PROGRESS

IN MAGNET SYSTEM FOR THE

SPrinq-8

STORAGERING

J.Ohnishi, Y.Oikawa, and S.Motonaga
RIKEN-JAERI Synchrotron Radiation Facility Design Team
2-28-8 Honkomagome, Bunkyo-ku, Tokyo 113 Japan
Abstract
The first-step design of a dipole, quadrupole, andsextupole magnet for the SPring-S storage ring has been
finished, and the more detailed design is in progress.
At the same time, the prototypes of these magnets areunder construction. This paper describes the mechanicaldesign, and field quality calculated by means of 2dimensional numerical program.
Introduction
The storage ring of SPring-S is being designed by
RIKEN to be a highly-brilliant synchrotron-radiation
source.l It was designed in Chasman-Green lattice to
get an emittance lower than lo-B mrad. The ring is 1437
m around, containing 48 unit cells. The layout of acell is shown in Fig.l. Four cells locatedsymmetrically have no bending magnet, because longstraight sections are considered for special insertion
devices. Those sections can be made by a rearrangementof the magnets in future.
Magnet system contains 88 dipole, 480 quadrupoles,and 336 sextupoles. There are also 576 dipolecorrectors; 364 of them are incorporated with thedipoles or sextupoles by the addition of extra
windings, 96 of them individual horizontal correctors,
28&2.7 -ir----mu

and 96 of them for both vertical and horizontal
corrections. Furthermore, three septum magnets and four
kickers are accommodated for beam injection.2 All themagnets except for several pulse magnets are operated
statically (de operation), because the beam is injected
after accelerated up to the nominal energy (8 GeV) inthe booster synchrotron.3
The required field qualities for the dipole,quadrupole, and sextupole magnets are very stringent asshown in Table 1 since this storage ring is supposed tohave extremely low emittance beam. Therefore, we havedesigned the pole geometry of magnet carefully bycarrying out numerical calculations of magnetic field$with two-dimensional programs, LINDA4 and TRIMSEach magnet itself is assembled from a stacked
core which is a 0.5 mm thick silicon-steel plate andstainless steel end plates of 25 mm (20 mm) thick. The
choice of laminated structure was made in the aspectsof the identity in magnetic field quality, andconstruction cost.
At present, full-scale prototypes of dipoles,
quadrupoles, and sextupoles are being built in order toverify the designs by measuring the magnetic fields.
They will be also used to improve the construction
techniques. Moreover, a design of power supply system6·
for the magnets is under way, together with thedevelopment of high accuracy field-measurement systems.

J '" ·'

8240.0

B '
Q '

S '

TD BE,.,.

C ,('/)M

CH/V)

M 'CR•

B BE4M

BENDING ~AGNE:T
OUAD~UPLE MAGNETSEXTUPOL[ MIIGNE'T
CO~RECT!ON DIPOLE
BEA"' MONITORCROTCHE BEA~

03 S2 02 S! O!
(CHl(CVl!D!0Fig.l ~ ~~~a~f~~=~; ~[ngipole, quadrupole, sextupole, and correction magnets in a cell
70

Table 1.
Required field quality of dipole, quadrupole, andsextupole magnets
Ma~etDiEole

QuadruJ2!2leSextuEole

Maximum fieldstrength
Gap distanceor bore radius
Effective field
lengthField uniformity

0.655 T

18 T/m360 T/m2

65 mm

45 mm

55 mm

2.863 m0.5, 0. 6,l.lm
AGl/Gl
<5 X 10-4x=±35 mm:x:=±15 llllll

0. 6, 0.45 m

5210Region size

ABl/Bl<s x lo-4x=±40 mm:x:=±l7 llllllNU')<D

radial shims-'

AGl/Gl<1 x lo-3x=±35 mm:t=±lS mm

Dipole magnet
The cross-sectional view of a dipole magnet are
shown in Fig.2. A C-shaped rectangular configuration
has been chosen because of the following reasons; it iseasy and economic to construct and also easy toaccommodate beam chambers and to measure the field.
The height of gap was determined as 65 mm, which
provides 40 mm for beam clear space in a vacuum
chamber, and 7 mm x 2 for the chamber wall thickness, 2mm x 2 for the thermal insulation, and finally 3 mm fora clearance at radial shims (2 mm x 2) . The pole width
was 240 mm to insure the high-quality horizontal fieldregion of 106 mm including a sagitta of 26 mm.
The geometrical accuracy of the finished core isdeduced to be within ±0.02 mm for the gap height, and±1 mm for the magnet length from the measurement on theprototype.

