumption of liquid helium can be reduced.

Introduction
Synchrotron Radiation (SR) for industrial applications is one of the key technologies for the next
generation; however, the usual SR ring system is toolarge to be applied for industrial use. Several companies are developing compact rings. Sumitomo ElectricIndustries,Ltd. (SEI), began development of a compact
SR ring system using four superconducting magnets(S.C.magnets). The S.C.magnet, with its strong magnetic field, presents a co~pact SR ring design, because
the strong magnet field can produce a small particle
bending radius. The electron beam energy is designed
615MeV with a stored beam current at 200mA and a peakwavelength of 5.\. The designed bending radius is 0. 5m.

dipole coil
inner layer

dipole coilouter layer

Kapton tape (25pm)
with overlap for
insulation

Kapton tape (SOpm)
with 1 Opm of epoxy

EE
LC:!

Fig 1. Cross section of the superconducting magnet.

Fig 2. Structure of the 3-divided compacted strandcable.

-175-The quadrupole coil set on the beam duct is moldedby epoxy resin, and the dipole coils are fixed between
the molded coils and the reinforcing collar which isfastened by bolts.
Its longitudinal length is about 2m. Since there
is not adequate space for a vacuum pump near the magnet, a cold bore type similar to the cryo pump wasadopted. The duct wall is cooled to liquid helium temperature. In order to avoid the increase of liquid
helium consumption by SR power, there is a SR absorberinside of the beam duct. The absorber itself is cooled; by liquid nitrogen, since it is also a kind of cryo
pump.

S=O~

2.S~

~

2.6<u~
~

<=C>

~

2.5B

2.54

-co

Design method of magnets

~-30

I
30

~

.&2u~

~

<=C>

~

changed by this field. Therefore a particle tracking
computer code was developed. This code solves the 3-D
motion equation by the Runge-Kutta method under a 3-D
magnetic fields, so that their longitudinal distribution along the electron beam path was considered. To
calculate the magnetic field of the magnet, we made asimulation model of dipole and quadrupole coils. Since
this magnet is iron-free type, finite-element-method
was not necessary. Therefore only the more important
coil model was modeled. This program can treat multipole effects; however, one defect of using the RungeKutta method on beam tracking is the long solution
time. Therefore, the dynamic aperture region cannot yet
be precisely calculated. It is estimated horizontally
about 70mm and vertically 15mm at the septum magnet.
The total ring design was done by the 2nd orderbeam tracking program. Results of the 2nd order simulation and 3-D real field tracking have good agreement
when the initial emittance is small. The setting
parameter of the current ratio between the dipole andquadrupole coil is calculated from the 3-D simulation
code.

...
.54

..

.5-60

Distance from the center (mm)Generally, for this iron-free type magnet, its
magnetic field leaks into a wide area and_includes
large amount of multipole components. These multipole
components disturb electron beam accumulation, therefore, the design of the magnet coil ends is very important. The magnet is designed considering the multipolecomponents reduction. At first, a large diameter ofdipole coil was selected, thus greater than acta-polecomponents could be ignored. Quad and sextuple components are still large. To compensate for these multipole components, two unique designs were considered.
One is to place the quadrupole coil in the dipole
coils. The main purpose of this design is adjustment of
the field index. The other is forming the sextupole
component of inverse polarity at the coil end. This
component compensated the original sextupole component
in coil main body and coil ends. Therefore at the coilends, the distribution of leakage magnetic field andsextupole component of it vary drastic. Fig.3 showsthese distributions at the median plane of this magnet.
S means the distance from the bending section of 90 degrees. By making sextupole component at the coil end,
the polarity of it changes between s=O and s=lOOmm.
Under these conditions, a good field uniformity of 5><
lo-4 more than 45mm at the coil center was obtained.
There are no precedents for SR ring construction
using such a small bending radius and a iron-free magnet. The beam tracking calculations were performed toconfirm the design results. For this kind of bending
magnet, the linear isomagnetic treatment of beam optics
and particle tracking is no longer adequate, because
the end magnetic field of this type magnet leaks into a.£iii"0"02.5

wide area, and the trajectory of the particles are

S=lOOmm.72.7

E-.04-.Ill-.Illu

~~~~

C>

-.04

~~

u

<=

60

"0"0~

30

S=300mm

S=200mm=-30

Distaoce from the center (mm)

-.12

<=
C>

~~

-.16-.16-.2-fiO-.12-30

3D60

Distance from the center. (mm)-.2--60-303D60

Distance from the center (mm)Fig 3. Distribution of the leakage magnetic field.

Magnetic field measurement
There are some difficulties when measuring themagnetic field of this magnet. One is the curvature ofthis magnet with a beam duct, and the other is the environment of the measuring point, such as at a liquid
helium temperature and in a high vacuum. Therefore NMR.sensor was used,however the NMR sensor can be used only
in a good field region. Six NMR sensors are placed in

the center of the magnet. In the coil ends, the magnetic field varies radically, so the NMR sensor can't
be used. Thirty Hall sensor were finally chosen tomeasure the distribution of the magnetic field along
the axis.
The magnet has been energized under a nominal current of 1322A. The results of the measurement dipole
fields by using NMR sensors at the magnet center are
displayed i~ Fig.4. In this figure, where solid lines
represent design values, measured and design data arein close agreement. The variation of the dipole fieldalong the electron path is shown in Fig.5. Again close
agreement between measured and design values were obtained. In this experiment, by the thermal disturbancethrough the sensor holders, the magnetic field didn't
reach the design value; however, in another series ofexperiments without sensor holders, it exceeded thedesigned field. Training results of this. magnet isshown in fig.6. Current margin was taken about twotimes. When energized the quadrupole coil inside thedipole coil, reduction of achieved current wasn't observed.
·-176-

2. 991r---... ----,---,-- ..,--r--.--- ,!m=':322A
Iq=10.5A
45 deg000003E..j-J

00000

c:00Q)c....
c....
:::::1uCD0calculation

o2.9..?soexperiment-20-40

020

260

40

46B

101214

Number of Quenches

Distance from Center (mm)Fig 6. Training results.

Fig 4. Magnetic field distribution at the magnet center
measured by NMR sensors.

3Conclusions
A new type of iron-free bending magnet for a615MeV SR ring with bending radius of 0.5m and magnetic
field of 4.0T has been developed, and the measured data
validated design,
One of these magnets was set in the SR ring in
September 1989, and SR ring could accumulate severalcurrents. Now other magnets are ready to be set in theSR ring.

Im=1202A
lQ=10.5A

8 portHall No.23

20experimentcalcu!ation

Acknowledgments
The authors wish to thank Dr.Tomimasu of theElectrotechni cal Laboratory for his useful advise.
This project is entrusted by the Research Development Corporation of JAPAN.

0References
-1

0200

400600

BOO

1000

1200

Longitudinal length (mm)Fig 5. Magnetic field distribution along the electron
path measured by Hall sensors.

1. Takada, H., Tsutsui, Y., Tomimasu, T. and Sugiyama,
S., High beam current storage at low energy for compact synchrotron radiation rings, Rev. Sci. Instrum.,
1989, 1630-1634
2. Tomimasu, T., Noguchi, T., Sugiyama, S., Yamazaki,T., and Mikado. T., An electron undulating ring for
VLSI lithography, IEEE Trans. Nucl. Sci .. NS-32, 1985,
3403-177-