Fig.2 The cross-sectional view of a dipole magnet
The calculated field distribution of a dipole
magnet is shown in Fig.3. The maximum deformation of
the poles due to the magnetic force, which appears as a
reduction of the gap, was estimated to be about 10 ~by a simple FEM. This value is as small as thegeometrical core accuracy, and the corresponding change
in the field distribution is also small enough as shownin Fig.3.
The coils of dipole are composed of main andauxiliary ones. The main coils are constructed to be
two pancakes of 14 mm x 23 mm copper conductor with acooling channel of 10 mm diameter. On the other hand,the auxiliary coils are capable of providing a-163-Table 2
Main magnets parameters
DiE2leNumber of magnets
Maximum strength
Effective length
Gap or Bore radius
Magnetomotive force
Turns per pole
Conductor size
Current
Current density
VoltagePower
Cooling water circuits
Water flow
Pressure drop
Tem22rature rise

88
0.655 T
2.86
65
3.5xlo414
l4x23-hO
1250
5.1
20.3
25.3
2
18.1
5.0
20(m)
(mm)
(AT)
(mm)
(A)
(A/mm2)(V)(KW)(1/min)(bar)!oCl

SextuEole

guadruEole
192
0.5

10.8
10.2
47.32.0

192
96
18 T/m
0.6l.l45
1. 5xlo4
16ll.5x16-cp5
940
5.8
23.8
13.0
12.2
22.4
488.7
16.0
3.2
2.6
20288
48
300 T/m2 360 T/m2
0.45
0.655
7.0xlo3 8.3xlo3
228x8-c)l3, 5, c)l4, 0
320
380
7.0
5.9
27.2
18.3
10.3
5.9
66
7.4
4.2
4.1
2.3
20

magnetomotive force of 600 [AT) at air cooling. They
will be employed to compensate for a random error inmagnetic strength (Bxl) from one magnet to another, andalso for COD correction.
The major parameters of dipole magnets are given
in Table 2.

-1.00101.0008w 1.0006

Ia> 1.0004~ 1.Cl002"-·' q ,iil 1.0000

Non-defonned
Defonned

A~~AB
cD~ 0.9998

m

0.9996

X(mm)
31.82
52.50
64.17
70.00

Y(mm)
31.82
19.29
15.00
15.00

0.99940.99920.9990·1 0-8-6-4-202

4

6108

X (em)

Fig.3 Calculated transversal field distributions of a.dipole magnet normalized at x=O (B=0.655 T).
Deformation due to the magnetic force isconsidered for one case.
Quadrupole magnet
The cross-sectional view and pole profile of aquadrupole magnet are shown in Fig. 4 . All thequadrupole magnets in the storage ring are same intheir cores except the lengths. There exist threedifferent lengths; 0.5 m, 0.6 m, 1.1 m. The bore
diameter (90 mm) was decided based on the size of beamchamber, and the uniform field region. The upper andlower halves of the magnet are separated magnetically.
They are joined through stainless steel parts, because
the structure of joint parts is supposed to bedifferent depending on the location to provide space
1.005
1.004 ~-----w-1.003 ~---->1.002 ~----i= 1.001 1--<..J 1.000w~ 0.9990.998

in 0.997

15T/m
16T/m
18T/m
20T/m

._---\.,~l\\\10.996

•02.

3

4

for a photon beam line. The magnetic core geometry of
all the quadrupoles can be, thus, kept identical. On
the other hand, the mechanical design of joints has notbeen completed yet.
The calculated distributions of field gradient(B') are shown in Fig.5 along a radial direction. An
adjustment by~ shape of radial shims was. also included.
so that the B' strengths are intensified along theradial direction as indicated in Fig.5. The reason isthat an .integrated gradient over the magnet is presumed
to be decreased along the direction. The integrated
gradient distribution can be corrected simply by adding
end shims if necessary.
It is desirable that all the quadrupoles areoperated within gradient strengths of 16 and 18 T/m forthe normal operation and the maximum, respectively,
because they are satisfied with the severe required
field quality (see Table 1). But we believe that apossibility of the maximum strength should be verified
by measuring the real field of the prototype for thesake of shorter magnet length .
The major parameters are listed in Table 2.
Sextupole magnet

I

0.995

Fig.4 The cross section and pole profile of aquadrupole magnet

5X (em)Fig.5 Calculated distributions of the field gradient(B') of a quadrupole magnet for the severalstren<}thsSeven sextupole magnets are placed in a unit cell;
three o'f them correct chromaticities and the remaining
four extend the beam dynamic aperture. Furthermore, itis planned that most of sextupoles in the ring provide
even a horizontal or vertical dipole field to steer thebeam by adding special coils to them. An arrangement ofthe sextupoles in a cell and their field strength in apominal mode are shown in Table 4.

-164-

Table 4
Parameters of Steering Windings

TABLE 3.
Family of sextupole magnets

Sl!Sl! S2 !S2)
-239
210
0.45
0.45
Hv

B" (T/m2)
Leu (m)Steering

SD!S3! SF!S4!
-259
347
0.45
0.60
HNone

SD!S5!
-259
0.45
H

S3!S6!
-178
0.45v

S4!S7!
286
0.45
H

H: Horizontal steering coils are incorporated
V: Vertical steering coils are incorporated
900

X(mm) Y(mm)A- 0.00 55.00
B 10.96 57.18·c 16.71 58.94
D 19.13 61.13
E 22.88 67.62
F 45.00 135.68
Fig.6 The cross section and pole profile of a sextupole
magnetTwo different types have been designed in yoke
structure: One is completely symmetric and the otherasymmetric. Fig.6 shows a cross-sectional view of thesextupole magnet, which has the asymmetrical yoke
structure. This is due to an extra room for theextraction of a photon beam. The bore diameter is 110
rom. The contour for all the pole tips is the same,ro3.:r3cos39 with radial shims, as shown in Fig.6. The
widths of a pole and a yoke are designed to be thickenough so that the maximum strength of sextupole field
can be excited up to 360 T/m2 without any correction
field, or 300 T/m2 with a correction dipole field of
0.06 T. The major parameters of sextupole magnet arealso listed in Table 2.
Fig.7 shows the calculated field distributions ofa sextupole magnet with asymmetrical yokes. The Y-axis
indicates dBy/dx/x on a medium plane. Asymmetricalfield distributions are caused by the core geometry,and originated from a quadrupole component. Its value
was, however, estimated to be only 1.3 x lo-3 T/m,which is smaller than the gradient errors of aquadrupole magnet, suggesting no serious influence to abeam.
All the sextupole magnets except for 'SF' family
have auxiliary coils for providing steering dipole
fields. The coils are indicated by 'H' for horizontalw>

i=<...Iwa:~~
m

1.005
1.004
1.003
1.002
1.001
1.000
0.999
0.998
0.997
0.996
0.995

--'\.
'\.

...

-6~

II
1=6cm
1=8an

-2

0

2

Sl,S3,S5,S7192(m)0.45(rnrad) 1.0(T)
0.059
24340
136(mm2)
2.4 X 4(A)
12.4
12.4
{A!mu2) 1.3
1.3
{V)
12.6
5.1(W)
105
63

S2,S696
0.45
1.0
0.059
4275
2.4 X 4
9.5
1.0
7.3
70

steering and 'V' for vertical in Fig.6. In the actual
magnets, either 'H' coils or ··v• coils are installed asin Table 3. Table 4 shows the parameters of steering
windings. The maximum field strength is 0.06 T, which
gives an 1 rnrad kick to the beam, and is confirmed tobe sufficient through a simulation of the COD
correction.
Fig. 8 shows the calculated distributions of ahorizontal and a vertical dipole field induced by thesteering elements in a sextupole magnet. Bx(y) on a x=O
plane is plotted for the horizontal fields, and By(x)on a y=O plane for the vertical. Though the dipole
field is superimposed on the sextupole field in aactual magnet, the change in field distributions washardly seen according to the 2-dimensional
calculation. 7
1.10
1.08
1.06
> 1.04i= 1.02
1.00~ 0.98w:5--III_/

horiz. steer
vert. steer.............,/__.... _/Jf

~

~0.96

'm 0.94
0.92
0.90
0.0

0.5

1.0

1.5

2.0

2.5

~

3.0

3.5

4.0

X, Y (em)Fig.8 Calculated distributions of steering dipole
fields provided by correction elements
incorporated with a sextupole magnet.
Normalized at x=O (0.06 T).
Conclusion
We have completed the preliminary design of adipole, quadrupole, and sextupole magnet. At present,prototypes of these magnets are being built. We areplanned to measure the characteristics of theprototypes and improve the design.

1. M.Hara, et al.,Proc. of Particle Accelerator Conf.,
Chicago, U.S.A., 1989 .
2. H.Miyade,et al., presented at this symposium
3. H.Yokomizo, et al.,Proc. of Particle Accelerator
Conf., Chicago, U.S.A., 1989.
4. K.Endo, et al., KEK Accelerator-!, 1972.
5. K.Endo, et al., KEK Accelerator-2, 1974.
6. H.Takebe, presented at this symposium
7. J.Ohnishi, Proc. of 11th Int. Conf. on Magnet
Technology, Tsukuba, Japan, August, 1989.

I-4

Family ,Number of magnets
Physical length
Kick angle
Peak field
Number of coils
Turns per pole
Conductor size
Current, max.
Current density
Voltage per coilPower per coilvert.
Coil cReferences

A#'t?

Ahoriz.
Coil A Coil B

46X(cm)Fig.7 Calculated distributions of the field gradient(B") of a sextupole magnet with asymmetricalyokes. 't' indicates the thickness of an extendedyoke.

-165-